Search Results (21)

Efficient electrocatalysts for the oxygen reduction reaction (ORR) are essential for numerous energy storage and conversion systems, including zinc–air batteries and fuel cells. Cutting-edge Pt/C catalysts remain the most efficient ORR catalysts to date; however, their high cost and inadequate stability impede their use in commercial devices. Recently, transition metal-based electrocatalysts are being pursued as ideal alternatives for cost-effective and efficient materials with a promising future. This review provides an in-depth analysis of the principles, synthesis, and electrocatalytic assessment of noble metal and transition metal-based catalysts derived from diverse gel precursors, including hydrogels, aerogels, xerogels, metal–organic gels, and metal aerogels. Electrocatalysts derived from gel precursors have garnered significant interest due to their superior physicochemical properties, including an exceptionally high surface area, adjustable porosity, adaptability, and scalability. Catalysts obtained from gel precursors offer numerous advantages over conventional catalyst synthesis methods, including the complete utilization of precursors, precise control over surface area and porosity, and uniform distribution of ORR active sites. Among the various types, metal aerogels are distinguished as the superior catalysts, exceeding the Department of Energy’s (DoE) 2025 targets for the mass and specific activities of ORR catalysts. In contrast, hydrogel- and aerogel-derived catalysts excel in terms of ORR activity, specific surface area, and the potential to incorporate high loadings of single-atom catalysts composed of transition metals. Ultimately, we unequivocally categorized the electrocatalysts into high-, moderate-, and low-performance tiers, identifying the most promising catalyst candidate within each gel classification. Concluding insights, future outlooks, and recommendations were provided for the advancement of cost-effective, scalable electrocatalysts derived from gels for fuel cells and zinc–air batteries. Full article

We report the results of a zinc oxide (ZnO) low-power microsensor for sub-ppm detection of NO₂ and H₂S in air at 200 °C. NO₂ emission is predominantly produced by the combustion processes of fossil fuels, while coal-fired power plants are the main emitter of H₂S. Fossil fuels (oil, natural gas, and coal) combined contained 74% of USA energy production in 2023. It is foreseeable that the energy industry will utilize fossil-based fuels more in the ensuing decades despite the severe climate crises. Precise NO₂ and H₂S sensors will contribute to reducing the detrimental effect of the hazardous emission gases, in addition to the optimization of the combustion processes for higher output. The fossil fuel industry and solid-oxide fuel cells (SOFCs) are exceptional examples of energy conversion–production technologies that will profit from advances in H₂S and NO₂ sensors. Porosity and surface activity of metal oxide semiconductor (MOS)-based sensors are both vital for sensing at low temperatures. Oxygen vacancies (${\mathbf{V}}_{\mathbf{O}}^{••}$) act as surface active sites for target gases, while porosity enables target gases to come in contact with a larger MOS area for sensing. We were able to create an open porosity network throughout the ZnO microstructure and simultaneously achieve an abundance of oxygen vacancies by using a heat treatment procedure. Surface chemistry and oxygen vacancy content in ZnO were examined using XPS and AES. SEM was used to understand the morphology of the unique characteristics of distinctive grain growth during heat treatment. Electrical resistivity measurements were completed. The valance band was examined by UPS. The Engineered Porosity approach allowed the entire ZnO to act as an open surface together with the creation of abundant oxygen vacancies (${\mathbf{V}}_{\mathbf{O}}^{••}$). NO₂ detection is challenging since both oxygen (O₂) and NO₂ are oxidizing gases, and they coexist in combustion environments. Engineered porosity ZnO microsensor detected sub-ppm NO₂ under O₂ interference, which affects mimicking realistic sensor operation conditions. Engineered porosity ZnO performed better than the previous literature findings for H₂S and NO₂ detection. The exceptionally high sensor response is attributed to the high number of oxygen vacancies (${\mathit{V}}_{\mathit{O}}^{••}$) and porosity extending through the thickness of the ZnO with a high degree of tortuosity. These features enhance gas adsorption and diffusion via porosity, leading to high sensor response. Full article

