Composite Proton Exchange Membranes Research Articles

Amination modification of graphene oxide for the in-situ synthesis of sulfonated polyimide-based composite proton exchange membranes

To mitigate the severe degradation of mechanical properties and stability of highly sulfonated proton exchange membranes (PEMs) caused by the sulfonic acid groups, amino-functionalized graphene oxide (AGO) was embedded into sulfonated polyimide (SPI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of AGO nanoparticles facilitated the enhancement of the crystallinity of the composite membrane, with the well-constructed interface and dispersion. The resulting AGO-SPI composite membrane exhibited high mechanical strength and stability. The fracture strength of AGO-SPI composite membrane was approximately 61 MPa, which was 1.85 times higher than that of pure SPI. Meanwhile, the weight loss of AGO-SPI composite membrane in Fenton’s reagent was only 2.11 %. Additionally, at 90 °C/98 % RH, the proton conductivity of AGO-SPI composite membrane reached 50.1 mS cm−1, which was 3.53 times higher than that of pristine SPI. The results suggest the promising application prospects of the proton exchange composite membrane.

Advanced Nafion/nanofiller composite proton exchange membranes for fuel cell applications

Proton exchange membrane fuel cells (PEMFCs) exhibit increasing potential in a variety of applications, from automotive to stationary power generation, due to their superior advantages such as high efficiency, quick start-up and low emissions. The cell performance and operation life of PEMFCs are directly affected by the proton exchange membranes (PEMs). Nafion, a well-known perfluorosulfonic acid polymer, represents the state of the art of PEMs. To further improve the performance of Nafion, various nanofillers are incorporated into Nafion matrices, leading to the formation of composite PEMs with enhanced proton conductivity, mechanical strength and chemical stability. This review summarizes the recent advancements in Nafion composite PEMs based on four typical kinds of nanofillers: framework nanomaterials, carbon nanomaterials, polyoxometalate nanoclusters, and inorganic oxide nanoparticles. The preparation strategy, structure-property relationship and fuel cell applications of these membranes are discussed comprehensively, particularly focusing on the synergistic effect between Nafion and nanofillers. This review can provide an instructive insight for designing high-performance PEMs towards emerging energy technologies.

Testing of Polymer Film–Sulfonated Polystyrene Proton-Exchange Composite Membranes in a Direct Methanol Fuel Cell at 60°C. Methanol Crossover

Testing of Polymer Film–Sulfonated Polystyrene Proton-Exchange Composite Membranes in a Direct Methanol Fuel Cell at 60°C. Methanol Crossover

Supramolecular complexation of metal oxide clusters in PVDF-PVP blends for large scale fabrication of proton exchange membranes for fuel cells

The perfluorosulfonic acid (PFSA) polymers have achieved great success as proton exchange membranes (PEMs) in various energy storage and conversion devices; nevertheless, the improvements regarding PEMs' synthetic cost, mechanical properties, stability and processability are still urgently required. Herein, 1 nm super acidic metal oxide cluster, H3PW12O40 (PW12), is complexed with the blends of polyvinylpyrrolidone (PVP) and polyvinylidene fluoride (PVDF) to afford nanocomposite PEMs that enables the stable and effective operation of hydrogen fuel cell devices. As the polymer matrix, the PVDF is blended with PVP via inter-chain hydrogen bonding to provide mechanical support for the nanocomposite PEMs. The further introduced PW12 clusters can interact strongly with PVP via electrostatic attraction to enhance the PEMs' mechanical strength (E = 231 MPa) and prevent the leaching of PW12 for long-term stability. Meanwhile, the incorporation of the super acidic PW12 can facilitate the fast proton transportation and therefore, lead to the significant increasement of proton conductivity to 9.8 × 10−3 S cm−1 at 70 °C and 100% RH. Due to the excellent mechanical properties and the supramolecular interaction among the components, the PEMs’ thickness can be controlled to be challenging ∼10μm for feasible large-scale continuous processing. Finally, the molecular design enables the successful fabrication of the nanocomposite PEMs into fuel cell devices with the power density as 342.8 mW cm−2. The studies not only shed light on the structure-properties of polymer nanocomposites, but also pave avenues to the design of robust composite PEMs for fuel cell appliacations.

