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Review

Protein-Based Strategies for Non-Alkali Metal-Ion Batteries

by
Qian Wang
1,
Chenxu Wang
2,* and
Wei-Hong Zhong
2,*
1
Department of Mechanical Engineering, The University of Texas at Dallas, Richardson, TX 75080, USA
2
School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, USA
*
Authors to whom correspondence should be addressed.
Batteries 2025, 11(9), 318; https://doi.org/10.3390/batteries11090318
Submission received: 18 July 2025 / Revised: 13 August 2025 / Accepted: 19 August 2025 / Published: 26 August 2025
(This article belongs to the Special Issue Sustainable Materials and Recycling Processes for Battery Production)
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Abstract

Batteries are a cornerstone of modern technology that supports a wide range of applications including portable electronics, electric vehicles and large-scale energy storage for renewable power systems. Despite their widespread use, commercial Li-ion batteries are limited by the mineral resources of Li. The rapidly growing battery market demands alternative battery systems, such as non-alkali metal-ion batteries, that are capable of delivering comparative energy densities. In the meantime, improving the performance of the batteries via generating sustainable strategies has been broadly studied. Proteins, as re naturally evolved macromolecules that possess diverse structures and functional groups, have been demonstrated to be able to transport various metallic ions inside bio-organisms. Therefore, active studies have been carried out on the use of natural proteins (e.g., zein, soy, fibroin, bovine serum albumin, etc.) to enhance the electrochemical performance of non-alkali metal-ion batteries. This review provides a comprehensive summary of recent advances on the studies of protein-based strategies for non-alkali metal-ion batteries and outlines perspectives for future sustainable electrochemical energy storage systems.

1. Introduction

Global energy demand has increased significantly due to rapid industrial growth and electric device development in the past 30 years. Renewable energy sources, such as solar, wind and hydropower, have become key global strategies to address the environmental impacts and resource limitations of fossil fuels [1]. The widespread implementation of renewable energy has significantly reduced greenhouse gas emissions generated from conventional thermal power plants. However, the intermittent and seasonal supply of solar and wind energy leads to fluctuating power output, bringing a critical challenge of grid stability and reliability. To address this issue, various energy storage systems have been applied to temporarily store the electric energy produced by renewable energy plants [2]. Among the energy storage systems, rechargeable batteries offer a practical and scalable solution for storing excess energy during periods of surplus generation and effectively delivering it during peak demand. Currently, the widely used batteries are Li-ion batteries, which dominate the market of consumer electronics and electric vehicles due to their high energy density and long cycle life [3]. However, the limitation of Li mineral resources restricts their future sustainable application in large-scale and stationary energy storage systems.
In recent years, significant research has been directed towards the development of alternative battery systems that rely on non-alkali metal-ion batteries, such as Zn-ion batteries [4], Zn–air batteries [5], redox flow batteries [6], bio batteries [7], and so on, have emerged as promising candidates for next-generation grid-scale energy storage. These batteries possess the combined advantages of affordability, environmental safety, aqueous electrolyte compatibility, and the potential for a long lifecycle [8]. Despite these advantages, challenges such as limited power output, low energy density or capacity degradation still hinder their practical deployment [9]. Different approaches based on various materials, such as heteroatom-doped carbons [10,11], transition metal oxides/sulfides [12,13,14,15,16], conductive polymers [17,18], metal–organic frameworks [19,20], and so on, have been reported to improve conductivity, redox kinetics, and active site density. However, the non-alkali metal-ion batteries still face challenges such as poor cycling life, low capacity, and limited environmental sustainability. To address these challenges, the use of specific natural biomaterials have garnered increasing attention based on their natural characteristics [21,22,23].
Proteins are complex polymeric macromolecules composed of many amino acids. Each amino acid consists of an amino group, a carboxyl group and a side chain. The side chain varies among different amino acids and determines their specific chemical properties [24]. Based on the characteristics of these side chains, amino acids can be classified into nonpolar, polar, aromatic, positively charged and negatively charged types. Nonpolar amino acids such as glycine (Gly), alanine (Ala), and leucine (Leu) possess aliphatic hydrocarbon side chains that promote van der Waals interactions [25]. Aromatic amino acids including phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) contain bulky ring structures that contribute to reduced molecular flexibility. Polar and uncharged residues, such as serine (Ser), threonine (Thr), and cysteine (Cys), are capable of forming hydrogen bonds, enhancing structural stability. Meanwhile, positively charged amino acids (e.g., lysine (Lys), arginine (Arg) and histidine (His)) and negatively charged ones (e.g., aspartic acid (Asp) and glutamic acid (Glu)) facilitate strong electrostatic interactions or ionic bonding. These diverse side chains allow proteins to participate in a variety of molecular interactions, including ionic bonds, hydrogen bonds, and disulfide linkages, which collectively govern their physical and chemical behavior. As a result, proteins display a wide range of properties (e.g., molecular weight, isoelectric point, shape, size, and mechanical strength) that are critical for their biological and functional roles.
Natural proteins often adopt highly entangled structures due to numerous intramolecular interactions that stabilize their native conformation. To effectively harness their functional groups, denaturation processes were applied to disrupt these complex structures without altering the amino acid sequence. Denaturation unfolds proteins from their quaternary or tertiary structures to simpler secondary or primary structures. This structural unfolding enhances the accessibility of reactive groups and can be achieved through various methods, including thermal treatment and exposure to chemical agents. Different denaturation strategies target specific molecular interactions. For example, heat disrupts hydrogen bonds and hydrophobic interactions, which are as observed in processes like egg boiling. Alcohols interfere primarily with hydrogen bonding, explaining their use in disinfection. Acids and bases break salt bridges by altering the ionization state of charged side chains. Salts and reducing agents can cleave disulfide bonds, leading to further protein unfolding. The extent and method of denaturation significantly influence the resulting physicochemical properties of proteins, such as solubility, surface charge, and reactivity [26]. These modified properties are particularly advantageous for electrochemical energy storage applications such as batteries, where tailored surface interactions and functional group accessibility are critical. For example, soy protein [27,28,29,30,31,32], zein [21,22,23,33,34,35,36,37], bovine serum albumin protein [38,39], silk protein [40] and eggshell protein [41,42] have been applied to synthesize battery components including active materials, separators, electrolytes, binder and protective films for Li-based batteries, which have been well summarized in previous reviews [43,44,45]. However, the reported applications of protein in non-alkali metal-ion batteries have not been systematically summarized.
In this review, we summarize recent advances in the application of protein-based and protein-derived materials in non-alkali metal-ion batteries for improving their electrochemical performance and environmentally benign behavior (Figure 1). Specifically, we categorize the applications of protein materials into several sections based on different battery components and battery systems. In the second section, we summarized the reported applications of protein-derived biomass carbon and protein-modified active materials in non-alkali metal-ion batteries including Zn–air batteries and vanadium redox flow batteries. In the third and fourth sections, protein-derived film for stabilizing Zn metal anodes and protein-based hydrogels and gel polymer electrolytes for high-performance Zn-ion batteries were introduced. Protein-based and protein-derived catalysts in bioelectrochemical systems (e.g., biochemical microbial fuel cells and biochemical H2-NH3 systems) and polypeptide organic radical active materials were summarized in the fifth and sixth sections. In the last section, the conclusion and perspectives of protein applications in non-alkali metal-ion batteries were summarized.

