Ultrafine carbon encapsulated NiRu alloys as bifunctional electrocatalysts for boosting overall water splitting: morphological and electronic modulation through minor Ru alloying

Abstract

Encapsulating metallic nanoparticles (NPs) with a graphitic carbon shell is a promising strategy to achieve highly efficient and stable electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and electrochemical overall water splitting (OWS). This work presents a simple and facile synthesis of graphitic carbon coated Ni_xRu_y alloys. The optimized catalyst (e-Ni_0.6Ru_0.4@C) displays an ultrafine morphology and outstanding HER and OER activities in alkaline media, which are among the best reported so far for various carbon-based electrocatalysts. Remarkably, the e-Ni_0.6Ru_0.4@C‖e-Ni_0.6Ru_0.4@C pair needs a low cell voltage of 1.51/1.62 V for driving OWS to reach 10/100 mA cm⁻², far outperforming the benchmark electrode pair Pt/C‖RuO₂. As expected, this carbon-based catalyst also exhibits superior durability as compared to that of precious catalysts. The experimental evidence combined with density functional theory (DFT) computations thus demonstrates for the first time that minor Ru alloying enables not only the morphological modulation but also the fine electronic modification of the catalyst, which both facilitate the overall electrochemical reactions on the carbon shell surface. Thus, our results may further shed light on how to design and optimize carbon-based electrocatalysts to achieve enhanced catalytic performance for OWS.