Tailoring CoNi alloy embedded carbon nano-fibers by thiourea for enhanced hydrogen evolution reaction

Abstract

Toward the evolution of structure and composition of transition-metal based catalysts for hydrogen evolution reaction (HER), thiourea is utilized to tailor the size and distribution of CoNi alloy nanoparticles embedded in electrospinning carbon nanofibers (CoNi@CNFs). When adding appreciate dose of thiourea in the electrospinning precursor, the average grain size of CoNi nanoparticles reduces from 19.4 to 10.2 nm by the steric barrier effect of thiourea. Meanwhile, thiourea controls the favorable growth of CoNi on the surface of CoNi@CNFs. The surface CoNi alloy content increases from 25.1 to 34.6 wt %. The refining and well-dispersed CoNi nanoparticles improve the graphitization degree of carbon substrates. Furthermore, Thiourea provides S doping in CoNi alloy as well as the S, N doping in carbon substrates. The evolution of the structure and composition of CoNi@CNFs catalyst boosts the electronical performances by effectively modulating the electronic structure of the active sites, enlarge the exposure of active sites, and facilitate the electron transfer and mass diffusion. As a result, the optimized CoNi@CNFs (Thu-1.0) shows remarkable low overpotential (116 mV, 10 mA cm−2@1.0 mol KOH), outstanding hydrogen production rate (24.5 μmol/h, 20 mA cm−2@1.0 mol KOH), and superior stability (7.8% overpotential enlargement after 5000 continuous linear voltammetric cycles), when used as a catalyst material for HER application.