2. Protein-Derived Materials for Electrodes

2.1. Protein-Derived Carbon

Biomass carbon has emerged as a popular material as the anode in batteries owing to its multifunctionality resulting from its diverse morphology and chemical composition. Specifically, biomass carbon with a mesoporous structure offers several advantages, including a large specific surface area that facilitates high electrical conductivity, ionic transfer channels and good wetting with the electrolyte [11,46]. Consequently, biomass carbons with high specific surface area hold great promise as electrode materials for low-cost non-alkali metal-ion batteries. Through changing the parameters of different activation processes and using different raw biomaterials, biomass carbon can be tailored to exhibit tunable pore sizes and chemical constituents, making it suitable for use as conductive matrices for electrodes in non-alkali metal-ion batteries such as Zn–air batteries and vanadium redox flow batteries (Table 1).

2.1.1. Protein-Derived Carbon for Electrodes of Zn–Air Batteries

Silk protein (extracted from Bombyx mori silkworm cocoons) has been utilized as a precursor to synthesize porous nitrogen-doped nanocarbon (SilkNC/KB) featuring abundant structural defects, which was subsequently employed as electrocatalysts for the oxygen reduction (ORR) and oxygen evolution reactions (OER) in Zn–air batteries [47]. The synthesis processes were impregnating Ketjenblack (KB) into a silk fiber solution followed by drying and calcination, resulting in a randomly interconnected nanoparticle structure (Figure 2a). High-resolution transmission electron microscopy (HRTEM, JEOL JEM2010F) revealed a hybrid composition of porous, distorted graphitic, and amorphous regions within the nanocarbon (Figure 2b). The X-ray photoelectron spectroscopy (XPS, Thermo Scientific Escalab 250Xi) analysis of the N 1s spectrum identified pyridinic and graphitic nitrogen as the dominant species, which are known to contribute significantly to ORR/OER activity (Figure 2c). Figure 2d presents the ORR performance of nanocarbon samples synthesized with varying Ketjenblack-to-silk ratios. The SilkNC/KB with an optimal ratio of silk and KB had a half-wave potential (E1/2) of 30 mV and a current density of approximately 6 mA cm−2, indicating excellent conductivity and a high density of catalytic sites. Consequently, Zn–air batteries incorporating the SilkNC/KB electrode exhibited strong cycling stability, exhibiting a voltage gap of 1.03 V and a voltaic efficiency of 51.4% after 100 cycles (Figure 2e).
In a separate study, protein-rich root nodules were transformed into effective electrocatalysts for Zn–air batteries [48]. The root nodules contain two metalloproteins, olybdenum-iron (MoFe) protein and iron (Fe) protein, which function as enzymes within the nitrogenase complex. The root nodules were carbonized and activated by ZnCl2 (TCI, 98%) within a temperature range of 700–1000 °C. This thermal treatment enabled the in situ formation of a carbon-based catalyst doped with sulfur, nitrogen, molybdenum and iron, while simultaneously achieving a high specific surface area (SSA) and high degree of graphitization (Figure 2f). The inherent metal atoms embedded in the protein polypeptide chains promoted the uniform distribution of metal clusters within the resulting porous carbon matrix, thereby significantly improving its electrocatalytic performance (Figure 2g).

2.1.2. Protein-Derived Carbon for Electrodes of Vanadium Redox Flow Batteries

In vanadium redox flow batteries, electrochemical reactions primarily occur at the interface of electrode materials such as carbon, transition metals and noble metals [53]. These electrochemical reactions are key to converting stored chemical energy into usable electrical power. The VO2+/VO2+ couple at the positive electrode is generally the rate-limiting step due to its slower proton-coupled electron transfer process. Enhancing the efficiency of vanadium redox flow batteries requires electrodes with a three-dimensional architecture that not only facilitates efficient electrolyte circulation but also offers a high specific surface area to expand the active reaction sites. These structural features help reduce redox reaction overpotentials and boost the electrical conductivity of electrodes in batteries.
Silk protein-derived carbon fabrics (SCFs) obtained through carbonization at temperatures between 800 and 1200 °C have been explored as electrode materials for vanadium redox flow batteries (Figure 3a,b) [49]. These SCFs provided abundant nitrogen and oxygen heteroatoms that originated from the polypeptide backbone of protein, contributing to low peak potentials (ΔEp) of approximately 164.5 mV and 164.6 mV for the catholyte and anolyte, respectively, at a scan rate of 5 mV s−1. In a separate study, a twin cocoon protein (Figure 3c, obtained from a farm in southern China) underwent hydrothermal treatment (Figure 3d) followed by carbonization (600–1000 °C) to yield a nitrogen- and oxygen-doped, self-supporting carbon monolith (Figure 3e). The protein-derived carbon monolith possessed abundant active sites with nitrogen defects, promoting the electrochemical activity of both V2+/V3+ and VO2+/VO2+ couples. Therefore, the carbon improved the long-term stability of vanadium redox flow batteries [50,51]. Additionally, the carbon derived from a corn protein (zein, Sigma-Aldrich, St. Louis, MO, USA) has been employed as a catalytic electrode material (Figure 3f,g) [52]. The zein-derived carbon possessed a high specific surface area enriched with oxygen-containing groups and active sites for vanadium redox reactions, facilitating enhanced electron transport and ion kinetics (Figure 3h). The superior performance of protein-derived carbon materials can be attributed to two main characteristics. One characteristic is the integrated, porous networks that offer improved conductivity, structural flexibility and permeability; the other is the defect-rich surfaces with high nitrogen and oxygen content that promote redox activity and reversibility.

