Polymer electrolyte membrane fuel cells (PEMFCs) are a fast growing next-generation energy conversion technology, which hold promising interest for transportation and other applications. Nevertheless, successful commercialization of PEMFCs has been significantly retarded principally due to the high cost and poor durability of Pt/C catalysts used for anodic and cathodic reactions. Under typical fuel cell operating conditions, a traditional Pt/C catalyst is prone to degrade by various mechanisms, such as electrochemical carbon corrosion, which results in detrimental effects on the long-term performance. There have been tremendous efforts undertaken to develop durable carbon supports by introducing graphitic carbon components. In this context, carbon nanofiber supported catalysts have been investigated as highly durable supports for Pt and non-Pt nanoparticles in recent years. We anticipate it is timely to review the developments in this topic. This Review highlights the current progress on the graphitic nanofibers as a catalyst support in terms of morphology, electrocatalytic activity, various functionalization strategies, and so on, specifically focusing on the effect of nanofiber edge carbons and the advantages of surface reconstruction of nanofiber edge carbon into loops with regard to the stability of carbon support and fuel cell performance. We believe this Review stands as a guide for future researchers to figure out a rational design of oxygen reduction reaction catalysts, especially dealing with highly graphitized carbons.

The development of active, inexpensive, and durable nonprecious-metal electrocatalysts to replace high-cost Pt-based catalysts towards the commercialization of fuel cell technology is the focus in recent years. In this regard, we report a facile one-pot hydrothermal synthesis of self-assembled manganese sulfide on graphene layers (MnS/G), and is recognized as a nonprecious-metal catalyst for the efficient oxygen reduction reaction (ORR) in an alkaline medium. The phase purity and surface morphologies are investigated by using X-ray diffraction and scanning electron microscopic techniques, respectively. Optimized MnS/G with 50 % Mn exhibited excellent ORR properties with onset and half-wave potentials of 0.83 and 0.71 V vs. RHE, respectively. While evaluating the durability, only a 90 mV negative shift in its half-wave potential is observed after 5000 repeated potential cycles, which is also ascertained for up to 48 h of operation at a constant potential by using a chronoamperometric technique with 28 % degradation in the current. The optimized material is utilized as a cathode catalyst in fabricating membrane electrode assembly for performance evaluation in an anion exchange membrane fuel cell. A peak power density of 12 mW cm À2 is realized in H 2 ÀO 2 feeds under ambient temperature and pressure; thus, it looks as an alternative non-preciousmetal catalyst for fuel cell applications. water (18.2 MW cm) used throughout the present work was produced from Milli-Q system, Germany.

The advancement of cost-effective, efficient, and durable catalysts to replace high cost Pt-based electrocatalysts are of recent interest, especially to enhance the sluggish oxygen reduction reaction (ORR) in fuel cells and metalÀ air batteries. Herein, we report self-assembled CoÀ Ni based nitrogen doped carbon structures (CoÀ Ni/NC) derived from zeolitic imidazolate frameworks as a highly efficient and durable ORR catalyst for rechargeable zincÀ air batteries (ZAB). An effective three-phase boundary is recognised with a well-organized interconnected porous carbon framework of the CoÀ Ni/NC catalyst. The developed catalyst exhibited much improved onset and halfwave potentials (0.93 V and 0.86 V vs. RHE, respectively) in alkaline electrolyte, especially in the limiting current region, which was credited to the porous structure. Furthermore, excellent durability was found for the catalyst operated using continuous potential cycles for 5,000 times and chronoamperometric measurements for 50 h. Finally, the optimised CoÀ Ni/NC catalyst was successfully utilised as a cathode catalyst and delivered substantial power density in ZAB configuration under ambient operating conditions. Substantial battery durability was also observed over 1000 h by periodically replacing the anodic zinc electrode. Hence, the present investigation offers the prospect of the development of new non-precious, highly active, and durable oxygen reduction catalysts for zinc air battery applications.

Clean technologies, which utilize or generate clean energy rather than fossil fuel-based energy, are under intense development to aid in addressing climate change. Current water desalination technologies are a growing user of fossil fuelderived electricity. A recently developed technology, termed the desalination fuel cell (DFC), can address this issue by instead using hydrogen gas to drive both feedwater desalination and green electricity generation simultaneously in a single cell. The main bottleneck is the use of Pt-based catalysts, which leads to high device costs and catalyst surface poisoning due to chloride ions (Cl − ) present in the feedwater. We here propose and demonstrate the first use of non-platinum group metal (non-PGM) catalysts toward DFCs. We synthesized a Fe/N/C based catalyst which demonstrated effective and Cl − tolerant oxygen reduction reaction ex situ and while used as a DFC cathode. The synthesis temperature and the metal concentrations were optimized using rotating disk electrode measurements, with an onset potential of up to 0.84 V vs RHE, on par with that of commercial Pt/C catalysts in a Cl − environment. When using the optimized Fe/N/C catalyst as a cathode in a prototype DFC, open circuit voltage was significantly improved relative to Pt/C, and measured cell voltage and desalination performance versus current density were nearly equivalent. Overall, these results show that non-PGM catalysts maintain or improve cell performance while significantly reducing cell costs, improving greatly the outlook for this nascent technology.

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