Polynorepinephrine-regulated filler sulfonation toward interfacial reformation and conductive promotion of nanocomposite proton exchange membrane

Interfacial compatibility between filler and matrix substantially affects the overall morphology and performance of nanocomposites. Compared with bare montmorillonite (MMT), surface modified product such as sulfonated MMT (SMMT) has been known to render optimized interfacial compatibility in composite proton exchange membranes (PEMs) for proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Nevertheless, in-depth understanding and investigation on the sulfonation of MMT are seldom focused, such as uniformity and sufficiency. Herein, these broadly neglected issues are proposed and resolved using an exemplary polynorepinephrine (PNE)-regulated SMMT (SNMMT). Rather than direct sulfonation utilizing the inherent hydroxyl groups of MMT, a PNE coating with ample hydroxyl groups is deposited on MMT beforehand, which results in more homogeneous and sufficient sulfonation of SNMMT. Compared with normal SMMT, this alteration on surficial geography of filler functionalization brings significant benefits when composited with Nafion matrix, including harmonized filler-matrix compatibility, improved mechanical stability and enhanced proton conduction. Moreover, the antioxidative ability of PNE layer enables improved chemical stability of nanocomposite PEM. The Nafion/SNMMT composite PEM achieves 0.275 S cm−1 proton conductivity at 95 °C in water, evidently beyond any previously reported composite PEMs using normal SMMT. Equipped with this reformed nanocomposite PEM, both PEMFC and DMFC display competitive peak power densities (1.121 W cm−2 with H2/O2 at 80 °C/100 % relative humidity (RH) for PEMFC, and 0.228 W cm−2 with 1.6 M methanol/100 % RH O2 for DMFC), and simultaneously show minor performance deteriorations in constant current density operation and RH cycle tests. It would be instructive the specific focus and reformation on the uniformity and sufficiency of filler modification may render significant interface and performance advancements for nanocomposites.

Sulfonation modification of halloysite nanotubes for the in-situ synthesis of polybenzimidazole-based composite proton exchange membranes in wide-temperature range applications

Phosphoric acid-doped polybenzimidazole (PA–PBI) membranes face challenges, such as the easy loss of free PA and the reduced mechanical strength caused by the “plasticization effect” of PA, limiting their application in a wide temperature range. In this study, sulfonated halloysite (sHNT) was used to modify poly(2,5-benzimidazole) (ABPBI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of halloysites in the composite membrane enabled the capturing of PA and water, while its nanoporous structure provided additional paths for proton conduction. Sulfonation modification of halloysite improved the interfacial compatibility between the inorganic particles and the polymer matrix, with the –SO3H groups providing extra proton hopping sites. Due to the well-constructed interface, the resulting sHNT/ABPBI composite membrane exhibited high mechanical strength and excellent proton conductivity across a wide temperature range. The 3 % sHNT/ABPBI composite membrane exhibited a breaking strength of approximately 130 MPa, which was 1.6 times that of pure ABPBI. Moreover, the proton conductivity of the composite exceeded 0.01 S cm−1 at temperatures ranging from 40 to 180 °C. At 160 °C, the peak power density of the PA-doped 3 % sHNT/ABPBI composite membrane was 0.212 W cm−2, which was 1.33 times higher than that of the pure ABPBI membrane. These results show that the composite membrane has potential applications in a wide temperature range.

Improving MFC efficiency in power generation and COD removal by using protic ionic liquid in MWCNT-CS-2-aminothiazole-SO3H nanoparticle-infused sulfonated PES