2.2. Protein-Modified Active Materials

Pig blood (obtained from the local butcher shop) is a protein-rich biological material abundant in hemoglobin, which has been employed to synthesize an electrocatalyst featuring atomically dispersed Fe sites embedded within a two-dimensional, porous carbon matrix (Figure 4a–c) [54]. Zn salt (Zn(NO3)2·6H2O, Sigma Aldrich, St. Louis, MO, USA) was introduced in controlled amounts into the precursor mixture solution as an activation agent. Through strong coordination with the proteins, Zn ions formed uniformly distributed hydrolysates in the solution. After a hydrothermal treatment and pyrolysis process at 900–1000 °C within a different atmosphere, a porous architecture with well-dispersed Fe-N-C active sites was obtained (Figure 4d). The resulting Zn-assisted Fe single-atom catalyst calcinated at 950 °C within an NH3 atmosphere (Zn/FeSA-PC/950/NH3) contained most abundant Fe-N sites compared to other samples (Figure 4e). Zn/FeSA-PC/950/NH3 exhibited a high ORR performance that was characterized by a superior limiting current density along with a more positive onset potential among the samples (Figure 4f). Consequently, the Zn/FeSA-PC/950/NH3 catalyst delivered a peak power density of 220 mW cm−2 in Zn–air batteries (ZABs) (Figure 4g).
In an earlier work, the Fe-N-C framework composites were synthesized using soybeans as the carbon and nitrogen source. Soybean was mixed with FeCl3·6H2O via grinding and followed by a pyrolysis process to obtain the composites (Figure 4h) [55]. These composites served as a scaffold for the vertical growth of ultrathin NiFe-layered double hydroxide (NiFe-LDH) nanosheets (Figure 4i) that were achieved through a simple coprecipitation process (Figure 4j,k). The nanosheets preferentially nucleated at the defect sites and oxygen-rich regions of the Fe-N-C substrate (Figure 4l), resulting in a composite with exceptional oxygen evolution (Ej=10 = 1.53 V vs. RHE) and oxygen reduction (E1/2 = 0.91 V vs. RHE) reaction activity (Table 2). Moreover, the catalyst demonstrated impressive durability and operational stability in ZABs (Figure 4m).
In another study, bovine serum albumin (BSA), a protein in animal blood, bovine serum albumin (BSA) served as both the exfoliating and dispersing agent, enabling the rapid production of stable hybrid suspensions in large quantities [56]. Meanwhile, a simple and one-pot top–down approach has been used to efficiently synthesize MoS2/graphene (MoS2/Gr) hybrid nanoplatelets in aqueous solution. In this process, the phenyl and disulfide functional groups of BSA strongly interacted with MoS2, exhibiting a binding energy of 0.51 eV that was significantly higher than the interlayer binding energy of MoS2 (0.21 eV), which facilitated effective exfoliation. When applied in Zn–air batteries, the MoS2/Gr hybrid with a 1:13 molar ratio exhibited enhanced ORR performance, delivering a high open-circuit voltage of 1.4 V and a notable specific energy density of around 130 Wh kg−1.

3. Protective Films for Zn Metal Anodes

Zn-based batteries have gained significant attention due to their high theoretical capacity (820 mAh g−1), low cost, environmental safety and compatibility with aqueous electrolytes. However, their practical deployment is hindered by the uncontrollable Zn dendrite formation on Zn metal anodes during repeated plating/stripping cycles. The Zn dendrites pierce separators and lead to internal short circuits. Meanwhile, broken Zn dendrites form isolated Zn metal particles on Zn metal anode during cycling. The isolated Zn metal particles increase interfacial resistance and the exposed broken solid electrolyte interfaces lead to electrolyte depletion and eventual cell failure. Therefore, effective strategies to regulate Zn deposition and suppress dendrite growth are essential for prolonging the lifespan and improving the safety performance of Zn-based batteries.
In aqueous Zn-based batteries, Zn2+ are surrounded by a solvation shell that is composed of water molecules or coordinated functional groups from electrolyte additives. The configuration and stability of the solvation structure play a critical role in governing ion migration and deposition behavior. During stripping/plating processes, Zn2+ first shed part of their solvation shell before nucleating on the anode surface. A uniform and stable solvation promotes even Zn2+ flux distribution across the electrode, which can enable homogeneous nucleation and smooth metal growth. However, the general conditions are unstable or anisotropic solvation, which leads to localized current density spikes, causing uneven deposition and dendrite formation. Protein-based additives, owing to their multiple coordination sites and amphoteric nature, have been reported to tailor the Zn2+ solvation environment by replacing water molecules in the solvation shell, directing ion deposition into dense and dendrite-free morphologies.
A biomolecule-assisted approach using collagen hydrolysate (CH)-modified separator has been reported to suppress dendrite formation in Zn metal batteries [57]. The CH-coated separator, collagen hydrolysate on absorbed glass mat (CH@AGM), was prepared by dissolving CH in hot water and then uniformly coating it onto a porous AGM substrate (Figure 5a). The symmetrical Zn|AGM|Zn cell delivered a current of −46 mA at −0.2 V and maintained at −43 mA. Comparatively, the Zn|AGM + CH@AGM|Zn configuration shows a steadily increasing current beginning at −0.34 V (Figure 5b). This CH coating introduced a negatively charged surface in both aqueous electrolytes, facilitating enhanced surface conduction and ion transport regulation (Figure 5c). The CH molecules interacted strongly with Zn2+ due to the presence of amino acid sequences (mainly glycine, proline and hydroxyproline) capable of forming stable complexes. Moreover, anions such as SO42− or PF6− were driven away by the intense electric field, which amplified ion depletion in the bulk and triggered a “deionization shock” phenomenon (Figure 5f). This process promoted uniform “shock electrodeposition” behind the shock front and effectively suppressed the formation of dendrites. In the aqueous electrolyte containing 2% CH, the Zn coating on the anode surface appeared only partially distributed, featuring fine grains smaller than 1 μm (Figure 5d). In contrast, the pristine aqueous electrolyte produced a more continuous granular structure, with grain sizes reaching up to 10 μm on the anode surface (Figure 5e). The symmetrical Zn|AGM + CH@AGM|Zn cell demonstrated lower mass transfer-controlled potential values and improved potential retention compared to the symmetrical Zn|AGM|Zn cell (Figure 5g). Moreover, Zn||LMO full cells with CH@AGM exhibited over 600 stable cycles at 1 C and maintaining >90% capacity retention with high-loading cathodes of 24 mAh cm−2 (Figure 5h). Even under high-temperature conditions (60 °C), CH@AGM-stabilized batteries showed minimal performance degradation. The strategy was validated in large-volume batteries (5 Ah, 65 Ah, and 200 Ah Zn metal cells) that demonstrated the scalability.
Zn metal anodes are suffering from the parasitic reactions at the Zn/electrolyte interface due to the strong activity of water molecules. In a recent study, to suppress the reactions between water and Zn, silk fibroin was reported as an additive for various aqueous electrolytes with different salts (ZnSO4, Zn(CF3SO3)2 or ZnCl2) [58,59,60,61]. The fibroin protein molecules have a secondary structural transformation from regular α-helices to random coils in the electrolytes, forming a [Zn(H2O)4(fibroin)]2+ solvation structure and weakening the hydrogen bond of water. Meanwhile, the fibroin additive generated a self-healing protective film on the Zn anode, regulating Zn ion deposition and alleviating dendrite growth. As shown in Figure 5i, Zn anodes cycled in pure ZnSO4 electrolytes exhibited a rough surface morphology characterized by irregular clusters of vertically aligned 2D hexagonal flakes. In contrast, the addition of 0.5 wt% SF resulted in a smoother and dendrite-free surface (Figure 5k). Furthermore, prolonged cycling in ZnSO4 alone led to increased dendrite accumulation on the separator. As a result, the symmetrical Zn|Zn cell displayed an excellent cycling lifespan of >500 h. The Zn|KVO full cell had a good cycling stability (capacity retention is 82.7% at 200th cycles at a current density of 0.2 A g−1 (Figure 5j). In another work, the eggshell membrane was applied as a protective film for Zn metal anode [62,63]. The eggshell membrane is mainly composed of fibrous proteins, particularly collagen, initiating Zn nucleation and inducing an even ion flux, thereby forming a uniform deposition of Zn. The ZnxV2O5|Zn full cell with the eggshell membrane presented a capacity retention of 91.1% after 2000 cycles at a current density of 5.0 A g−1. In recent work, other proteins such as assembling acetylated protein [64], ovalbumin [65] and zein [66] have also been applied to form a protective layer for achieving dendrite-free Zn metal anodes.