Microbial fuel cell (MFC) can degrade pesticide wastewater and recovery energy simultaneously, and the activated carbon (AC) air cathode has great prospects for practical application. However, insufficient active sites and the limitation of multi-step electron transfer for oxygen reduction reaction (ORR) requires that AC should be modified by highly efficient electrocatalysts. Herein, busing the confinement effect of carbon-encapsulated metal and hollow carbon, we designed a unique ORR catalyst of Fe-Fe₃O₄-NC through utilizing the 2D leaf-like nanoplates of Zn-ZIF-L to load Prussian blue (PB) particles. The volatilization of low-boiled Zn and the catalysis of iron compounds led to the formation of confined walls of hollow carbon shell and carbon-encapsulated Fe/Fe₃O₄ particles on N-doped carbon substrate. Multivalent iron, a large surface area (368.11 m²·g⁻¹), N doping, a heterojunction interface, and the confinement effect provided all the Fe-Fe₃O₄-NC-modified AC air cathodes with excellent ORR activity. The optimal samples of AC-Fe-Fe₃O₄-NC-3 achieved a peak power density of 1213.8 mW·m⁻², demonstrating a substantial 82.8% increase over that of the bare AC. Furthermore, its efficiency in glyphosate removal reached 80.1%, surpassing the 23.2% of the bare AC. This study offers new ideas in constructing composite confined structures and the as-designed Fe-Fe₃O₄-NC is a promising modification candidate for the commercial adoption of AC air cathodes. Full article

Cadmium (Cd) is a pervasive toxic metal, present in most food types, cigarette smoke, and air. Most cells in the body will assimilate Cd, as its charge and ionic radius are similar to the essential metals, iron, zinc, and calcium (Fe, Zn, and Ca). Cd preferentially accumulates in the proximal tubular epithelium of the kidney, and is excreted in urine when these cells die. Thus, excretion of Cd reflects renal accumulation (body burden) and the current toxicity of Cd. The kidney is the only organ other than liver that produces and releases glucose into the circulation. Also, the kidney is responsible for filtration and the re-absorption of glucose. Cd is the least recognized diabetogenic substance although research performed in the 1980s demonstrated the diabetogenic effects of chronic oral Cd administration in neonatal rats. Approximately 10% of the global population are now living with diabetes and over 80% of these are overweight or obese. This association has fueled an intense search for any exogenous chemicals and lifestyle factors that could induce excessive weight gain. However, whilst epidemiological studies have clearly linked diabetes to Cd exposure, this appears to be independent of adiposity. This review highlights Cd exposure sources and levels associated with diabetes type 2 and the mechanisms by which Cd disrupts glucose metabolism. Special emphasis is on roles of the liver and kidney, and cellular stress responses and defenses, involving heme oxygenase-1 and -2 (HO-1 and HO-2). From heme degradation, both HO-1 and HO-2 release Fe, carbon monoxide, and a precursor substrate for producing a potent antioxidant, bilirubin. HO-2 appears to have also anti-diabetic and anti-obese actions. In old age, HO-2 deficient mice display a symptomatic spectrum of human diabetes, including hyperglycemia, insulin resistance, increased fat deposition, and hypertension. Full article

Highly active and cost-efficient electrocatalysts for oxygen reduction reaction (ORR) are significant for developing renewable energy conversion devices. Herein, a nanocomposite Fe/ZnS-SNC electrocatalyst with an FeS and ZnS heterojunction on N,S-codoped carbon has been fabricated via a facile one-step sulfonating of the pre-designed Zn- and Fe-organic frameworks. Benefitting from the electron transfer from FeS to adjacent ZnS at the heterointerfaces, the optimized Fe/ZnS-SNC900 catalyst exhibits excellent ORR performances, featuring the half-wave potentials of 0.94 V and 0.81 V in alkaline and acidic media, respectively, which is competitive with the commercial 20 wt.% Pt/C (0.87 and 0.76 V). The flexible Zn-air battery equipping Fe/ZnS-SNC900 affords a higher open-circuit voltage (1.45 V) and power density of 30.2 mW cm⁻². Fuel cells assembled with Fe/ZnS-SNC900 as cathodic catalysts deliver a higher power output of 388.3 and 242.8 mW cm⁻² in H₂-O₂ and -air conditions. This work proposes advanced heterostructured ORR electrocatalysts that effectively promote renewable energy conversions. Full article

