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Oxygen reduction reactions (ORRs) are unanimously a key factor of system performances in bioelectrochemical systems (BESs), low-temperature fuel cells, and generally in several electrochemical platforms. Platinum (Pt)-based catalyst is the finest electrocatalyst for ORR in BESs; however, it is constrained by its low abundance, high price, and poor catalytic durability in an electrochemical setup for cathodic reaction kinetics. In recent years, significant efforts in trimming the metal-based catalyst up to nanoscale to cater high performance of ORR have been explored. Still, there are many opportunities to improve catalyst performance at cathode through proper selection of an efficient low-cost metal-based ORR catalyst. Molybdenum (Mo) with its multi-dimensional form as 2D and 3D layers and synergistic combination with other non-metals offers prospects of extraordinary performance as low-cost metal-based ORR catalyst over the Pt in delivering enhanced ORR potential. The present review throws light on current requirements of a sturdier catalyst material and thus provides a comprehensive review on the continuing efforts in exploring the possibility of Mo as a low-cost metal-based ORR catalyst. This literature analysis would enlighten the significance of ORR in BESs, followed by the electrochemistry of Mo-based cathodic catalyst, its underlying mechanism and performance limiting factors in the operation of ORR. Moreover, the extensive and systematic acumen in the context of Mo-based catalytic formulations for increased ORR potentials including nano-composite Mo-cathode catalyst; development of Mo-catalyst with varied configurations; carbon-supported Mo-catalyst; morphological changes; surface area modifications; and Mo-coupling with other transition metal and its derivatives were discussed in great detail to provide prospective application of Mo-based catalyst. Lastly, numerous opportunities and projections for future research in fabrication, juxtaposition, and implementation of Mo-based cathodic catalysts and consequent recommendations were discussed as conclusive remarks for bringing out the state-of-the-art review on this subject. [ABSTRACT FROM AUTHOR]

Ordered mesoporous carbon (OMC) supported Pt catalysts were prepared by different loading techniques, in order to be used in the catalysis of oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. OMC was synthesized by an organic-inorganic self assembly route using Pluronic F127 as surface directing agent, resorcinol-formaldehyde as carbon source and tetraethyl ortosilicate (TEOS) as silica source. Pt loading was achieved by three different approaches; one pot in situ synthesis, wet impregnation and surface-modified wet impregnation. Nitrogen adsorption studies showed slight reductions in surface areas, which can be attributed to partial losses of micropore volumes. The XRD and TEM analysis revealed a better metal distribution and smaller particle size in the surface-modified sample with a mean Pt particle size of 3.83 nm. The modified sample also gave the most promising performance among the catalysts with a maximum power density of 73 mW cm−2, which was very close to the commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The development of high efficient cathode catalyst is known to be very important for the large-scale application of fuel cells. In this work, by using the density functional theory, metal-porphyrin (M = Mn, Co) carbon materials (Mn/CoN4-C) have been investigated as possible oxygen reduction reaction (ORR) catalysts. The calculated formation energies indicate that Mn/CoN4-C is stable thermodynamically. For MnN4-C, ORR proceeds with a four-electron process. While for CoN4-C, both two-electron pathway and four-electron pathway are competitive, with the former being slightly favoured. For both compounds, the O2 hydrogenation pathway is favoured compared with O2 dissociation pathway. In CoN4-C, the energy barrier is 0.13 eV for the two-electron pathway, while it is 0.47 eV for the four-electron pathway, much lower than 0.80 eV for pure Pt. These energy barriers are also much lower than that in MnN4-C, showing that CoN4-C has a better ORR activity than MnN4-C. The calculated working potential is 0.30 eV for CoN4 in the four-electron pathway. [ABSTRACT FROM AUTHOR]

Metal-nitrogen/carbon (Me-N/C) coordination is the most alternative to Pt/C catalyst for oxygen reduction reaction (ORR). In this work, we utilized carbon nanotube (CNT) as carriers, synthesized Fe@CNT-Fe/N/C via high temperature. The Fe@CNT-Fe/N/C catalyst has a tubular structure, which can well coat the metal particles in the tube, protect the metal particles from corrosion by the acidic solution, and maintain the long-term effectiveness of the catalyst. Fe-Nx and Fe3C structures are the ORR active centers of the catalyst, and Fe-Nx and Fe3C coexist to promote the oxygen reduction reaction activity. The as-prepared catalyst possesses high ORR catalytic activity as well as good stability. [ABSTRACT FROM AUTHOR]

The dissociation of O2and HO2are important reactions that occur at the cathode of fuel cells and require catalysts to proceed. There is a need to replace the presently used platinum catalyst with less expensive materials. Modelling has been used to identify potential two-dimensional catalysts such as boron- and nitrogen-doped graphene. Here, the possibility of boron nitride nano-ribbons and nano-tubes which do not require doping are considered. Density functional calculations are used to show that O2and HO2can bond to zig–zag and armchair boron nitride nano-ribbons and nano-tubes. The bond dissociation energies (BDEs) to remove an O and an OH from O2and HO2bonded to the boron nitride ribbons and tubes are calculated and are a measure of the catalytic effectiveness of the boron nitride structures. The results show that both the zig–zag and armchair boron nitride ribbons could be a catalyst for HO2dissociation but not O2dissociation. However, zig–zag boron nitride nano-tubes are shown not to be effective catalysts for the dissociation of O2or HO2.An armchair boron nitride nano-tube is shown to have a very low BDEs to remove OH from HO2bonded to it and could be an affective catalyst. [ABSTRACT FROM PUBLISHER]

Fuel cell (FC) test results have been obtained for the first time with the bis-ligand nickel(ii) complex of 1,4-diaza-3,7-diphosphacyclootane heterogeneous catalyst. Using AFM technique the [Ni(PPh2Np-Tol2)2](BF4)2self-assemblies morphology on pyrolytic graphite has been studied. By the method of rotating disk electrode the mechanism of FC cathode side reaction has been investigated [ABSTRACT FROM PUBLISHER]