4. Protein-Based Electrolytes for Zn-Based Batteries

4.1. Liquid Electrolytes

Aqueous Zn-ion batteries offer superior safety compared to Li-based systems, owing to the non-toxic nature of both the Zn metal and the aqueous electrolytes [67]. Inspired by the physical properties of natural antifreeze proteins (AFPs), an AFP-mimicking material, oxygen-rich quaternary carbon nanodots (OQCNs), has been synthesized to control ice crystal formation and inhibit recrystallization in the aqueous electrolytes of Zn-ion batteries [68]. Through multi-scale experimental analyses, it was found that OQCNs selectively bind to the prism planes of ice crystals, effectively regulating crystal morphology and suppressing growth rates (Figure 6). This modulation led to the formation of interconnected ion-conducting networks, significantly enhancing ion transport in frozen electrolytes at extremely low temperatures. Molecular dynamics simulations further demonstrated that OQCNs inhibited ice propagation via the Gibbs–Thomson effect from the atomic scale. Utilizing only 5 mg mL−1 of OQCNs in 1 M Zn trifluoromethanesulfonate electrolyte, symmetric Zn|Zn cells achieved extended cycling stability exceeding 1000 h at a current rate of 1 mA cm−2 and deposition capacity of 1 mAh cm−2 under −30 °C. The V2O5|Zn full cells with the electrolyte retained stable performance over 5000 cycles. Meanwhile, NH4+|Zn batteries with the electrolyte maintained 91.48% of their capacity (147.2 mAh g−1) after 90 days at −50 °C and 1 A g−1.

4.2. Gel State Electrolytes

Recent research has explored the use of protein-based gel electrolytes to enhance the biodegradability and biocompatibility of Zn-ion batteries. For instance, Zhou et al. developed a plasticized gelatin–silk electrolyte for Zn-ion batteries [69]. As shown in Figure 7a, silk protein, composed of polypeptide chains rich in amino acids, presented numerous polar side groups after being treated with CaCl2. These chains adopted water-soluble coil and β-sheet conformations with an unfolded structure in solution. Upon mixing gelatin into the silk solution and subsequently removing water, a plasticized film formed and gelatin chains were uniformly embedded within the silk matrix. This integration was reinforced by the robust mechanical stability imparted by the β-sheet domains of silk. When saturated with a liquid electrolyte containing 2 mol L−1 ZnSO4 and 0.1 mol L−1 MnSO4, the resulting gelatin–silk electrolyte exhibits excellent ionic conductivity of 5.68 × 10−3 S cm−1 (Figure 7b). Zn-ion batteries assembled with this electrolyte maintain a stable operating voltage of 1.55 V and demonstrate reliable cycling stability over 100 cycles (Figure 7c). Notably, the battery degrades completely into a protease solution within 45 days, highlighting its environmental sustainability.
In another work, silk fibroin (SF) was introduced into a hydrogel electrolyte of polyacrylamide (PAM) for prolonging the lifespan of Zn-ion batteries [70]. When exposed to solvents, SF underwent a conformational shift from an α-helix to a β-sheet structure, generating a compact and ion-conductive interphase on the Zn surface. The ordered β-sheet network possessed abundant Zn-coordinating polar functional groups that reconstructed a Zn2+ solvation environment, promoting uniform deposition along the (002) crystallographic plane and effectively inhibiting dendrite formation and parasitic reactions. With this SF-introduced hydrogel electrolyte, stable Zn plating/stripping behavior was maintained over 2500 h at a current density of 1 mA cm−2. MnO2|Zn full cells exhibited 93.8% capacity retention after 1500 cycles at 1.0 A g−1. Additionally, the fibrous and flexible architecture offered excellent mechanical resilience, which was promising to be applied in wearable devices. A similar gel electrolyte system was also prepared by combining polypeptides and PAM cross-linked polymer matrix [71]. The peptide gel electrolyte was able to reversibly transform between gel and liquid states, which facilitated the battery assembly and recycling processes of gel-state Zn-ion batteries. Pea protein [72] and α-helical protein extracted from wool [73] have also been applied as the incorporating materials for superelastic or biodegradable gel electrolyte to build long-lifespan and sustainable Zn-ion batteries.

4.3. Solid-State Electrolytes

A green and sustainable solid-state electrolyte, quaternized soybean protein isolate (QSPI, Shansong Biological Products Co., Linyi, China) with the shell of hydrophilic polymer hydroxyethyl cellulose (HEC, Aladdin) (QSPI@HEC), was prepared for application in Zn–air batteries [74,75]. Through a dual cross-linking strategy that combined chemical and thermal methods, QSPI and HEC were integrated into a robust three-dimensional network using a simple solution casting process (Figure 8). Activation energies (Ea) based on the Arrhenius equation indicated that OH− conduction in QSPI@HEC follows the Grotthuss mechanism. Because of the excellent hydrophilicity of HEC, the high ionic conductivity, strong water uptake capacity and interconnected 3D structure of the QSPI@HEC membrane, the assembled Zn–air batteries with QSPI@HEC solid-state electrolyte showed a high open-circuit voltage of 1.54 V, stable rate capability and a peak power density reaching 80 mW cm−2. Moreover, the Zn–air batteries with the QSPI@HEC solid-state electrolyte displayed a long cycling lifespan of approximately 4300 min at 1 mA cm−2, which surpassed those of commercial and SPI-based solid-state electrolytes. Moreover, the flexible battery devices maintained consistent performance under extreme bending up to 180o, demonstrating their suitability for wearable or bendable electronics.

