Composition-dependent catalytic performance of Au_(x)Ag_(25-x) alloy nanoclusters for oxygen reduction reaction

Oxygen reduction reaction(ORR)occurs at the cathode of electrochemical devices like fuel cells and in the Huron-Dow process,reducing oxygen to water or hydrogen peroxide.Over the past years,various electrocatalysts with enhanced activity,selectivity,and durability have been developed for ORR.However,an atomic-level understanding of how materials composition affects electrocatalytic performance has not yet been achieved,which prevents us from designing efficient catalysts based on the requirements of practical applications.This is partially because of the polydispersity of traditional catalysts and their unknown structure dynamics in the electrocatalytic reactions.Here we establish a full-spectrum of atomically precise and robust Au_(x)Ag_(25-x)(MHA)18(x=0–25,and MHA=6-mercaptohexanoic acid)nanoclusters(NCs)and systematically investigate their composition-dependent catalytic performance for ORR at the atomic level.The results show that,with the increasing number of Au atoms in Au_(x)Ag_(25-x)(MHA)18 NCs,the electron transfer number gradually decreases from 3.9 for Ag25(MHA)18 to 2.1 for Au25(MHA)18,indicating that the dominant oxygen reduction product alters from water to hydrogen peroxide.Density functional theory simulations reveal that the Gibbs free energy of OOH adsorption(ΔGOOH*)on Au25 is closest to the idealΔGOOH*of 4.22 eV to produce H_(2)O_(2),while Ag alloying makes theΔGOOH*deviate from the optimal value and leads to the production of water.This study suggests that alloy NCs are promising paradigms for unveiling composition-dependent electrocatalytic performance of metal nanoparticles at the atomic level.

High electrocatalytic hydrogen evolution activity on a coupled Ru and CoO hybrid electrocatalyst

Hydrogen evolution reaction (HER) is an essential step in converting renewable energy to clean hydrogen fuel. Exploring highly efficient, stable and cost-effective electrocatalysts is of crucial significance for sustainable HER. Here, we report the design of a coupled ruthenium/cobalt oxide (Ru/CoO) hybrid electrocatalyst for alkaline HER. In this hybrid metal/oxide system, the complicated alkaline HER pathways are overall facilitated;oxygen (O)-vacancy-abundant oxide enhances water splitting and Ru promotes successive hydrogen intermediates to generate hydrogen. The resulting Ru/CoO hybrid electrocatalyst exhibits significantly promoted catalytic activity compared with benchmark Ru catalyst, displaying an overpotential of 55 mV to generate a HER current density of 10 mA cm^-2, comparable with the state-of-the-art Pt/C catalyst and the most efficient alkaline HER electrocatalysts. Furthermore, the strong interaction of Ru nanoparticles with oxide support and the in-situ growth of oxide support on conductive substrate guarantee the long-term stability of as-fabricated Ru/CoO hybrid electrocatalyst. This newly designed hybrid catalyst with abundant metal/oxide interfaces may pave a new pathway for exploring efficient and stable HER electrocatalysts.