This study exhibits a novel nanofiller, functionalized multi-walled carbon nanotube (MWCNT)/chitosan (CS) by 2-aminothiazole/SO3H. This synthesized nanofiller was incorporated with a fabricated sulfonated polyethersulfone (SPES) to manufacture a composite proton exchange membrane (PEM), SPES/MWCNT-CS-2-aminothiazole-SO3H. The composite membranes were fabricated by different percentage amounts of nanofiller (0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%). The trait comparison of SPES/MWCNT-CS-2-aminothiazole-SO3H, SPES, and Nafion 117 membrane is performed to investigate their application in the microbial fuel cell (MFC). The fabricated composite membrane SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt% illustrated superior water uptake (WU) of 90.41 %. Moreover, the maximum power density (PD) (66.04 mW.m−2) was produced by SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt%, which demonstrated a considerable increase (approximately 20 times) compared to SPES (3.19 mW.m−2). Furthermore, the power density generated by the Nafion 117 membrane was 15.78 mW.m−2. In addition, the statistics in MFC usage presented that prepared composite membrane combined with MWCNT-CS-2-aminothiazole-SO3H 0.5 wt% had the optimum chemical oxygen demand (COD) removal, and the coulombic efficiency (CE), with 90.46 % and 80.68 %, respectively. Due to the high efficiency and remarkable power generation achieved by the MFC with SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt%, this modified membrane can be considered as a promising cost-effective alternative separator in MFC.

Adjusting structure-activity relationship to obtain hybrid proton exchange membrane with enhanced transport efficiency by introducing functionalized nano-coated MOFs

Designing proton exchange membranes (PEMs) with high H+ conductivity and good dimensional stability has been a challenge. The porous structure of ZIF-8 could load ionic liquids (IL) (ZIF-8@IL). The ZIF-8@IL was coated by sulfonated polydopamine (SPDA), then ZIF-8@IL-SPDA as proton conductors was fabricated. ZIF-8@IL-SPDA would not lose in water environment like small molecule proton conductors (such as sulfuric acid, phosphoric acid, imidazole, etc.). The different loadings of ZIF-8@IL-SPDA were introduced into sulfonated poly (aryl ether ketone sulfone) containing fluorene groups (F-SPAEKS). The novel composite PEMs was investigated. The prepared hybrid matrix membrane with optimum ZIF-8@IL-SPDA doping content (1.5 wt%) showed the highest H+ conductivity of 149.87 mS cm−1 at 80 °C. In addition, a maximum peak power density of 818 mW cm−2 was achieved in a single-cell performance test of this membrane. The good dispersion of ZIF-8@IL-SPDA nanoparticles in the F-SPAEKS matrix reduced the fuel cross-over flux to 2.15 mA cm−2. Therefore, the newly prepared hybrid matrix membranes were expected to be applied in proton exchange membrane fuel cells.

Poly(arylene ether ketone sulfone)s functionalized with adenosine triphosphate-modified graphene oxide as proton exchange membranes for fuel cells

In this study, composite proton exchange membranes (PEMs) based on functional graphene oxide (GO) and carboxyl-containing sulfonated poly(arylene ether ketone sulfone)s organic matrix (C-SPAEKS) were synthesized. Modified GO nanosheets (ATP@GO) was synthesized by using GO as a template, then chemically bonded adenosine triphosphate (ATP) on GO nanosheets. Modified ATP@GO and composite membranes were characterized by FT-IR, 1H NMR, SEM and XPS. These composite membranes exhibit outstanding proton conductivity, thermal stability and dimensional stability. Compared to C-SPAEKS membranes (32.3 mS cm−1 at 20 °C, 108.9 mS cm−1 at 90 °C), C-SPAEKS/ATP@GO-1 membrane showed enhanced proton conductivity (50.0 mS cm−1 at 20 °C, 184.8 mS cm−1 at 90 °C). Meanwhile, the open circuit voltage (OCV) and power density of C-SPAEKS/ATP@GO-1 were 0.9941 V and 466.33 mW/cm2, respectively, which were much higher than the C-SPAEKS (0.8973 V, 190.72 mW/cm2), showing good fuel cell performance. The results show that functionalized GO could make an important contribution to proton conduction and improvement of comprehensive performance in composite membrane, which indicate that these composite membranes have the potential to be used as PEMs.

Achieving better balance on the mechanical stability and conduction performance of sulfonated poly(ether ether ketone) proton exchange membranes through polydopamine/polyethyleneimine co-modified poly(vinylidene fluoride) nanofiber as support

In this work, the polyvinylidene fluoride (PVDF) electrospun fibers was applied as robust mechanical support and subsequently functionalized with polydopamine/polyethyleneimine (PDA/PEI) composite, then filled with sulfonated poly (ether ether ketone) (SPEEK) to obtain SPEEK-PDA/PEI@PVDF composite proton exchange membranes. The composite membranes achieved better balance on the mechanical stability and conduction performance, owing to enhanced interface interactions and compatibility between robust PVDF and conductive SPEEK. In wet conditions, the composite membrane exhibited excellent mechanically robust with tensile strength of 34 MPa and elongation at break of almost 200 %. Furthermore, the composite membranes also showed high structure and performance stability during the measurement of proton conductivity and fuel cell performances, it could hold stable proton conductivity of 48 mScm−1 (at 80 °C) and maximum power density of 58.9 mWcm−2. The durability test further confirmed the super operating stability of composite membrane, only 2.6 % reduction in open circuit voltage was observed during operated at 80 °C for 100 h.