5. Protein-Derived Active Electrodes for Bio-Nanobatteries

A nanoscale energy storage device, bio-nanobattery, was developed using ferritin protein-contained metal chemicals as electrodes [76]. Ferritin (Sigma) has characteristics of spherical protein shells, stability under extreme conditions and the capability to house metal ions in its interior. Ferritins were engineered to contain Fe2+ as the anode material and Co3+ as the cathode material (Figure 9a). An ion-permeable membrane was placed between the ferritin-derived anode and the cathode to build a compact electrochemical cell (Figure 9b). Upon closing the external circuit, electrons transfer from the Fe2+-containing ferritin to the Co3+-containing ferritin, enabling voltage generation of approximately 350–500 mV and efficient charge transfer. Cyclic voltammetry demonstrated that the ferritin electrodes showed stable redox cycling without additional mediators, highlighting the capacity for direct electron conduction from the mineral core through the protein shell to the electrode surface, which was a vital characteristic for practical nano-battery applications (Figure 9c). The initial discharge curve of the bio-nanobattery by time further demonstrated the successful electrochemical energy storage construction (Figure 9d). The ferritin-based nanobattery presents a compelling model for biocompatible, flexible and efficient energy storage at the nanoscale.

6. Organic Radical Batteries

Organic radical batteries are a promising non-alkali metal-ion battery because of their advantages of low cost, absence of strategic metals and faster charging [77,78]. However, the mainstream functional organic molecules, such as 2,2,6,6-tetramethyl-4-piperidine-1-oxyl (TEMPO), in organic radical batteries are non-degradable and bring new environmental problems. To solve this issue, Nguyen et al. reported a degradable and polypeptide-based organic radical battery [79]. Polypeptide-based anode and cathode with redox-active pendant groups were prepared to build electrochemical reactions for all-polypeptide batteries. To synthesize redox-active polypeptides, L-glutamic acid (Glu), a conventional amino acid, was applied as the starting molecule to prepare the viologen-installed polypeptides for the anode and TEMPO-installed polypeptides for the cathode. The synthesis process started from an esterification reaction (add chloro/alkynyl groups on Glu molecules) and cyclization to prepare monomer; thereafter, a polymerization followed by a grating reaction was used to synthesize the polypeptides with desired residues (Figure 10a). During the charging process (Figure 10b left), the nitroxide radical functional groups (N-O· in cathode) lost electrons and were oxidized to oxoammonium cations (+N=O); in contrast, viologen functional groups (Viol2+ at the anode) obtained electrons, and were reduced to their low valence (Viol+·) and then neutral (Viol0) forms. The discharging process (Figure 10b right) possessed the reverse electrochemical reaction of the charging process. These electrochemical reactions were demonstrated by cyclic voltammetry test results in (Figure 10c). The full cells with viol polypeptide-based anode and TEMPO polypeptide-based cathode built 44.5 mA h g−1 based on the amount of anode active materials and still possess electric storage capacity after over 200 cycles (Figure 10d,e). The polypeptide-based full battery also showed excellent degradability in an acid solution with an elevated temperature.
In a recent study, Liu et al. reported a synthetic α-amino acid derivative, cysteine-functionalized natural aloe-emodin (Cys-AE), which significantly enhanced the water solubility and redox reversibility of Cys-AE and was particularly effective in alkaline aqueous organic redox flow batteries [80]. Compared to unmodified aloe-emodin, Cys-AE achieved approximately three times higher aqueous solubility. As a negolyte with an electron concentration of 1.0 M, the Cys-AE-based aqueous organic redox flow battery exhibited a notably low capacity decay rate of just 0.000948% per cycle (0.0438% per day) over 592 cycles, outperforming the batteries based on the original aloe-emodin, which showed a fade rate of 0.00446% per cycle (0.908% per day) over 1564 cycles.

7. Conclusions and Perspectives

This review comprehensively summarizes the protein-based materials and strategies applied in non-alkali metal-ion batteries that include redox flow batteries, Zn–air batteries, and bio-electrochemical systems and organic radical batteries. Protein-based and protein-derived materials exhibit remarkable structural tunability, rich chemical compositions, and intrinsic biocompatibility, which make them excellent candidates for various components in sustainable non-alkali metal ion battery systems.
(1)
Protein-derived biomass carbon materials have attracted attention for their high surface area, porous architecture, and tunable surface chemistry. The biomass carbon derived from proteins such as silk, root nodule protein and zein, has demonstrated excellent performance as electrodes in Zn–air batteries and vanadium redox flow batteries (VRFBs). In Zn–air batteries, nitrogen-doped carbon from silk and protein-rich root nodules have enabled effective oxygen reduction and evolution reactions, offering good catalytic activity and long cycling stability. In VRFBs, carbonized silk and zein-based materials exhibited improved redox kinetics and high electrochemical reversibility, which were attributed to their high nitrogen/oxygen content and interconnected conductive networks.
(2)
Protein-modified active materials have improved battery performance by integrating single-atom catalysts or nanocomposites within protein-derived carbon matrices. Fe-N-C structures derived from pig blood or soybean showed enhanced ORR activity and durability in Zn–air batteries. Additionally, bovine serum albumin (BSA) was used as an exfoliation agent to synthesize MoS2/graphene hybrids, improving their dispersion and electrocatalytic performance. The non-alkali metal ion battery systems with the protein-derived active materials demonstrated improved power densities, voltage outputs, and cycling lifespans.
(3)
Proteins were able to regulate Zn metal anodes to suppress dendrite formation and side reactions with water in aqueous Zn-ion batteries. Collagen hydrolysate (CH) and silk fibroin (SF) have been successfully applied to construct protective films on the Zn metal anode, leading to smoother Zn deposition that improved cycling stability even under high-temperature conditions. These protein molecules contributed to stable solvation structures and ion transport regulation, demonstrating potential scalability from coin cells to large-format batteries.
(4)
Proteins also served as promising candidates in gel electrolytes for biodegradable and flexible Zn-ion batteries. A gelatin-silk protein composite formed a plasticized gel matrix with good ionic conductivity and mechanical robustness. The gel electrolyte delivered consistent voltage output and degraded in enzymatic environments, aligning with growing interest in transient and eco-friendly energy storage technologies.
(5)
Ferritin-based bio-nanobatteries have been developed by employing ferritins loaded with Fe(OH)2 and Co(OH)3 as anode and cathode materials, respectively. These nanoscale batteries generated stable voltage and were fully regenerable. In addition, redox-active polypeptides synthesized from amino acids have been applied as the active materials of anode and cathode of batteries, which offered competitive energy storage capacity and cycling stability while being fully degradable under mild acidic conditions.
In summary, this review highlights the growing versatility and functionality of protein-based materials in energy storage and conversion systems. Protein-based materials offer intrinsic heteroatom-rich chemistry, tunable architecture and strong metal-binding affinities that enhance catalysis, ion/electron transport and electrode stability, leading to the excellent performance of redox flow batteries and Zn-ion batteries. Meanwhile, through pyrolysis, chemical modification or self-assembly, proteins can be transformed into high-performance electrodes, electrocatalysts, electrolytes, separators and protective films. Their natural abundance, biodegradability and structural diversity make them attractive for building low-cost, sustainable and green non-alkali metal ion battery technologies. Furthermore, applying appropriate denaturing methods to precisely control the quaternary structure and exposed functional groups is critical to obtaining the expected protein properties in batteries. Genetically engineering for modifying amino acid sequence and quaternary structure is also promising to generate more attractive proteins with various specific functions. To further improve the performance of batteries, the complex effects of protein in battery systems need to be investigated in depth due to the possible additional side reactions and decomposition during cycling, in addition to the positive impacts. Most importantly, proteins, such as zein and soy protein, are abundant, renewable, and biodegradable, making them promising functional materials for industrial adoption. With standardized sourcing, molecular engineering and hybridization, protein-based battery materials could transition from lab research to commercial energy storage, though stability and quality control remain key challenges.

