Ultrasmall Metal Nanoclusters As Bifuntional Electrocatalysts for Overall Water Splitting

Abstract

Splitting water into hydrogen and oxygen is one of the key processes for renewable energy production. Electrocatalytic water splitting composed of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is considered to be a viable method due to its high efficiency and strong connectivity to energy-related electrodevices. Consequently, development of water splitting electrocatalysts is emerging field spanning from traditional Pt group metals to non-precious metal based catalysts. Ligand-protected metal nanoclusters could be one of the candidates because of their uniformity, stability and distinctive catalytic activity. Here we report electrocatalytic activity of atomically precise Mx(SR)y (M = metal, SR = thiolate) nanoclusters for water splitting reactions. HER activities were investigated by linear sweep voltammetry (LSV) and constant potential electrolysis (CPE). Metal nanoclusters exhibited distinctive HER activity with low Tafel slopes for universal pH range (pH 1 – 14). The activity could be modified by controlling the number of metals and ligands with atomic precision. OER activities of metal nanoclusters were examined by LSV and showed higher catalytic current than commercial IrO2 in alkaline media. Furthermore, metal nanoclusters were used as bifunctional water splitting (HER/OER) catalysts that showed high current density (100 mA cm-2) at a low electrochemical cell potential (2.5 V).