Abstract
Current research on catalysts for proton exchange membrane fuel cells (PEMFC) is based on obtaining higher catalytic activity than platinum particle catalysts on porous carbon. In search of a more sustainable catalyst other than platinum for the catalytic conversion of water to hydrogen gas, a series of nanoparticles of transition metals viz., Rh, Co, Fe, Pt and their composites with functionalized graphene such as RhNPs@f-graphene, CoNPs@f-graphene, PtNPs@f-graphene were synthesized and characterized by SEM and TEM techniques. The SEM analysis indicates that the texture of RhNPs@f-graphene resemble the dispersion of water droplets on lotus leaf. TEM analysis indicates that RhNPs of <10 nm diameter are dispersed on the surface of f-graphene. The air-stable NPs and nanocomposites were used as electrocatalyts for conversion of acidic water to hydrogen gas. The composite RhNPs@f-graphene catalyses hydrogen gas evolution from water containing p-toluene sulphonic acid (p-TsOH) at an onset reduction potential, Ep, −0.117 V which is less than that of PtNPs@f-graphene (Ep, −0.380 V) under identical experimental conditions whereas the onset potential of CoNPs@f-graphene was at Ep, −0.97 V and the FeNPs@f-graphene displayed onset potential at Ep, −1.58 V. The pure rhodium nanoparticles, RhNPs also electrocatalyse at Ep, −0.186 V compared with that of PtNPs at Ep, −0.36 V and that of CoNPs at Ep, −0.98 V. The electrocatalytic experiments also indicate that the RhNPs and RhNPs@f-graphene are stable, durable and they can be recycled in several catalytic experiments after washing with water and drying. The results indicate that RhNPs and RhNPs@f-graphene are better nanoelectrocatalysts than PtNPs and the reduction potentials were much higher in other transition metal nanoparticles. The mechanism could involve a hydridic species, Rh-H− followed by interaction with protons to form hydrogen gas.
Highlights
The three known classes of hydrogenases, [NiFe], [FeFe]- and FeS-cluster free hydrogenases contain iron at their active sites which are coordinated by thiolates, CO, CN− or a light sensitive cofactor[2]
Our research focused towards the electrochemical hydrogen evolution resulted in a mononuclear iron(III) dithiolene of severely distorted square pyramidal geometry and a nickel(II)-sulfur based radical ligand complex that catalyze electrochemical hydrogen gas evolution at lower potentials in CH3CN
The transition metal nanoparticles (TMNP, 1–3) were insoluble in water, they were sonicated in water and deposited on to polymer coated carbon grids and aluminum stubs for transmission electron microscopic (TEM) and scanning electron microscopic (SEM) analysis respectively
Summary
The three known classes of hydrogenases, [NiFe]-, [FeFe]- and FeS-cluster free hydrogenases contain iron at their active sites which are coordinated by thiolates, CO, CN− or a light sensitive cofactor[2]. Several other electrochemical hydrogen evolution catalysts have been reported including metalloporphyrins, low-valent transition metal complexes forming hydrides upon reaction with acids, mononuclear iron(II) complexes, cobalt-dithiolene complexes and a nickel complex [Ni(PPh2NPh)2][BF4]2 (PPh2NPh = 1,3,6-triphenyl-1aza-3,6-diphosphacycloheptane) which electrocatalyze H2 production with high turnover frequencies but at significantly high reduction potentials Ep > −1.1 V17–24. Our research focused towards the electrochemical hydrogen evolution resulted in a mononuclear iron(III) dithiolene of severely distorted square pyramidal geometry and a nickel(II)-sulfur based radical ligand complex that catalyze electrochemical hydrogen gas evolution at lower potentials in CH3CN. TiC is thermally stable with low solubility in sulfuric acid and high electronic conductivity Both these materials are used as supports for platinum and platinum– palladium alloy catalysts (Pt/TiC, Pt3Pd/TiC and Pt3Pd/TiC@TiO2) and their catalytic activity toward ORR are much higher than those for Pt/TiC38. In we report preparation, characterisation and electrocatalytic properties of rhodium nanoparticles (RhNPs) and graphene supported rhodium nanoparticles (RhNPs@f-graphene) which display better electrocatalytic performance than the platinum nanoparticles (PtNPs) and graphene supported platinum nanoparticles (PtNPs@f-graphene) under similar experimental conditions
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