Author Contributions

Conceptualization, Q.W. and C.W.; investigation, Q.W. and C.W.; resources, W.-H.Z.; writing—original draft preparation, Q.W. and C.W.; writing—review and editing, W.-H.Z.; supervision, C.W. and W.-H.Z.; project administration, W.-H.Z.; funding acquisition, W.-H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by USDA NIFA 2022-67021-38685.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic of protein-based strategies for non-alkali metal-ion batteries.
Figure 1. Schematic of protein-based strategies for non-alkali metal-ion batteries.
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Figure 2. Protein-derived biomass carbon for the electrode for Zn–air batteries. (a) Scanning electron microscopy (SEM) image; (b) High-resolution transmission electron microscopy (HRTEM) image; and (c) high-resolution X-ray photoelectron spectroscopy (XPS) spectrum of N 1s for silk-derived defect-rich and nitrogen-doped nanocarbon electrocatalyst (SilkNC/KB; silk/KB = 1.0; pyrolysis temperature = 1050 °C); (d) Electrochemical oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) performance of SilkNC/KB; (e) galvanostatic discharge–charge cycling curves of the rechargeable Zn–air batteries based on SilkNC/KB catalyst. Reprinted/adapted with permission from Ref. [47]. Copyright 2019, American Chemical Society. (f) Raman patterns of root-nodule-derived carbon that carbonized and pyrolysis at different temperature (RN350-1000, RN350-Z(1-2)-T; T = 700, 800, 900, 1000 °C); (g) Zn–air battery polarization curves and corresponding power density curves using RN350-Z(1-2)-1000 and 20% Pt/C as the cathode [48]. Reprinted/adapted with permission from Ref. [48]. Copyright 2021, Royal Society of Chemistry.
Figure 2. Protein-derived biomass carbon for the electrode for Zn–air batteries. (a) Scanning electron microscopy (SEM) image; (b) High-resolution transmission electron microscopy (HRTEM) image; and (c) high-resolution X-ray photoelectron spectroscopy (XPS) spectrum of N 1s for silk-derived defect-rich and nitrogen-doped nanocarbon electrocatalyst (SilkNC/KB; silk/KB = 1.0; pyrolysis temperature = 1050 °C); (d) Electrochemical oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) performance of SilkNC/KB; (e) galvanostatic discharge–charge cycling curves of the rechargeable Zn–air batteries based on SilkNC/KB catalyst. Reprinted/adapted with permission from Ref. [47]. Copyright 2019, American Chemical Society. (f) Raman patterns of root-nodule-derived carbon that carbonized and pyrolysis at different temperature (RN350-1000, RN350-Z(1-2)-T; T = 700, 800, 900, 1000 °C); (g) Zn–air battery polarization curves and corresponding power density curves using RN350-Z(1-2)-1000 and 20% Pt/C as the cathode [48]. Reprinted/adapted with permission from Ref. [48]. Copyright 2021, Royal Society of Chemistry.
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Figure 3. (a) Field emission transmission electron microscope (FETEM) images and (b) X-ray diffraction (XRD) diffractograms of the silk protein-derived carbon fabrics (SCF-T) prepared at various calcination temperatures. Reprinted/adapted with permission from Ref. [49]. Copyright 2021, Elsevier. SEM images of (c) the pristine twin cocoon, (d) the hydrothermal-treated twin cocoon and (e) the carbonized twin cocoon. Reprinted/adapted with permission from Ref. [50]. Copyright 2019, Elsevier. (f) SEM image of pristine zein powder (upper) and the pristine carbon black (CB) nanoparticles (lower); (g) HR-TEM image of the N-CB catalyst; (h) energy efficiency of the untreated carbon felt (CF), oxidized CF, CB-CF, and N-CB-CF electrodes during the rate capability test. Reprinted/adapted with permission from Ref. [52]. Copyright 2021, Royal Society of Chemistry.
Figure 3. (a) Field emission transmission electron microscope (FETEM) images and (b) X-ray diffraction (XRD) diffractograms of the silk protein-derived carbon fabrics (SCF-T) prepared at various calcination temperatures. Reprinted/adapted with permission from Ref. [49]. Copyright 2021, Elsevier. SEM images of (c) the pristine twin cocoon, (d) the hydrothermal-treated twin cocoon and (e) the carbonized twin cocoon. Reprinted/adapted with permission from Ref. [50]. Copyright 2019, Elsevier. (f) SEM image of pristine zein powder (upper) and the pristine carbon black (CB) nanoparticles (lower); (g) HR-TEM image of the N-CB catalyst; (h) energy efficiency of the untreated carbon felt (CF), oxidized CF, CB-CF, and N-CB-CF electrodes during the rate capability test. Reprinted/adapted with permission from Ref. [52]. Copyright 2021, Royal Society of Chemistry.
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Figure 4. (a) HR-TEM image (the arrows indicated pores), (b) high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image (the green circles indicated Fe sites) and (c) element mapping of Zn/FeSA-PC/950/NH3 catalyst; (d) the corresponding Barrett–Joyner–Halenda (BJH) pore size distributions; (e) the N1s according to various N groups; (f) linear sweep voltammetry (LSV) curves of Zn/FeSA-PC/950/NH3 materials obtained in O2-saturated 0.1 M KOH; (g) the power density plots of Zn–air batteries that used Zn/FeSA-PC/950/NH3 catalyst and commercial Pt/C catalyst as cathode materials. Reprinted/adapted with permission from Ref. [54]. Copyright 2019, Elsevier. SEM images of (h) FeSoy-CNSs-A, (i) NiFe-LDH and (j) NiFe-LDH/FeSoy-CNSs-A. (k) HRTEM images of NiFe-LDH/FeSoy-CNSs-A. (l) Raman mapping of NiFe-LDH/FeSoy-CNSs-A. (m) Galvanostatic discharge–charge cycling curves using NiFe-LDH/FeSoy-CNSs-A and Pt/C + RuO2 catalysts at 5 mA cm−2 with 10-min cycle. Reprinted/adapted with permission from Ref. [55]. Copyright 2021, Springer.
