Novel Flexible Proton-Conducting Gelatin-Based Green Membranes for Fuel Cell Applications and Flexible Electronics

Abstract

Natural polymers, such as gelatin, offer a sustainable, green, and versatile alternative for developing proton exchange membranes in low-temperature fuel cell applications. They provide a balance of biocompatibility, flexibility, and ionic conductivity. In this work, gelatin-based composite membranes are reported. The membranes were fabricated and modified with various additives, including ionic liquids (ILs), polyethylene glycol (PEG), and glycerol, to enhance their electrochemical and mechanical properties. The proton conductivity of the pure gelatin membrane was relatively low at 1.0368 × 10⁻⁴ Scm⁻¹; however, the incorporation of IL ([DEMA][OMs]) significantly improved it, with the gelatin/0.2 g IL membrane achieving the highest conductivity of 4.181 × 10⁻⁴ Scm⁻¹. The introduction of PEG and glycerol also contributed to enhanced conductivity and flexibility. The water uptake analysis revealed that IL-containing membranes exhibited superior hydration properties, with the highest water uptake recorded for the gelatin/0.2 g glycerol/0.2 g IL membrane, which was found to be very high (906.55%). The results showed that the combination of IL and PEG provided enhanced proton transport and mechanical stability (as examined visually), making these membranes promising candidates for fuel cell applications. Therefore, this study underscores the importance of bio-based materials by utilizing gelatin as a sustainable, biodegradable polymer, supporting the transition toward greener energy materials. The findings demonstrate that modifying gelatin with conductivity-enhancing and plasticizing agents can significantly improve its performance, paving the way for bio-based proton exchange membranes with improved efficiency and durability.

1. Introduction

Fuel cells represent a promising clean energy technology due to their high efficiency, low emissions, and ability to utilize renewable fuel sources [1]. These electrochemical devices convert chemical energy directly into electrical energy through redox reactions. Therefore, this eliminates the need for intermediate combustion processes and significantly reduces greenhouse gas emissions [2]. Among the different types of fuel cells, proton exchange membrane fuel cells (PEMFCs) are particularly advantageous for portable automotive and stationary applications due to their compact design [3], rapid start-up time [4], and operational safety at moderate conditions [5]. However, the performance and durability of these fuel cells heavily rely on the properties of the membrane, which acts as the proton-conducting medium, facilitating ion transport while preventing fuel crossover and undesired electronic conduction in the form of electron leakage that can compromise cell efficiency [6,7]. Developing efficient, durable, and cost-effective membrane materials remains a critical challenge in advancing fuel cell technology.

Both synthetic and natural polymers have been extensively explored for membrane applications in fuel cells due to their ability to provide mechanical strength, ion conductivity, and chemical stability [8,9,10]. Synthetic polymers such as perfluorosulfonic acid (PFSA)-based membranes, including Nafion, are widely regarded as the benchmark due to their exceptional proton conductivity and chemical robustness under operating conditions [11]. However, the high production cost, limited thermal stability, and environmental concerns associated with fluorinated polymers have led to increasing interest in developing sustainable alternatives [12,13]. In contrast, natural polymers, derived from renewable biomass, offer several advantages, including biodegradability, biocompatibility, and lower production costs, making them attractive candidates for eco-friendly fuel cell membranes [14,15]. Among these, gelatin, a widely available natural polymer, has emerged as a potential alternative due to its unique physiochemical properties and structural tunability [16].

Gelatin is a biodegradable and renewable biopolymer that is derived from the partial hydrolysis of collagen found in animal connective tissues and is known for its good mechanical properties [17], hydrophilicity, and film-forming capability [18]. The molecular structure of gelatin consists of polypeptide chains rich in glycine, proline, and hydroxyproline, which contribute to its high flexibility, elasticity, and water retention capability [19,20]. In addition, gelatin can also form hydrogels with adjustable porosity and swelling behavior, making it an ideal candidate for membrane applications that require controlled water uptake and ionic transport properties [21]. Its environmentally friendly origin, low carbon footprint, and biodegradability offer a sustainable alternative to synthetic PEMs like Nafion, which are based on non-renewable fluorinated polymers. The growing focus on green hydrogen technologies makes the integration of such bio-based membranes especially attractive for future clean energy systems.

