Facile fabrication of amorphous NiMo catalysts for alkaline hydrogen oxidation reaction

Abstract

The performance of HOR was improved due to the synergistic effect of alloying of Ni with Mo and the enhanced bifunctional effect through repeated potential cycling. • Binary Ni-Mo catalysts with various compositions are prepared via electrodeposition. • Prepared Ni-Mo catalysts are evaluated for HOR activity in alkaline media. • Ni 62 Mo 38 shows excellent catalytic activity and durability after repeated cycles. • This is attributed to the structural advantages and modified electronic structure. Abstract 1 1 Hydrogen oxidation reaction (HOR), anion exchange membrane fuel cell (AEMFC), proton exchange membrane fuel cell (PEMFC), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), KetjenBlack (KB), glassy carbon (GC), reversible hydrogen electrode (RHE), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). For the anion exchange membrane fuel cell (AEMFC), the development of non-precious hydrogen oxidation reaction (HOR) catalysts is crucial for overcoming cost-related limitations in commercialization. Among the non-precious HOR catalysts, NiMo catalysts with various compositions are studied. The composition of Mo is explored up to 45 % through the fast and facile electrodeposition technique. The prepared Ni x Mo 100-x catalysts have similar particle sizes and shapes, as well as amorphous structures owing to the adsorption of the citrate and Mo addition. Among the Ni x Mo 100-x catalysts, Ni 62 Mo 38 shows the highest HOR activity of 0.94 and 1.31 mA/cm 2 at 0.05 and 0.10 V RHE , respectively, in 0.1 M KOH solution. Additionally, the catalyst shows improved performance after the stability test (a maximum of 2.39 mA/cm 2 after 100 cycles and 2.02 mA/cm 2 after 3000 cycles at 0.10 V RHE , which are 111 % and 93.5 % of the initial performance of Pt/C, respectively), compared to its initial activity. This is superior to those of previously reported non-precious HOR catalysts, indicating its applicability to the AEMFC. This improved performance is attributed to the structural properties (amorphous and large electrochemical surface area), modified electronic structure of Ni by alloying with Mo, and strengthened bifunctional effect by repeated potential cycling.