Figure 4. (a) HR-TEM image (the arrows indicated pores), (b) high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image (the green circles indicated Fe sites) and (c) element mapping of Zn/FeSA-PC/950/NH3 catalyst; (d) the corresponding Barrett–Joyner–Halenda (BJH) pore size distributions; (e) the N1s according to various N groups; (f) linear sweep voltammetry (LSV) curves of Zn/FeSA-PC/950/NH3 materials obtained in O2-saturated 0.1 M KOH; (g) the power density plots of Zn–air batteries that used Zn/FeSA-PC/950/NH3 catalyst and commercial Pt/C catalyst as cathode materials. Reprinted/adapted with permission from Ref. [54]. Copyright 2019, Elsevier. SEM images of (h) FeSoy-CNSs-A, (i) NiFe-LDH and (j) NiFe-LDH/FeSoy-CNSs-A. (k) HRTEM images of NiFe-LDH/FeSoy-CNSs-A. (l) Raman mapping of NiFe-LDH/FeSoy-CNSs-A. (m) Galvanostatic discharge–charge cycling curves using NiFe-LDH/FeSoy-CNSs-A and Pt/C + RuO2 catalysts at 5 mA cm−2 with 10-min cycle. Reprinted/adapted with permission from Ref. [55]. Copyright 2021, Springer.
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Figure 5. (a) SEM images of collagen hydrolysate coated on absorbed glass mat (CH@AGM); (b) voltammetry of Zn|AGM + CH@AGM|Zn and Zn|AGM|Zn cells in the 1 M ZnSO4 electrolyte at a scan rate of 1 mV s−1; (c,f) mechanistic sketches of the effect of surface conduction on metal electrodeposition in a charged pore; SEM images of the Zn anode in Zn|AGM|Zn cell after 10 min of chronoamperometry (d) with and (e) without CH in the aqueous electrolyte; (g) galvanostatic Zn plating/stripping voltage profiles for symmetric Zn|AGM + CH@AGM|Zn and Zn|AGM|Zn cells at a capacity of 1 mAh cm−2 and a current density of 1 mA cm−2; (h) cycling performance of the discharge capacity and Coulombic efficiency of LMO|AGM + CH@AGM|Zn and LMO|AGM|Zn cells with the 3.6 mAh cm−2 cathode at a rate of 1 C. Reprinted/adapted with permission from Ref. [57]. Copyright 2020, American Association for the Advancement of Science. (i) Pure ZnSO4 and (k) ZnSO4 + 0.5SF electrolytes with 100 cycles at 1 mA cm−2 and 1 mAh cm−2. Scale bars: 20 μm; (j) cycling performance of Zn||KVO full cells in ZnSO4 and ZnSO4 + 0.5SF electrolytes at a high current density of 3 A g−1. Reprinted/adapted with permission from Ref. [58]. Copyright 2022, American Chemical Society.
Figure 5. (a) SEM images of collagen hydrolysate coated on absorbed glass mat (CH@AGM); (b) voltammetry of Zn|AGM + CH@AGM|Zn and Zn|AGM|Zn cells in the 1 M ZnSO4 electrolyte at a scan rate of 1 mV s−1; (c,f) mechanistic sketches of the effect of surface conduction on metal electrodeposition in a charged pore; SEM images of the Zn anode in Zn|AGM|Zn cell after 10 min of chronoamperometry (d) with and (e) without CH in the aqueous electrolyte; (g) galvanostatic Zn plating/stripping voltage profiles for symmetric Zn|AGM + CH@AGM|Zn and Zn|AGM|Zn cells at a capacity of 1 mAh cm−2 and a current density of 1 mA cm−2; (h) cycling performance of the discharge capacity and Coulombic efficiency of LMO|AGM + CH@AGM|Zn and LMO|AGM|Zn cells with the 3.6 mAh cm−2 cathode at a rate of 1 C. Reprinted/adapted with permission from Ref. [57]. Copyright 2020, American Association for the Advancement of Science. (i) Pure ZnSO4 and (k) ZnSO4 + 0.5SF electrolytes with 100 cycles at 1 mA cm−2 and 1 mAh cm−2. Scale bars: 20 μm; (j) cycling performance of Zn||KVO full cells in ZnSO4 and ZnSO4 + 0.5SF electrolytes at a high current density of 3 A g−1. Reprinted/adapted with permission from Ref. [58]. Copyright 2022, American Chemical Society.
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Figure 6. Mechanism of bioinspired synthetic antifreeze proteins (AFPs) mimics of oxidized quasi-carbon nitride quantum dots (OQCNs) for ice growth inhibition and the schematic diagram of the low-temperature operation of antifreeze aqueous Zn-ion battery and functions of OQCNs. Reprinted/adapted with permission from Ref. [68]. Copyright 2025, Wiley.
Figure 6. Mechanism of bioinspired synthetic antifreeze proteins (AFPs) mimics of oxidized quasi-carbon nitride quantum dots (OQCNs) for ice growth inhibition and the schematic diagram of the low-temperature operation of antifreeze aqueous Zn-ion battery and functions of OQCNs. Reprinted/adapted with permission from Ref. [68]. Copyright 2025, Wiley.
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Figure 7. Gel electrolyte for Zn-ion batteries. (a) Schematic diagram of fabrication of gelatin–silk fibroin electrolytes; (b) Stress–strain curves of silk fibroin films (water content: 12%) with different gelatin weight ratios; (c) Long-term cycling performance and Coulombic efficiency of fiber-shaped TZIBs at 61.6 mA g−1. Reprinted/adapted with permission from Ref. [69]. Copyright 2021, Elsevier.
Figure 7. Gel electrolyte for Zn-ion batteries. (a) Schematic diagram of fabrication of gelatin–silk fibroin electrolytes; (b) Stress–strain curves of silk fibroin films (water content: 12%) with different gelatin weight ratios; (c) Long-term cycling performance and Coulombic efficiency of fiber-shaped TZIBs at 61.6 mA g−1. Reprinted/adapted with permission from Ref. [69]. Copyright 2021, Elsevier.
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Figure 8. Preparation of quaternized soybean protein isolate with shell of hydrophilic polymer hydroxyethyl cellulose (QSPI@HEC) and the ion exchange process. Reprinted/adapted with permission from Ref. [74]. Copyright 2024, American Chemical Society.
Figure 8. Preparation of quaternized soybean protein isolate with shell of hydrophilic polymer hydroxyethyl cellulose (QSPI@HEC) and the ion exchange process. Reprinted/adapted with permission from Ref. [74]. Copyright 2024, American Chemical Society.
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Figure 9. (a) Schematic of a bio-nanobattery using ferritin with Fe(OH)2 anode and Co(OH)3 cathode, immersed in 0.05 M buffer (pH 7.0–9.0, 0.10 M NaCl). (b) Multilayered ferritin battery with alternating charged layers (blue: anode, red: cathode); yellow membrane optional. SEM and AFM images show five ferritin layers. (c) Voltage cycling at 100 mV·s−1 in 0.05 M MOPS (pH = 7.0) with 0.05 M thioglycolic acid (TGA). (d) Discharge curve of a cell with Fe(OH)2 and Co(OH3 ferritins on gold electrodes (pH = 8.0; drain rate = 100 nA). Reprinted/adapted with permission from Ref. [76]. Copyright 2012, Hindawi.