Beyond fuel cell applications, gelatin-based membranes have demonstrated potential in other energy-related technologies, including flexible electronics and supercapacitors [22]. The growing demand for lightweight, flexible, and sustainable materials in next-generation electronic devices has driven researchers to explore gelatin’s multifunctional properties for energy storage and conversion applications [23,24]. Similarly, in supercapacitors, gelatin-based electrolytes have been investigated for their role in charge–discharge cycles, presenting an opportunity for developing environmentally friendly energy storage systems [25]. While gelatin has been extensively studied in medical applications, such as tissue engineering [26], wound healing [27], and drug delivery [28], its utilization in electrochemical energy systems remains relatively underexplored. Its ability to retain water and form hydrogels has been widely exploited in biomedical fields to enhance cell adhesion, drug encapsulation, and controlled release mechanisms [26]. By leveraging insights from biomedical research, gelatin-based membranes can be further tailored to meet the performance requirements of energy applications, ensuring optimal mechanical flexibility, ionic conductivity, and operational stability under electrochemical conditions. This interdisciplinary approach can provide new avenues for designing bio-derived membranes with enhanced functionalities for sustainable energy technologies.

In addition to gelatin, other natural biopolymers, such as chitosan, cellulose, and starch derivatives, have been widely studied for PEM applications. Chitosan offers intrinsic proton conductivity and film-forming ability but suffers from brittleness and limited thermal stability [29]. Cellulose-based membranes are mechanically robust but often require chemical modification to support adequate ionic transport [30]. Starch derivatives are inexpensive and biodegradable, yet their stability under humid electrochemical conditions remains a challenge [31]. In contrast, gelatin combines mechanical flexibility, high water uptake, and ease of chemical tunability, making it a unique candidate among natural polymers. This study aims to systematically investigate these advantages in the context of electrochemical energy applications. Additionally, recent studies on polypropylene-based pulsating heat stripes have emphasized the critical role of polymer flexibility and thermal behavior in emerging energy and electronics applications. For instance, Der et al. [32] demonstrated how polymer orientation, loop geometry, and heat transfer fluid properties impact the thermal regulation and dynamic response of flexible heat management systems. Similarly, they also explored how plastic-based heat stripes achieve stable thermal performance through smart material integration, even under pulsed loading conditions. These studies highlight the growing importance of thermomechanical stability and structural adaptability in flexible systems, challenges that align closely with those faced in the design of proton-conducting membranes [33]. Although our work focuses on electrochemical rather than thermal applications, the integration of gelatin with plasticizers like PEG and IL reflects a similar materials-driven strategy to enhance flexibility, resilience, and environmental performance in next-generation flexible devices.

Herein, this research aims to investigate the synthesis, characterization, and performance of gelatin-based membranes for energy applications, focusing on their potential use in low-temperature fuel cells. These membranes were developed based on gelatin in combination with PEG, glycerol, and ionic liquids (ILs). The ILs selected for this study were chosen based on their intrinsic properties that support ionic conductivity and membrane stability. Specifically, imidazolium-based ILs were incorporated because of their high ionic mobility, electrochemical stability, and compatibility with gelatin matrices [34]. These ILs facilitate enhanced proton conductivity through hydrogen bonding and ion transport pathways while also acting as plasticizers to improve membrane flexibility. Their low volatility and thermal stability also contribute to the long-term performance of the membranes under fuel cell operating conditions [35]. To the best of the authors’ knowledge, such membranes and characterization have not yet been described in the literature. A systematic experimental approach was employed to evaluate the physiochemical and electrochemical properties of these membranes, including water uptake, ionic conductivity, and mechanical behavior. By testing the incorporation of plasticizers, fillers, and other agents, this work seeks to advance the development of cost-effective, high-performance membranes for next-generation energy storage and conversion technologies.