Composite proton exchange membrane for fuel cells based on chitosan modified by acid-base amphoteric nanoparticles

Currently, achieving a simultaneous improvement in proton conductivity and mechanical properties is a key challenge in using chitosan (CS) as a proton exchange membrane (PEM) substrate in direct methanol fuel cells (DMFCs). Herein, a novel nanofiller–zwitterionic molecule, (3-(3-aminopropyl) dimethylammonio) propane-1-sulfonate, ADPS)-modified polydopamine (PDA) (PDA-ADPS) was synthesized by the Michael addition reaction and was incorporated into a CS matrix to prepare CS/PDA-ADPS composite membranes. PDA-ADPS, which contains an acid–based ion pair can create new proton conduction channels in the composite membrane, improving proton conductivity. The proton conductivity of the CS/PDA-ADPS composite membrane was as high as 38.4 mS cm−1 at 80 °C. Moreover, due to the excellent compatibility and dispersibility of PDA-ADPS in the CS matrix, the obtained CS/PDA-ADPS composite membranes exhibited favorable mechanical properties. Such outstanding proton conductivity and mechanical properties guarantee good performance of the composite membranes in fuel cells. The peak power density of the CS/PDA-ADPS composite membranes was 30.2 mW cm−2 at 70 °C. This work provides a new strategy for fabricating high-performance CS based PEMs for DMFCs.

Metal-organic framework-decorated PTFE reinforced membranes with immobilized caffeic acid radical scavenger towards improved performance and durability of PEMFC

During the continuous operation of fuel cell, the generated free radicals have an irreversible effect on the proton exchange membrane (PEM), and the introduction of free radical scavengers is an effective strategy for improving its durability. In this study, we proposed to prepare thin and highly durable reinforced membranes by immobilizing organic radical scavenger caffeic acid on the fibrous PTFE supporting layer decorated with amino-functionalized metal-organic framework. The electrostatic force between the amino and sulphonic acid groups can induce an orderly aggregation of hydrophilic cationic groups within the Nafion, endowing the reinforced composite PEMs with superior proton conductivity. The mechanical properties and dimensional stability of the reinforced membranes were effectively enhanced by the reinforcement of the PTFE layer decorated with the MOF network, and the hydrogen crossover was mitigated. The thickness of Nafion reinforced membranes was reduced to 25 µm with the PTFE reinforcement. After assembling in a single cell, the Nafion composite membrane (PPUC-Nafion-3) with a 3 wt% doping of caffeic acid achieved a maximum power density (PDmax) of 812.64 mW cm−2 and the open circuit voltage (OCV) decay rate of only 1.11 mV h−1 over 100 h. For comparison under the same conditions, recast Nafion possessed a much lower PDmax of only 486.30 mW cm−2 and a higher OCV decay rate of 1.91 mV h−1. This study demonstrates an effective approach to developing highly durable and thin PEMs for the realization of PEMFC with improved output performance and durability simultaneously.

Durability improvement of proton exchange membrane fuel cells by doping silica‒ferrocyanide antioxidant

