Fuel cells are among the promising sources of clean energy, considering the low costs, low acoustical pollution, and the high-energy conversion. The remarkable features of graphene and its derivatives have triggered research studies on their applications in PEMFCs. PEMFCs still face some operational challenges for large-scale applications, including high costs, low proton conductivities at high temperatures, mechanical/thermal stabilities, and high fuel crossover. The unique characteristics of graphene-based materials, i.e., high electrochemical stability, good mechanical strength, large surface area, and excellent thermal stability, have been exploited in PEMFCs. This review discusses the potential role of graphene and graphene oxide (GO) in the membranes’ structural modifications, and utilization of polymer matrices such as SPEEK, PBI, PANI, SPAES, Nafion, and PVA polymers. The synthesis/functionalization of GO has been investigated with novel composite membranes and mechanisms involved in the enhancements of proton conductions, water uptakes, IECs, and power densities. Graphene materials showed excellent dispersion in solvents and alteration of membrane morphologies. The preceding properties are attributed to the formation of oxygen-based functional groups in GO nano-layers. The incorporation of graphene in other fuel cells, i.e., direct methanol fuel cells and biofuel cells, has exhibited commendable performance and appeared promising for commercial applications, especially with the reduction of fuel crossover. 

Recent developments in graphene and graphene oxide materials for polymer electrolyte membrane fuel cells applications

State-of-the-art automotive fuel cells that operate at about 80 °C require large radiators and air intakes to avoid overheating. High-temperature fuel cells that operate above 100 °C under anhydrous conditions provide an ideal solution for heat rejection in heavy-duty vehicle applications. Here we report protonated phosphonic acid electrodes that remarkably improve the performance of high-temperature polymer electrolyte membrane fuel cells. The protonated phosphonic acids comprise tetrafluorostyrene-phosphonic acid and perfluorosulfonic acid polymers, where a perfluorosulfonic acid proton is transferred to the phosphonic acid to enhance the anhydrous proton conduction of fuel cell electrodes. By using this material in fuel cell electrodes, we obtained a fuel cell exhibiting a rated power density of 780 mW cm–2 at 160 °C, with minimal degradation during 2,500 h of operation and 700 thermal cycles from 40 to 160 °C under load. High-temperature polymer electrolyte membrane fuel cells are promising for heavy-duty vehicle applications, but strides in performance are needed to improve their commercial viability. Here it is demonstrated that protonating phosphonic acid electrodes greatly enhances power density and durability. 

Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells

Optimization of catalyst layer thickness for achieving high performance and low cost of high temperature proton exchange membrane fuel cell

2D-Heterostructure assisted activation of MoS2 basal plane for enhanced photoelectrochemical hydrogen evolution reaction

Solvothermal Etching-Assisted Phase and Morphology Tailoring in Highly Porous CuFe2O4 Nanoflake Photocathodes for Solar Water Splitting

Enhanced power generation, faster transient response and longer durability of HT-PEMFC using composite polybenzimidazole electrolyte membrane with optimum rGO loading

The design of efficient heterojunction photoanodes with appropriate band alignment and ease of charge separation has been one of the most highly focused research areas in photoelectrodes. This work demonstrates the fabrication of a photoanode comprised of CdS sensitized CoFe2O4@Fe2O3 hierarchical nanosphere arrays on a FTO glass substrate and its application in photoelectrochemical water splitting. The hierarchical hematite nanosphere arrays were grown on FTO substrates by a solvothermal approach. Impregnation of Co2+ was achieved by surfactant-assisted low-temperature solvothermal phase transformation and a dipping process followed by annealing to form a CoFe2O4@Fe2O3 heterojunction. The effect of pre-annealing of substrates before the second hydrothermal step on Co2+ impregnation was studied along with the choice of the solvent. The fabricated electrodes were further sensitized with CdS nanoplate-like structures by a hydrothermal method to form a Z-scheme-Type II ternary heterojunction. The photoelectrochemical properties of the electrodes were analysed by potential linear sweep voltammetry under simulated solar irradiation (AM 1.5G, 100 mW cm−2) with a 0.5 M Na2S and 0.5 M Na2SO3 electrolyte. The highest ABPE% observed at 0.59 V (vs Ag/AgCl) was 0.86% for the photoanode comprised of CdS sensitized porous nanosphere arrays formed by solvothermal Co2+ impregnation along with pre-annealing. The fabricated electrodes showed low sheet and charge transfer resistance as observed from the EIS plot. The nanostructure morphology, crystal structure, and phase analysis were carried out using XRD, TEM, SEM and FESEM with EDAX. DFT calculations were carried out to unravel the underlying electronic structure and electron transport processes at the heterostructure interfaces. We hope to inspire more research on ordered heterostructures with superior charge transport properties, proper band alignment, enhanced light absorbance, and charge separation with this work. We also aim to focus on the effect of pre-annealing and solvent–surfactant pair selection on ion impregnation induced phase transformation in nanostructures.

Solvothermal phase change induced morphology transformation in CdS/CoFe2O4@Fe2O3 hierarchical nanosphere arrays as ternary heterojunction photoanodes for solar water splitting

Arundhati Sarkar

Papers

Enhanced power generation, faster transient response and longer durability of HT-PEMFC using composite polybenzimidazole electrolyte membrane with optimum rGO loading

Solvothermal phase change induced morphology transformation in CdS/CoFe2O4@Fe2O3 hierarchical nanosphere arrays as ternary heterojunction photoanodes for solar water splitting