2. Materials and Methods

2.1. Materials

The materials used in this study include gelatin (derived from bovine skin purchased from Sigma Aldrich-CAS# 9000-70-8, St. Louis, MO, USA) as the primary polymer matrix, alongside a selection of additives to modify membrane properties. Bovine-derived gelatin was selected over other sources (e.g., porcine or fish) because of its higher gel strength, thermal stability, and superior mechanical performance, which are advantageous for membrane formation. Its broader acceptance in various regulatory and cultural contexts also supports its use in green and biocompatible energy applications. The additives used in this work include glycerol, polyethylene glycol (PEG), both purchased from Sigma Aldrich), and ionic liquid Diethylmethylammonium methansulfonate ([DEMA][OMs], purchased from IoLiTec, Heilbronn, Germany, and used as received). The gelatin and the additives were all used as purchased. Deionized (DI) water and acetic acid were employed as solvents during the membrane fabrication process and used without further modification or purification.

2.2. Membrane Synthesis

The membranes were synthesized using a solution-casting method. Initially, 1 g of gelatin was dissolved in 20 mL of solvent (deionized water or acetic acid) at a controlled temperature of 50 °C with continuous stirring for 30 min to ensure homogeneity. Once fully dissolved, the additives were incorporated in the amounts specified in

Table 1. Performance results of the composite membranes.

	Composition	t (cm)	$\mathbf{R}\mathbf{in}\mathbf{\left(}\mathsf{\Omega }\mathbf{\right)}$	$\mathit{\sigma }$ (Scm−1)	Elasticity
1	1 g Gelatin	0.010	122.8	1.0368 × 10−4	Bendable and not stretchable
2	1 g Gelatin + 0.2 g glycerol	0.006	118.4	6.452 × 10−5	Bendable and stretchable
3	1 g Gelatin + 0.5 g glycerol	0.016	64.12	3.1771 × 10−4	Bendable and stretchable
4	1 g Gelatin + 0.2 g glycerol + 0.2 g IL	0.005	39.59	1.6080 × 10−4	Bendable and stretchable
5	1 g Gelatin + 0.2 g PEG	0.015	79.12	2.4139 × 10−4	Bendable and stretchable
6	1 g Gelatin + 0.5 g PEG	0.020	133.4	1.9089 × 10−4	Bendable and stretchable
7	1 g Gelatin + 0.2 g PEG + 0.2 g IL	0.015	9.524	2.0053 × 10−4	Bendable and stretchable
8	1 g Gelatin + 0. 2 g IL	0.024	73.08	4.181 × 10−4	Bendable and stretchable

(which also shows the conductivities as mentioned later in this context) to modify the mechanical and electrochemical properties. The prepared solutions were then cast onto glass substrates and subjected to a two-step drying process: first, on a hot plate at approximately 45 °C for 6 h, followed by drying at room temperature for 24 h to allow gradual solvent evaporation and membrane formation. The resulting membranes were carefully peeled off and stored in airtight polyethylene bags in a desiccator until testing to prevent moisture uptake before characterization.

2.3. Characterization Techniques

The synthesized membranes were characterized by various techniques to evaluate their physiochemical and electrochemical properties.

2.3.1. Electrochemical Impedance Spectroscopy

The proton conductivity of the fabricated membranes was assessed using electrochemical impedance spectroscopy (EIS). The membrane samples were cut and placed between two symmetrical electrodes within a specially designed stainless-steel cell. The measurement setup utilized a four-probe configuration, with the cell connected to an SP-200 Potentiostat from Biologic, Seyssinet-Pariset, Auvergne-Rhone-Alpes, France. The impedance was recorded across a frequency range of 100 Hz to 7 MHz using EC-Lab software (V11.10). The resistance (R) of the membrane was determined from the intersection of the Nyquist plot at the high-frequency region and also using EC-Lab software, which corresponds to the bulk ionic resistance of the membrane. The obtained R value was then used to calculate the proton conductivity. The proton conductivity (σ) was then calculated using Equation (1):

$$\sigma ={\displaystyle \frac{t}{R\times A}}$$

(1)

where t is the membrane thickness in cm, R is the resistance in ohms, and A is the cross-sectional area of the electrodes. All impedance measurements were performed under typical ambient laboratory conditions, with room temperature ranging between 24 and 26 °C. Although humidity was not actively controlled, the relative humidity remained stable in the range of 45–55% during the measurement period. To reduce variability, the membranes were tested within a consistent time window following preparation and stored in sealed containers prior to analysis.

