Effective anodic sulfide removal catalyzed by single nickel atoms on nitrogen-doped graphene with stainless steel substrate

Abstract

Hydrogen sulfide is hazardous and life-threatening gas emission in anaerobic digestion and degradation. Electro-oxidation technology is a promising process for sulfide removal in aqueous media due to its high efficiency, cost effectiveness and easy operation. This study employed atomic nickel dispersed on nitrogen-doped graphene catalyst (A-Ni-NG) with stainless steel (SS) substrate for efficient sulfide removal. The results showed that the highest sulfide removal efficiency of 85.02±1.25% was achieved on SS/A-Ni-NG anode at 1.98 V (vs. RHE) in 48 h, which was 11.17% and 24.18% higher than that of bare SS and FTO/A-Ni-NG, respectively. SS/A-Ni-NG catalyst achieved a first-order rate constant of 0.036±0.001 h−1, improved by 24% compared with bare SS. The main products of sulfide oxidation were thiosulfate and elemental sulfur with Faradic efficiency of 32.37±3.20% and 18.99±0.05%, respectively. Electrochemical analysis showed the sulfide oxidation anodic peak potential on SS/A-Ni-NG anode was 280 mV (vs. RHE), lower than most of the reported graphite or Ni anodes. SS/A-Ni-NG improved the interface electric conductivity and the charge transfer rate, and directly catalyzed sulfide oxidation at applied voltage below oxygen evolution reaction (OER) onset potential. A-Ni-NG also indirectly removed sulfide by boosting OER at higher voltage. The superior sulfide oxidation catalytic activity of SS/A-Ni-NG anode was mainly attributed to the atomic dispersed Ni(I) generating NiOOH that boosted OER process and to the dopant N that induced activation region. A-Ni-NG coated on SS substrate is demonstrated to be a promising material for electrochemical sulfide removal.