Facile fabrication of ultrafine nickel-iridium alloy nanoparticles/graphene hybrid with enhanced mass activity and stability for overall water splitting

Abstract

• A facile and general method was developed for fabricating Ni-Ir alloy nanoparticles/graphene electrocatalysts. • The incorporation of Ir into metallic Ni lattice greatly improves the intrinsic activity for HER and OER. • The bifunctional catalyst shows much higher electrochemical performance than commercial 20 wt% Ir/C. Developing active and durable electrocatalysts for overall water splitting is desirable but challenging to realize sustainable hydrogen production. Here, we report a facile and general method to prepare ultrafine nickel (Ni)-iridium (Ir) alloy nanoparticles/graphene hybrids for overall water splitting. The optimized hybrid with 4.9 wt% Ir exhibits much higher catalytic activity and durability than commercial 20 wt% Ir/C for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Theoretical simulations reveal that the incorporation of Ir in metallic Ni lattice regulates hydrogen adsorption free energy to the optimum level, thus improving HER activity, while in situ generated amorphous Ir-Ni hydr(oxy)oxides around metallic Ni-Ir core have been demonstrated to be the active species under OER conditions, which switches OER rate-determining step to energy-favorable pathway. The overall water splitting electrolyzer assembled by the optimized electrocatalyst shows a low cell voltage of only 1.52 V and excellent stability to deliver a current density of 10 mA cm −2 . This work provides a powerful strategy toward general synthesis of ultrafine alloy nanoparticles for high-performance overall water splitting. Ultrafine nickel-iridium alloy nanoparticles/graphene hybrids serve as highly efficient bifunctional electrocatalysts for overall water splitting. The incorporation of Ir greatly improves the reaction kinetics for hydrogen evolution reaction and oxygen evolution reaction.