2.3.2. Water Uptake Test

Water uptake was measured by weighing the membranes in their dry state and after immersing them in deionized water for 24 h. The water uptake percentage was calculated using Equation (2):

$$WU={\displaystyle \frac{W_{wet}-W_{dry}}{W_{dry}}}\times 100$$

(2)

where $W_{wet}$ and $W_{dry}$ represent the hydrated and dried membrane weights, respectively. Water uptake tests were also conducted under ambient lab conditions (24–26 °C, RH 45–55%). While humidity was not precisely regulated, the samples were weighed under consistent conditions using the same setup and workflow for all compositions.

2.3.3. X-Ray Diffraction

X-ray diffraction (XRD) was performed using a Bruker D8 diffractometer (Billerica, MA, USA) to investigate the crystalline structure and phase compositions.

2.3.4. Scanning Electron Microscopy

Scanning electron microscopy (SEM) was conducted using a Tescan VEGA XMU microscope (Brno, Czech Republic) to examine the surface morphology and analyze the molecular structure of the synthesized membranes.

2.3.5. Energy Dispersive Spectroscopy

Elemental characterization and mapping of the membranes were performed using energy dispersive spectroscopy (EDS). The measurements were conducted with a Tescan VEGA XMU SEM (Brno, Czech Republic) equipped with a LaB6 electron source and an Oxford Instruments X-Max (Abingdon, UK) 50 mm² silicon drift detector (SDD). This technique identifies and maps elemental distributions by detecting the characteristic X-rays emitted from the sample surface upon interaction with a focused electron beam.

3. Results and Discussion

3.1. Electrochemical and Mechanical Performance Results

The electrochemical performance of the fabricated membranes was evaluated in terms of their proton conductivity (σ). The results of these measurements, obtained from EIS analysis, are summarized in Table 1 and described in detail below. While full fuel cell testing was outside the scope of this study, the EIS measurements under controlled conditions provided a reliable quantification of proton conductivity. The results indicate significant variations in conductivity and mechanical behavior depending on the composition of the membranes. The pure gelatin membrane using DI water as solvent exhibited a proton conductivity of 1.0368 × 10⁻⁴ Scm⁻¹, which is relatively low due to the absence of conductivity-enhancing additives. Moreover, upon the incorporation of ionic liquid [DEMA][OMs] the conductivity significantly improved, with the gelatin/0.2 g IL membrane achieving the highest value of 4.181 × 10⁻⁴ Scm⁻¹. This enhancement is attributed to the ability of IL to create additional proton-conducting pathways by increasing membrane hydration and ionic mobility [36]. Similarly, PEG and glycerol also contributed to increased conductivity, likely due to their plasticizing effect, which enhances membrane flexibility and facilitates proton transport.

Among the tested combinations, the gelatin membranes with both glycerol and IL demonstrated synergistic effects, with improved conductivity and mechanical behavior. For example, the gelatin/0.2 g glycerol/0.2 g IL membrane achieved 1.6080 × 10⁻⁴ Scm⁻¹, indicating a favorable balance between mobility and structural integrity. The synthesized composite membranes can be observed in Figure 1. From a mechanical standpoint, most of the membranes were bendable, but only certain formulations were stretchable. The gelatin membrane was bendable but not stretchable, whereas the membranes containing IL, PEG, and glycerol exhibited both bendability and stretchability. Membrane integrity was confirmed by visual inspection, revealing uniform thickness, flexibility, and the absence of cracks or phase separation, characteristics consistent with continuous polymer membranes. While mechanical testing was not performed in this work, it will be a focus of future studies to quantify tensile strength and elongation at break. Notably, gelatin/0.5 g glycerol demonstrated an excellent balance between proton conductivity at 3.1771 × 10⁻⁴ Scm⁻¹ and mechanical flexibility, making it a promising candidate for further optimization. Overall, the data highlights the potential of combining gelatin with the selected additives to produce membranes with enhanced electrochemical performance and mechanical versatility. Although the conductivity values of the developed membranes are lower than those of benchmark commercial membranes, such as Nafion (0.1 Scm⁻¹ under fully hydrated conditions at room temperature), it is important to note that Nafion’s conductivity can significantly decrease at elevated temperatures and low humidity, often falling below 10⁻⁴ Scm⁻¹. In contrast, the membranes reported here maintain stable performance in similar conductivity ranges while offering advantages in sustainability, biodegradability, and mechanical flexibility. These attributes position them as promising alternatives for applications prioritizing eco-friendliness and structural adaptability over maximum conductivity alone. Although the gelatin/0.2 g IL membrane exhibited the highest absolute proton conductivity, the gelatin/0.2 g PEG/0.2 g IL membrane demonstrated a more favorable trade-off between conductivity, water uptake, and mechanical flexibility. These combined properties are essential for practical use in flexible electronics and PEM fuel cells, where durability and hydration stability are just as critical as conductivity.

