Enhanced electrocatalytic activity in hydrogen evolution reaction using 2D/2D nanohybrids of ruthenate nanoflakes and graphitic carbon nitride

Abstract

Photoelectrochemical and electrochemical water splitting was examined using ruthenate nanoflake (RuNF) and graphitic carbon nitride (g-C₃N₄) hybrids. A two-dimensional and visible-light-responsive photocatalyst g-C₃N₄ was hybridized with the RuNFs that we recently synthesized via a bottom-up process in aqueous solution, yielding 2D/2D nanocomposites. The influence of the 2D/2D nanocomposites on oxygen and hydrogen evolution during photoelectrochemical and electrochemical water splitting was investigated. First, electrolysis of a Na₂SO₄ aqueous solution was conducted with intermittent photo-irradiation. Both the g-C₃N₄ electrode and the RuNF/g-C₃N₄ hybrid electrode provided anodic and cathodic photocurrents at high and low potentials, respectively; however, the copresence of RuNFs decreased the photocurrents, probably because the RuNFs retarded the light absorption by g-C₃N₄. Moreover, the use of RuNF/g-C₃N₄ hybrids as electrodes facilitated both the oxygen and hydrogen evolution reactions without photo-irradiation. However, for the oxygen evolution reaction, the effect of the RuNFs was similar to that of RuO₂ nanoparticles, indicating that the influence of the type and morphology of ruthenium species on the oxygen evolution reaction was small. Conversely, irrespective of the pH of the aqueous solutions in an electrolytic bath, the 2D/2D nanostructure of RuNFs and g-C₃N₄ decreased the overpotential of the hydrogen evolution reaction. However, the use of RuO₂ particles instead of RuNFs did not cause such a phenomenon. Thus, it was revealed that the RuNFs synthesized via a bottom-up process were useful as a co-catalyst for the hydrogen evolution reaction.