Zn–air batteries are becoming the promising power source for small electronic devices and electric vehicles. They provide a relatively high specific energy density at relatively low cost. This review presents exciting advances and challenges related to the development of molecular catalysts for cathode reactions in Zn–air batteries. Bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play the main role in improving performance of reversible fuel cell and metal–air batteries. The catalyst development strategies are reviewed, along with strategies to enhance catalyst performance by application of magnetic field. Proper design of bifunctional molecular ORR/OER catalysts allows the prolongment of the battery reversibility to a few thousand cycles and reach of energy efficiencies of over 70%. Full article

There is an urgent need to design and synthesize non-noble metal electrocatalysts (NNMEs) for the replacement of platinum-based electrocatalysts to enhance the sluggish oxygen reduction reaction (ORR) for Zn–air batteries and fuel cells. Herein, Fe-N,S-C materials were fabricated through two steps: first, reprecipitating hemin by adjusting the pH and, then, decorating it with melamine and cysteine in the presence of Zn²⁺. The resulting Fe-N,S-C-950 (Zn) was prepared after pyrolysis at 950 °C. Using this method, abundant iron-based active species with good dispersion were obtained. The fabrication of more micropores in Fe-N,S-C-950 (Zn) plays a positive role in the improvement of ORR activity. On comparison, Fe-N,S-C-950 (Zn) outperforms Fe-N,S-C-950 and Fe-N-C-950 (Zn) with respect to the ORR due to its larger specific surface area, porous structure, multiple iron-based active sites and N- and S-doped C. Fe-N,S-C-950 (Zn) achieves outstanding ORR performances, including a half-wave potential (E_1/2) of 0.844 V and 0.715 V versus a reversible hydrogen electrode (RHE) in 0.1 M KOH and 0.1 M HClO₄ solution, respectively. In addition, Fe-N,S-C-950 (Zn) shows an outstanding Zn–air battery performance with an open-circuit voltage (OCV) of 1.450 V and a peak power density of 121.9 mW cm⁻², which is higher than that of 20 wt% Pt/C. As a result, the as-prepared electrocatalyst in this work shows the development of the Zn-assisted strategy combined with the assembly of porphyrins as NNMEs for the enhancement of the ORR in both alkaline and acidic solutions. Full article

The development of efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) to replace Pt-based methods is crucial for the applications of fuel cells and metal–air batteries. In this study, a bimetallic M-N-C catalyst with highly dispersed dual-atom Fe/Mn-Nx sites immobilized on N-doped bamboo-like carbon nanotubes is prepared by the ball-milling and calcination of dual-MOFs as precursors. The rich N-doping and abundant M–Nx species contribute to the excellent intrinsic ORR activity of the catalyst, and the unique bamboo-like nanotubes morphology is beneficial for facilitating electron transfer and mass transport while simultaneously enabling the exposure of active sites. As expected, the optimized Z-Fe1Mn1-NC catalyst exhibits efficient ORR activity with a half-wave potential (E_1/2) of 0.80 V in acid and 0.82 V in alkaline, and a higher electrochemical stability with the current density maintained at 91% (in 0.1 M KOH) and 86% (0.1 M HClO₄) of its initial current density after 15 h of a chronoamperometric test at a high potential of 0.7 V. When further applied to Zn–air batteries, the catalyst also delivers a high open-circuit voltage, large power density, and outstanding rate performance. This work provides a novel means of designing dual metal M–Nx site-based M-N-C catalysts for ORR sustainable energy applications. Full article