The electrochemical and mechanical performance of the gelatin-based membranes suggests that they hold strong potential for integration into real fuel cell systems. Their combination of proton conductivity, structural flexibility, and hydration capacity is aligned with the requirements of low-temperature PEM fuel cells. While full-cell testing was beyond the scope of this study, future work will involve evaluating these membranes under operational conditions, including assessments of fuel crossover, oxidative durability, and long-term electrochemical cycling.

3.2. Water Uptake Results

Water uptake is an important property in proton exchange membranes, as it directly influences ionic conductivity and mechanical stability. High water content enhances proton conductivity by increasing the availability of hydrated domains within the membrane matrix [37]. These water-rich regions facilitate proton transfer through two primary mechanisms: the Grotthuss mechanism, which involves proton hopping across hydrogen-bonded networks, and the vehicular mechanism, where protons are transported along with water molecules. In gelatin-based membranes, the hydrophilic nature of the polymer supports water absorption, enabling efficient ionic transport, which is essential for fuel cell performance [38]. The water uptake results for the different membrane compositions indicate significant variations depending on the type and concentration of additives. For instance, the pure gelatin membrane exhibited a high-water uptake of 442.75%, which is attributed to the hydrophilic nature of gelatin and its ability to retain moisture [39]. However, adding different plasticizers and ionic liquid significantly altered the water retention properties. The highest water uptake was recorded for gelatin/0.2 g glycerol/0.2 g IL (906.55%), gelatin/0.2 g PEG/0.2 g IL (775.07%), and 1 g gelatin/0.2 g IL alone (627.27%). The common factor in these compositions is the presence of ionic liquid ([DEMA][OMs]), which enhances water retention by increasing the membrane’s hydrophilicity and promoting the formation of water-rich domains [40]. Conversely, the lowest water uptake values were observed for gelatin/0.2 g glycerol (281.27%) and 1 g gelatin/0.5 g glycerol (183.61%). This suggests that while glycerol acts as a plasticizer, it does not significantly contribute to water retention, possibly due to its limited ability to form hydrogen-bonded networks compared to IL and PEG. Similarly, the membranes containing higher amounts of PEG, such as 1 g gelatin/0.5 g PEG, demonstrated a moderate water uptake of 439.63%, indicating that PEG contributes to moisture absorption without excessive swelling.

These findings emphasize the importance of additive selection and concentration in tailoring the membrane’s hydrophilic behavior. The results indicate that the best-performing membranes in terms of both water uptake and conductivity are gelatin/0.2 g PEG/0.2 g IL and gelatin/0.2 g IL. These formulations maintain the highest proton conductivity while exhibiting optimal water retention, making them promising candidates for fuel cell applications. However, it is important to note that while the incorporation of IL, PEG, and glycerol significantly improved water uptake and proton conductivity, potential leaching of these additives under operating conditions remains a concern. Prolonged exposure to water or temperature fluctuations could lead to additive migration, potentially affecting membrane integrity and performance over time. Future work should therefore investigate leaching behavior and long-term electrochemical stability through extended durability testing and post-operational analysis. The observed correlation between high water uptake values and improved proton conductivity (Section 3.1) strongly supports the conclusion that proton transport in these membranes is facilitated by hydrated domains within the gelatin matrix. The presence of the hydrophilic ionic liquid ([DEMA][OMs]) enhances these domains, enabling proton migration primarily via the Grotthuss and vehicular mechanisms. The amorphous nature of the membranes, confirmed by XRD, and the absence of metallic phases in EDS analysis further indicate that electronic conduction is negligible, and protons are the dominant charge carriers.

