Electrosynthesis of highly efficient WO_3-x/graphene (photo-)electrocatalyst by two-electrode electrolysis system for oxygen evolution reaction

Integration of non-noble transition metal oxides with graphene is known to construct high-activity electrocatalysts for oxygen evolution reduction (OER). In order to avoid the complexity of traditional synthesis process, a facile electrochemical method is elaborately designed to engineer efficient WO_3-x/graphene (photo-)electrocatalyst for OER by a two-electrode electrolysis system, where graphite cathode is exfoliated into graphene and tungsten wire anode evolves into VO-rich WO_3-x profiting from formed reductive electrolyte solution. Among as-prepared samples, WO_3-x/G-2 shows the best electrocatalytic performance for OER with an overpotential of 320 mV (without iR compensation) at 10 mA/cm², superior to commercial RuO₂ (341 mV). With introduction of light illumination, the activity of WO_3-x/G-2 is greatly enhanced and its overpotential decreases to 290 mV, benefiting from additional reaction path produced by photocurrent effect and extra active sites generated by photogenerated carriers (h+). Characterization results indicate that both VO-rich WO_3-x and graphene contribute to the efficient OER performance. The activity of WO_3-x for OER is decided by the synergistic effect between VO concentration and particle size. The graphene could not only disperse WO_3-x nanoparticles, but also improve the holistic conductivity and promote electron transmission. This work supports a novel method for engineering WO_3-x/graphene composite for highly efficient (photo-)electrocatalytic performance for OER.