Proton exchange membranes (PEMs) with remarkable chemical stability are desirable to realize long lifetimes of proton exchange membrane fuel cells (PEMFCs). In our recent work, PEMs containing radical scavenger ferrocyanide (Fc (II))/ferricyanide (Fc (III)) species were demonstrated to possess outstanding chemical stability. However, a challenge in balancing general applicability and retention remains, due to their water solubility. Here, Fc (II) is tethered to a SiO2 support to produce low water soluble SiO2-Fc (II), which could be used as a universal additive in various matrices to mitigate leaching. The composite PEMs, sulfonated polysulfone (SPSf) doped with SiO2-Fc, show much higher oxidative stability, confirmed by Fenton's test, ion exchange capacity retention and proton conductivity retention. The composite PEM also displays obviously improved durability during PEMFC operation, where the antioxidative efficacy of SiO2-Fc is evidently stronger than comparative stand-alone water-soluble species. Moreover, a PEMFC based on SPSf composite PEM shows much higher power output than that based on unfilled SPSf membrane under low humidity conditions, owing to the hydrophilicity and proton conductivity of SiO2-Fc. The present work outlines a prospective route to better utilize Fc (II)/Fc (III) antioxidant with clear benefits in general applicability and good stability, leading to progress in utilization.

An enhanced proton conductivity of proton exchange membranes by constructing proton-conducting nanopores using PVP-UiO-66-NH-SO3H nanoparticles

The performance of proton exchange membranes (PEMs) can be enhanced by creating continuous proton conduction channels. In this work, PVP-UiO-66-NH-SO3H nanoparticles (PUNSNPs) were prepared and filled into sulfonated poly (ether ether ketone) (SPEEK) to fabricate PUNSNPs/SPEEK composite PEMs. To further improve the performance of the PEMs, phosphoric acid (PA) was doped and a continuous nanopore network was formed in PA/PUNSNPs/SPEEK porous PEMs due to the dissolution of PUNSNPs. The PA/PUNSNPs/SPEEK porous PEMs have high PA uptake ratio (96%–117 %) and dimensional stability thanks to the anchoring effect of the nitrogen-containing heterocyclic ring on the PVP chains. The acid-base pairing interaction between the chains (residual ligands from PUNSNPs) inside the unique continuous nanopore structure allows PA/PUNSNPs/SPEEK = 20 % porous PEMs to have the highest proton conductivity of 0.350 S cm−1 (80 °C/100 % RH). Furthermore, the PA/PUNSNPs/SPEEK porous PEMs retained PA up to more than 80 % (80 °C, 40 % RH, 7 days). Similarly, PA/PUNSNPs/SPEEK = 20 % porous PEMs immersed in deionized water for 45 days were able to maintain a proton conductivity of more than 83 %. Finally, PA/PUNSNPs/SPEEK porous PEMs have low methanol permeability. Thus, this study provides a new method for the preparation of porous PEMs with a continuous nanopore network structure and excellent performance.

Proton exchange membranes for polymer electrolyte fuel cells: An analysis of perfluorosulfonic acid and aromatic hydrocarbon ionomers

The design of proton-exchange membranes (PEMs) for high-performance, durable fuel cells and related electrochemical devices requires a delicate balance between high ion-exchange capacity and proton conductivity, while ensuring robust mechanical properties and preserving dimensional, chemical and thermal stability. In addition, low species crossover is desirable to reduce hydrogen peroxide formation. Ionomers used in PEMs can be classified into two main groups: (i) perfluorosulfonic acid (PFSA) polymers, and (ii) aromatic hydrocarbon (HC) polymers. In this work, an analysis of key characteristics of both PEM types is presented, including water uptake, proton conductivity, water transport properties, thermal conductivity, permeability, mechanical properties and chemical and thermal stability, among others. Comparatively, PFSA-based PEMs are undoubtedly the commercial standard due to its proven high proton conductivity and good chemical stability, even though PTFE-reinforced aromatic HC-based PEMs have also started to be commercialized recently. In the last decades, a growing trend is identified toward the development of hybrid and composite ultra-thin PEMs (5–20 μm in thickness) with tailored properties, e.g., incorporating microporous fillers to enhance water uptake and layered reinforced microstructures to improve mechanical properties and chemical stability. PEM design is to be accomplished in an environmentally friendly circular economy with facilitated recycling and re-utilization.