Improving the ionic conductivity and slow oxygen reduction electro-catalytic activity of reactions occurring at low operating temperature would do wonders for the widespread use of low-operating temperature ceramic fuel cells (LT-CFCs; 450–550 °C). In this work, we present a novel semiconductor heterostructure composite made of a spinel-like structure of Co_0.6Mn_0.4Fe_0.4Al_1.6O₄ (CMFA) and ZnO, which functions as an effective electrolyte membrane for solid oxide fuel cells. For enhanced fuel cell performance at sub-optimal temperatures, the CMFA–ZnO heterostructure composite was developed. We have shown that a button-sized SOFC fueled by H₂ and ambient air can provide 835 mW/cm² of power and 2216 mA/cm² of current at 550 °C, possibly functioning down to 450 °C. In addition, the oxygen vacancy formation energy and activation energy of the CMFA–ZnO heterostructure composite is lower than those of the individual CMFA and ZnO, facilitating ion transit. The improved ionic conduction of the CMFA–ZnO heterostructure composite was investigated using several transmission and spectroscopic measures, including X-ray diffraction, photoelectron, and UV–visible spectroscopy, and density functional theory (DFT) calculations. These findings suggest that the heterostructure approach is practical for LT-SOFCs. Full article

Oxygen-ionic and proton-conducting oxides are widely studied materials for their application in various electrochemical devices such as solid oxide fuel cells and electrolyzers. Rare earth oxides are known as a class of ionic conductors. In this paper, La₂ZnNdO_5.5 and its Ca-doped derivatives La₂Nd_0.9Ca_0.1ZnO_5.45 and La₂ZnNd_0.9Ca_0.1O_5.45 were obtained by a solid-state reaction route. Phase composition, lattice parameters, and hydration capability were investigated by X-ray diffraction and thermogravimetric analyses. The conductivities of these materials were measured by the electrochemical impedance spectroscopy technique in dry (pH₂O = 3.5 × 10⁻⁵ atm) and wet (pH₂O = 2 × 10⁻² atm) air. All phases crystallized in a trigonal symmetry with P3m1 space group. The conductivity difference between undoped and calcium-doped samples is more than two orders of magnitude due to the appearance of oxygen vacancies during acceptor doping, which are responsible for a higher ionic conductivity. The La₂Nd_0.9Ca_0.1ZnO_5.45 sample shows the highest conductivity of about 10⁻³ S∙cm⁻¹ at 650 °C. The Ca-doped phases are capable of reversible water uptake, confirming their proton-conducting nature. Full article

Mixed metallic oxides are getting increasing attention as novel electrode materials for energy conversion devices. However, low mixed ionic-electronic conductivity and high operating temperature hamper the practical applications of these devices. This study reports an effective strategy to improve the conductivity and performance of the fuel cell at low temperature by partially incorporating graphene in the Li_0.1Cu_0.2Zn_0.7-oxide (LCZ) composite. The proposed cathode material is synthesized via the cost effective conventional solid-state route. Graphene incorporated LCZ shows excellent performance, which is attributed to the favorable charge transport paths offering low area-specific resistance. An X-ray diffractometer (XRD) and scanning electron microscope (SEM) are employed for microstructural and surface morphological analyses, respectively. Electrical conductivities of all the materials are determined by the DC four probe method, and interestingly, LCZ-1.5% graphene exhibits an excellent conductivity of 3.5 S/cm in air atmosphere at a temperature of 450 °C with a minimum value of 0.057 Ωcm² area-specific resistance (ASR) that demonstrates significantly good performance. Moreover, the three-layer fuel cell device is fabricated using sodium carbonated Sm_0.2Ce_0.8O (NSDC) as an electrolyte, which can operate at low temperatures exhibiting open circuit voltage 0.95 V and shows a peak power density, i.e., 267.5 mW/cm² with hydrogen as the fuel. Full article