Figure 9. (a) Schematic of a bio-nanobattery using ferritin with Fe(OH)2 anode and Co(OH)3 cathode, immersed in 0.05 M buffer (pH 7.0–9.0, 0.10 M NaCl). (b) Multilayered ferritin battery with alternating charged layers (blue: anode, red: cathode); yellow membrane optional. SEM and AFM images show five ferritin layers. (c) Voltage cycling at 100 mV·s−1 in 0.05 M MOPS (pH = 7.0) with 0.05 M thioglycolic acid (TGA). (d) Discharge curve of a cell with Fe(OH)2 and Co(OH3 ferritins on gold electrodes (pH = 8.0; drain rate = 100 nA). Reprinted/adapted with permission from Ref. [76]. Copyright 2012, Hindawi.
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Figure 10. Polypeptide organic radical batteries [79]. (a) Schematics of a polypeptide-based organic radical battery and the reactions that occur during charging and discharging are shown on the left and right, respectively; (b) Synthesis strategy of redox-active polypeptides; (c) cyclic voltammograms, (d) charge–discharge curves solid, charge; dashed, discharge) and (e) cycling response of the viol-Cl–biTEMPO polypeptide full cell; A viol-Cl polypeptide composite electrode was separated from a biTEMPO polypeptide composite electrode by filter paper soaked in 0.5 M TBACF3SO3 in propylene carbonate. The composite electrodes were composed of 30 wt% active polypeptide, 60 wt% carbon black and 10 wt% polyvinylidene fluoride on ITO-coated glass. Reprinted/adapted with permission from Ref. [79]. Copyright 2020, American Association for the Advancement of Science.
Figure 10. Polypeptide organic radical batteries [79]. (a) Schematics of a polypeptide-based organic radical battery and the reactions that occur during charging and discharging are shown on the left and right, respectively; (b) Synthesis strategy of redox-active polypeptides; (c) cyclic voltammograms, (d) charge–discharge curves solid, charge; dashed, discharge) and (e) cycling response of the viol-Cl–biTEMPO polypeptide full cell; A viol-Cl polypeptide composite electrode was separated from a biTEMPO polypeptide composite electrode by filter paper soaked in 0.5 M TBACF3SO3 in propylene carbonate. The composite electrodes were composed of 30 wt% active polypeptide, 60 wt% carbon black and 10 wt% polyvinylidene fluoride on ITO-coated glass. Reprinted/adapted with permission from Ref. [79]. Copyright 2020, American Association for the Advancement of Science.
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Table 1. Protein-derived biomass carbon as the electrodes for non-alkali metal-ion batteries [47,48,49,50,51,52].
Table 1. Protein-derived biomass carbon as the electrodes for non-alkali metal-ion batteries [47,48,49,50,51,52].
Protein TypeCarbon TypeSystem TypeElectrochemical PerformanceElectrolyteCounter ElectrodeReference
SilkDefect-rich and N-doped carbonZn–airVoltage gap = 1.39 V, voltaic efficiency = 41.3% after 100 cycles6.0 M KOH + 0.2 M ZnAC, PVA aqueous gelZn[47]
Root noduleFe, Mo, S, N self-doped porous carbonZn–airHalf-wave potentials are 0.723 V (vs. RHE) in 0.1 M HClO4 and 0.868 V and 0.1 M KOH solution6 M KOH + 0.2 M Zn(CH3CO2)2Zn[48]
Fuel cellFlow rate of H2 was 10 mL min−1, 17.6 mW cm−2 with an open-circuit voltage of 0.966 VH2 | airGraphite
SilkCarbon fabricsAll-vanadium redox flow batteriesEnergy efficiency = 86.8%1.6 M VOSO4 in 4 M H2SO4 solutionSymmetrical[49]
Twin cocoonSelf-standing monolithic carbonAll-vanadium redox flow batteries50% redox potential decrease and 192% diffusion slope increase1.0 M VOSO4 + 3.0 M H2SO4Pt, Ag/AgCl[50]
PyroproteinCarbon felts@ pyroproteinAll-vanadium redox flow batteriesΔEp = 0.17 V, energy efficiency = 90% at 40 mA cm−20.1 M VOSO4 in 2 M H2SO4Three electrodes[51]
ZeinZein-coated carbon blackAll-vanadium redox flow batteriesEnergy efficiency = 85.2% after 100th cyclesPositive: 2 M VOSO4 in 3 M H2SO4
Negative: 2 M VOSO4 in 3 M H2SO4		Symmetrical[52]
Note: Symmetrical indicates that both electrodes are the same electrode.
Table 2. Protein-derived active materials for non-alkali metal-ion batteries [54,55,56].
Table 2. Protein-derived active materials for non-alkali metal-ion batteries [54,55,56].
Protein TypeElectrodeSystemsElectrochemical PerformanceSeparatorElectrolyteCounter ElectrodeReference
Pig blood2D Zn-Fe single-atom porous carbon catalyst Zn–air 220 mW cm−2/6.0 M KOHZn[54]
AEMFCs352 mW cm−2FAA-3-20 (coating toward cathode)H2/O2Symmetrical gas diffusion layer
Bovine serum albuminProtein-coated MoS2/Gr nanosheetZn–air130 W h kg−1,
OCV = 1.4 V		Whatman filter paper4 M KOHZn[56]
SoybeanNiFe-LDH nanowalls anchored on Fe-N-C matrixZn–airOER (Ej=10 = 1.53 V vs. RHE) and ORR (E1/2 = 0.91 V vs. RHE)/6.0 M KOH + 0.2 M ZnACZn[55]
Abbreviations: AEMFCs: anion exchange membrane fuel cells; Whatman: glass microfiber filter; FAA-3-20: a non-reinforced anion exchange membrane; Gr: graphene; OCV: open circuit potential; NiFe-LDH: NiFe-layered double hydroxide; OER: oxygen evolution reaction; ORR: oxygen reduction reaction; RHE: reversible hydrogen electrode. “/” indicates that the component did not exist in the related systems or was not mentioned in the literature.
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Wang, Q.; Wang, C.; Zhong, W.-H. Protein-Based Strategies for Non-Alkali Metal-Ion Batteries. Batteries 2025, 11, 318. https://doi.org/10.3390/batteries11090318

AMA Style

Wang Q, Wang C, Zhong W-H. Protein-Based Strategies for Non-Alkali Metal-Ion Batteries. Batteries. 2025; 11(9):318. https://doi.org/10.3390/batteries11090318

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Wang, Qian, Chenxu Wang, and Wei-Hong Zhong. 2025. "Protein-Based Strategies for Non-Alkali Metal-Ion Batteries" Batteries 11, no. 9: 318. https://doi.org/10.3390/batteries11090318

APA Style

Wang, Q., Wang, C., & Zhong, W.-H. (2025). Protein-Based Strategies for Non-Alkali Metal-Ion Batteries. Batteries, 11(9), 318. https://doi.org/10.3390/batteries11090318

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