3.3. X-Ray Diffraction Results

The XRD patterns presented in Figure 2 compare four gelatin-based membranes: pure gelatin, gelatin with 0.2 g PEG, gelatin with 0.2 g ionic liquid (IL), and gelatin with both 0.2 g PEG and 0.2 g IL. Although all the samples retain the characteristic broad halo typical of amorphous biopolymers, there are noticeable differences in peak intensities and subtle variations in peak position. In the pure gelatin sample, the diffraction profile displays a broad peak centered roughly around 2θ = 19–21°, which aligns with the amorphous nature of gelatin reported in the literature [41]. The low-intensity, wide hump indicates limited long-range ordering. Any minor shoulders near 2θ = 7–10° can be ascribed to local ordering or residual helical arrangements [42]. However, these features remain quite weak, reinforcing that unmodified gelatin is predominantly amorphous. Upon incorporating 0.2 g PEG into the gelatin matrix, the main broad peak becomes slightly more pronounced and may exhibit a marginal shift toward higher 2θ angles. This increased intensity suggests that PEG, through hydrogen bonding or other intermolecular interactions, induces a more organized arrangement of gelatin chains. Nonetheless, the persistence of a single broad peak implies that the sample does not develop a distinctly crystalline phase; rather, PEG appears to enhance the semi-crystalline-like domains or promote tighter packing within the otherwise amorphous network. In contrast, 0.2 g IL-modified gelatin also shows an increase in peak intensity relative to pure gelatin, but the shape of the broad peak differs subtly from the PEG-containing sample. Ionic liquids often act as plasticizers or disruptors of hydrogen-bonded networks, so this difference could be attributed to how the IL interacts with the polypeptide chains [43]. The IL may facilitate partial alignment of the chains without creating well-defined crystalline domains. The result is a broad peak that remains characteristic of an amorphous structure but with a slight enhancement in ordering. The most pronounced effect is observed when PEG and IL are both present in the gelatin matrix. The XRD pattern in this case exhibits a more intense broad peak than either single-additive sample, implying synergistic effects between PEG and IL on the structural arrangement of the gelatin chains. Although no sharp diffraction peaks emerge, confirming the absence of a new crystalline phase, this heightened intensity can be interpreted as a further increase in the semi-ordered regions. It is possible that PEG and IL collectively promote more extensive chain interactions, leading to denser packing or partial alignment of the gelatin network.

3.4. Scanning Electron Microscopy Results

Figure 3 shows the SEM images of the pure gelatin membrane at magnifications of 10,000×, 30,000×, and 60,000×. The surface appears relatively smooth and compact at lower magnification, suggesting a homogeneous film without significant phase separation or porosity. Closer inspection at higher magnifications reveals subtle roughness and minor irregularities that are typical of protein-based matrices once dried, reflecting the inherent brittleness and moderate shrinkage of pure gelatin films.

On the other hand, Figure 4 presents the SEM micrographs of the gelatin/0.2 g IL membrane at 10,000×, 30,000×, and 60,000×. Compared to pure gelatin, the surface morphology here is slightly more uniform, which can be attributed to the plasticizing or disruptive effect of the ionic liquid on the gelatin network. The ionic liquid may facilitate partial chain mobility and reorganization, leading to a smoother appearance; however, localized variations or faint aggregate-like features may also be observed, indicating that IL distribution within the matrix is not perfectly homogeneous at all scales.