Fuel electrode-supported tubular protonic ceramic cells (FETPCCs) based on the BaZr_0.4Ce_0.4Y_0.15Zn_0.05O_3−δ (BZCYZ) membrane electrolyte was fabricated through a two-step method, in which the polyporous electrode-support tube was prepared with a traditional slip casting technique in a plaster mold, and the BZCYZ membrane was produced by a dip-coating process on the outside surface of the electrode-support tube. The dense thin-film electrolyte of BZCYZ with a thickness of ~25 μm was achieved by cofiring the fuel electrode support and electrolyte membrane at 1450 °C for 6 h. The electrochemical performances of the FETPCCs were tested under different solid oxide cell modes. In protonic ceramic fuel cell (PCFC) mode, the peak power densities of the cell reached 151–191 mW·cm⁻² at 550–700 °C and exhibited relatively stable performance during continuous operation over 100 h at 650 °C. It was found that the major influence on the performance of tubular PCFC was the resistance and cathode current collectors. Additionally, in protonic ceramic electrolysis cell (PCEC) mode, the current densities of 418–654 mA·cm⁻² were obtained at 600–700 °C with the applied voltage of 2.0 V when exposed to 20% CO₂–80% H₂ and 3% H₂O/air. Using distribution of relaxation time analysis, the electrolytic rate-limiting step of the PCEC model was determined as the adsorption and dissociation of the gas on the electrode surface. Full article

Integrating a photoelectrode into a zinc-air battery is a promising approach to reducing the overpotential required for charging a metal-air battery by using solar energy. In this work, a photo-fuel cell employing a Nb₂O₅/CdS photoanode and a Zn foil as a counter-electrode worked as a photoelectrochemical battery that saves up to 1.4 V for battery charging. This is the first time a Nb₂O₅-based photoelectrode is reported as a photoanode in a metal-air battery, and the achieved gain is one of the top results reported so far. Furthermore, the cell consumed an organic fuel, supporting the idea of using biomass wastes as a power source for sunlight-assisted charging of metal-air batteries. Thus, this device provides additional environmental benefits and contributes to technologies integrating solar energy conversion and storage. Full article

Rational design of cost-effective and efficient bifunctional oxygen electrocatalysts for sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently desired for rechargeable metal–air batteries and regenerative fuel cells. Here, the Fe₃C nanoparticles encapsulated in N and F codoped and simultaneously etched graphene/CNTs architecture catalyst (Fe₃C@N-F-GCNTs) was synthesized by a simple yet cost-effective strategy. The as-prepared Fe₃C@N-F-GCNTs exhibited excellent ORR and OER performances, with the ORR half-wave potential positive than that of Pt/C by 14 mV, and the OER overpotential lowered to 432 mV at the current density of 10 mA·cm⁻². In addition, the ΔE value (oxygen electrode activity parameter) increased to 0.827 V, which is comparable to the performance of the best nonprecious metal catalysts reported to date. When it was applied in a Zn–air battery as a cathode, it achieved a peak power density of 130 mW·cm⁻², exhibiting the potential for large-scale applications. Full article

Proton-conducting solid–oxide fuel cell (H-SOFC) is an alternative promising low-temperature electrochemical cell for renewable energy, but the performance is insufficient because of the low activity of cathode materials at low temperatures. A layered perovskite oxide PrBaFe_1.9Zn_0.1O_5+δ (PBFZ) was synthesized and investigated as a promising cathode material for low-temperature H-SOFC. Here, the partial substitution of Fe by Zn further enhances the electrical conductivity and thermal compatibility of PrBaFe₂O_5+δ (PBF). The PBFZ exhibits improved conductivity in the air at intermediate temperatures and good chemical compatibility with electrolytes. The oxygen vacancy formed at the PBFZ lattice due to Zn doping enhances proton defects, resulting in an improved performance by extending the catalytic sites to the whole cathode area. A single cell with a Ni-BZCY anode, PBFZ cathode, and BaZr_0.7Ce_0.2Y_0.1O_3-δ (BZCY) electrolyte membrane was successfully fabricated and tested at 550–700 °C. The maximum power density and R_p were enhanced to 513 mW·cm⁻² and 0.3 Ω·cm² at 700 °C, respectively, due to Zn doping. Full article