Design, transport efficiency and structure-activity relationship of sulfonated poly (aryl ether ketone) proton exchange membrane based on multi-functional MOFs

In this paper, two kinds of metal-organic frameworks (MOFs) with proton conduction capability were successfully prepared and added into sulfonated poly (ether ketone sulfone) (C-SPAEKS) by organic-inorganic blending. Then two different series of proton exchange membranes (PEMs) were fabricated. The template used in MOFs was UiO-66-NH2 (UN), by introducing sulfonic acid groups and imidazole groups on the template, additional proton sources and proton transport sites were constructed. Such multifunctional MOFs contributed greatly to the proton transport efficiency and structure-activity relationship of C-SPAEKS. The sulfonic acid functionalized MOFs (USN), sulfonic-acid-imidazole bifunctional MOFs (IUSN) and composite PEMs were characterized by XRD, XPS, FT-IR, 1H NMR and SEM. The prepared PEMs all have excellent proton conductivity, in which the proton conductivity of C-SPAEKS/IUSN-3% could reach 0.234 S cm−1 (80 °C and 100% relative humidity). Nafion117 had a conductivity of 0.105 S cm−1 (80 °C and 100% relative humidity), so C-SPAEKS/IUSN-3% exhibited a great enhancement on proton conductivity. Moreover, the oxidation stability of C-SPAEKS/IUSN-3% membrane was 96.97%, which was 39.32% higher than that of C-SPAEKS. These results all indicated that the as-prepared MOFs have made great contribution to improving the comprehensive properties of the sulfonated poly (aryl ether ketone) proton exchange membrane.

Development of Sulfonated Poly(vinyl alcohol)/MoS2-Based Robust Composite Proton Exchange Membranes with Higher Selectivity

Development of Sulfonated Poly(vinyl alcohol)/MoS₂-Based Robust Composite Proton Exchange Membranes with Higher Selectivity

Investigating the Sulfonated Chitosan/Polyvinylidene Fluoride-Based Proton Exchange Membrane with fSiO2 as Filler in Microbial Fuel Cells.

Chitosan (CS), a promising potential biopolymer with exquisite biocompatibility, economic viability, hydrophilicity, and chemical modifications, has drawn interest as an alternative material for proton exchange membrane (PEM) fabrication. However, CS in its original form exhibited low proton conductivity and mechanical stability, restricting its usage in PEM development. In this work, chitosan was functionalized (sulfonic acid (-SO3H) groups)) to enhance proton conductivity. The sulfonated chitosan (sCS) was blended with polyvinylidene fluoride (PVDF) polymer, along with the incorporation of functionalized SiO2 (-OH groups), for fabricating chitosan-based composite proton exchange membranes to enhance microbial fuel cell (MFC) performances. The results show that adding functionalized inorganic fillers (fSiO2) into the membrane enhances the mechanical, thermal, and anti-biofouling behavior. From the results, the PVDF/sCS/fSiO2 composite membrane exhibited enhanced proton conductivity 1.0644 × 10-2 S cm-1 at room temperature and increased IEC and mechanical and chemical stability. Furthermore, this study presents a revolutionary way to generate environmentally friendly natural polymer-based membrane materials for developing PEM candidates for enhanced MFC performances in generating bioelectricity and wastewater treatment.

Neutron scattering to probe nanostructure–property relationships in composite proton-exchange membranes for fuel cells

Neutron scattering to probe nanostructure–property relationships in composite proton-exchange membranes for fuel cells

Construction of proton transport channels in cross-linked composite membrane with highly sulfonated SPEEK nanofibers

A series of novel nanofiber composite proton exchange membranes were fabricated by embedding highly sulfonated poly (ether ketone) (SPEEK) nanofibers in a cross-linked SPEEK matrix, showing both high proton conductivity and excellent stability. Composite membranes were prepared with salt-form SPEEK nanofiber mats filled with acid-form SPEEK solution. After thermal treatment at 180 °C in the presence of dimethyl sulfoxide, the cross-linking reaction occurred in the acid-form SPEEK matrix but not in nanofibers. The dimensional stability, mechanical strength, and oxidative stability of the composite membrane were significantly improved due to thermal cross-linking treatment. The swelling ratio of all the cross-linked membranes was below 30% in hot water, and the maximum tensile strength reached 68 MPa. The nanofibers formed non-cross-linked regions and retained rich sulfonic acid groups to construct fast, long-range proton transport channels. The proton conductivity of the nanofiber composite cross-linked membrane reached 200 mS/cm exceeding the pristine cross-linked membrane (135 mS/cm). The fuel cell performance showed a peak power density of 485 mW/cm2 at 80 °C under 100% relative humidity.