Honeycomb-structured S and N-codoped highly graphitized carbon as a catalyst support for Rh nanoparticles: A new benchmark electrocatalyst for hydrogen evolution reaction

Abstract

State-of-the-art electrocatalysts are based on catalytically active metal deposited on conductive porous carbon. Herein, we report a new strategy of engineering of a honeycomb-structured S and N dual-doped graphene-like carbon (SNG) as a supporting material for Rh catalysts by a simple low-temperature (850 °C) pyrolysis of S-doped carbon nitride (S-CN) in the presence of Mg. Interestingly, here Mg plays a marvelous dual role not only as a reducing agent for graphitizing the S-CN but also as a precursor for new Mg3N2 and MgS products, which play as pore-generating templates for honeycomb-like structures. This features highly robust graphitized carbon with excellent electrical conductivity, proper S and N content, and porosity, making it highly desirable as catalyst support. Supporting Rh (5.2 wt.%) on SNG outperforms state-of-the-art commercial Pt/C electrodes for hydrogen evolution reaction (HER) under alkaline settings (1.0 M KOH) with an extremely lower overpotential of 13 mV at 10 mA cm−2, a lower Tafel value, and a higher turnover frequency. In addition, Rh/SNG as the cathode for industrial water electrolysis in 6.0 M KOH electrolyte at 70 °C shows excellent performance with only 1.76 Vcell to achieve 500 mA cm−2 and maintains long-term durability with negligible decay. The distinctive properties of SNG, including S and N dual doping, high graphiticity, superior electrical conductivity, and honeycomb-like hierarchical meso‑ and macropore structure, are credited with this remarkable HER performance. The S and N dopants in the SNG framework optimize the electronic structure of the Rh by synergistic interaction between them as illustrated by first-principal density functional theory calculations and electronic structure analysis.