The role of surface carbide/oxide heterojunction in electrocatalytic behavior of 3D-nanonest supported FeiMoj composites

Abstract

In this work, we synthesized iron-molybdenum composites with carbide and oxide functionalities and studied their catalytic activities towards the electrolysis of water and urea. A 3D carbon nano-nest (CnN) was synthesized as the carbide source as well as stabilizing agent for the bimetallic composite. In two different synthetic pathways, CnN was used as a co-precursor with metal salts and pre-synthesized bimetallic composite, respectively. The first path led to surface oxidized FeMo carbides (FMC-n) while the second path produced carbide corroborated FeMo-oxides (FM@C-n). The microscopic analyses indicated the presence of different metal phases with multivalency despite similar layered morphology. When used as electrode materials for water splitting and alkaline urea electrolysis, the materials showed different behavior; viz., FM@C− 1 showed the lowest overpotential for HER of 63 and 60 mV, while FMC-1 showed the lowest overpotential for anodic OER (270 mV) and UOR (1.445 V) for 10 mA cm−2, respectively. The reaction mechanism depended on the nature of the catalyst surface as well as the constituents. It was observed that the hydrogen evolution reaction at cathode depended on the nature of catalyst surface (carbide surface predominated over oxide), while the anode reactions were affected by the nature of metal center, indicating the direct interaction of intermediates with metal surfaces. The courses of reactions were studied through different microscopic analyses and the high activity and stability of the materials could be attributed to the surface defects, multivalency, and carbon support.