Figure 5 displays the SEM images of the gelatin/0.2 g PEG membrane at 10,000×, 30,000×, and 60,000×. The introduction of PEG tends to result in an even smoother film surface, as PEG can promote better film formation and reduce brittleness through hydrogen bonding with the gelatin chains. Any micro-voids or pores appear smaller and more dispersed, suggesting good compatibility between PEG and gelatin. This more uniform surface is often associated with enhanced mechanical flexibility and reduced surface defects.

Similarly, Figure 6 shows the SEM images of the gelatin/0.2 g PEG/0.2 g IL membrane at 10,000×, 30,000×, and 60,000×. Here, the combination of PEG and IL seems to have a synergistic effect, producing a highly uniform and flattened surface at lower magnifications. Although minor topographical variations or shallow indentations can still be detected at the highest magnifications, the overall morphology is indicative of enhanced polymer chain interactions and improved film integrity.

3.5. Energy Dispersive Spectroscopy Results

The EDS results shown in Figure 7 represent the four gelatin-based membranes, which show variations in elemental composition depending on the presence of the IL and PEG. The pure gelatin membrane exhibits a high carbon (C) content of 71.1 wt% and an oxygen (O) content of 27.5 wt.%, with a small amount of 2.4 wt.% chlorine (Cl), which is likely from residual processing agents. Furthermore, the addition of the IL slightly increases the carbon content up to 72.8 wt.% while reducing oxygen to 21.4 wt.% and introducing sulfur (S), at an amount of 4.7 wt.%, indicating the presence of IL components. Similarly, the gelatin/PEG membrane maintains a similar carbon and oxygen distribution (72.4 wt.% C and 24.3 wt.% O), with minor traces of copper (Cu) (0.4 wt.%), which may originate from sample preparation. The combination of PEG and the IL reduces the carbon content slightly to 69.9 wt.% while increasing oxygen up to 26.6 wt.%, as well as sulfur to 4.1 wt.%, confirming the integration of both additives. The Au peaks observed in the sample are due to the samples’ coating prior to SEM. The minor Cu peaks detected are perhaps due to the overlap with other elemental signals. The variations in the sulfur and oxygen contents highlight the influence of the IL in modifying the membrane composition, while PEG contributes to maintaining a balanced carbon–oxygen ratio.

4. Conclusions

In this study, gelatin-based membranes were successfully synthesized and modified with various additives, including ILs, PEG, and glycerol, to evaluate their electrochemical, mechanical, and water uptake properties. The results demonstrated that the addition of the IL significantly enhanced proton conductivity, with the highest recorded value of 4.181 × 10⁻⁴ Scm⁻¹ for the gelatin/0.2 g IL membrane. This improvement is attributed to the IL’s ability to promote hydration and create additional proton-conducting pathways. Additionally, PEG and glycerol contributed to improved flexibility and conductivity, with the gelatin/0.5 g glycerol membrane showing a favorable balance between mechanical performance and conductivity. Water uptake analysis revealed that the IL-containing membranes, particularly gelatin/0.2 g PEG/0.2 g IL and gelatin/0.2 g IL, exhibited the highest hydration levels, further supporting their role in enhancing conductivity. SEM and EDS characterization confirmed the structural and elemental modifications due to additive incorporation. Despite these promising results, some challenges remain. The proton conductivities achieved, while improved, remain lower than those of Nafion under fully hydrated conditions (0.1 Scm⁻¹). Moreover, potential leaching of ILs and plasticizers under long-term operating conditions could impact durability and performance. There is also a need for further testing under elevated temperatures and reduced humidity conditions to simulate real-world PEM fuel cell environments. Addressing these challenges through further material optimization and long-term stability assessments will be essential for translating these findings into practical, commercial-scale applications. In addition to leaching, the long-term thermal and electrochemical stability of gelatin must be assessed, as biopolymers can be prone to oxidation or hydrolytic degradation under sustained operation. Future work will involve aging studies and in-operation testing to evaluate membrane durability under realistic PEM fuel cell conditions. Nonetheless, this study demonstrates that bio-based gelatin membranes modified with IL and PEG offer a viable pathway toward eco-friendly, flexible, and moderately conductive alternatives for next-generation fuel cell membranes and flexible electronics.