Controlling edge active sites by vulcanizing a bimetallic hydroxide for boosting the oxygen evolution reaction

Abstract

Sulfur-laden wastewater can serve as a valuable resource for synthesizing transition-metal sulfide (TMS) electrocatalysts to address the sluggish kinetics of the oxygen evolution reaction (OER) in water splitting, which is a significant issue affecting environmental and energy advancements. However, TMSs suffer from intrinsic constraints, particularly a prevalence of catalytically inert basal planes that impede their efficacy. To solve this issue, herein, CoNi–S/CoNi(OH)₂ nanosheets on nickel foam (NF) were constructed employing sodium ethyl xanthate (synthesized using sulfur-containing wastewater) to partially vulcanize CoNi(OH)₂ for improving the OER performance. In situ formed Co₉S₈–Ni₃S₂ on CoNi(OH)₂ nanosheets provide a high density of edge active sites, compensating for the inert basal planes. Due to the bridging effects of S²⁻ and O²⁻, the electronic redistribution is conducive to forming Ni³⁺, thereby facilitating a phase transformation from CoNi–S/CoNi(OH)₂ into active S-containing CoNiOOH. Density functional theory calculations verify that incorporating S into CoNi(OH)₂ leads to rich edge catalytic sites and modulates the adsorption/desorption of oxygen-containing intermediates, significantly reducing the energy barrier of the potential-determining step during the OER process. Additionally, the stability of CoNi–S/CoNi(OH)₂ was enhanced by the strengthened M–S (M = Co, Ni) bonds via π donation to Mⁿ⁺ from S²⁻ and O²⁻. All these features endow CoNi–S/CoNi(OH)₂ with a low overpotential of 295 mV at 20 mA cm⁻² with a Tafel slope of 58 mV dec⁻¹. This work presents a strategy for utilizing sulfur-containing wastewater in clean energy applications.