Amorphous structures for enhancing the electrochemical activity of nickel disulfide for efficient methanol oxidation

Abstract

Direct methanol fuel cells (DMFCs) hold great promise for portable power applications as an efficient carbon-neutral technology, which are largely restricted by the inherently poor kinetics of the methanol oxidation reaction (MOR). To date, amorphous catalysts have been widely applied to boost the electro-oxidation process, but there is nevertheless a lack of in-depth understanding of the efficacy of the amorphous structure on the promotion of MOR performance. Herein, we highlight a facile microwave-assisted strategy to synthesize amorphous and crystalline NiS₂ nanospheres by varying the type of sulfur source, and subsequently employ them as available catalysts for the MOR. Notably, taking the amorphous and crystalline NiS₂ catalysts as a promising platform, the underlying relationship between the amorphous structure and the MOR is deeply investigated by means of theoretical simulations and experimental measurements. Benefiting from its condensed active sites and increased intrinsic reactivity closely associated with optimized reaction kinetics for the formation of NiOOH species, the amorphous NiS₂ catalyst possesses superior electrochemical MOR activity over the crystalline counterpart, affording a large current density of 200 mA cm⁻² at a potential of 0.6 V vs. Ag/AgCl. This work can provide guidelines in the design and optimization of highly active MOR electrocatalysts.