Entropy-driven synthesis of CoB nanosheets for high-performance water splitting electrocatalysts

The development of efficient and durable alkaline water splitting electrocatalysts is vital for advancing the renewable hydrogen economy, a key pillar of sustainable energy systems. Here, we present an entropy-driven synthesis of phase-pure cobalt boride (CoB) nanosheets by a molten salt-assisted pyrolytic method. The obtained CoB, grown in situ on carbon cloth, can serve as an efficient electrocatalyst toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) simultaneously. Remarkably, it requires only overpotentials of 110 mV for HER and 240 mV for OER to drive a current density of 10 mA cm−2, respectively, addressing the critical need for cost-effective catalysts in renewable energy conversion. Experiments in combination with theoretical calculations reveal that interstitial B atoms can modulate the adsorption energy of Co sites and optimize the Co–H bond strength through the electron transfer between Co and B, thereby enhancing intrinsic HER activity. While in the OER, CoB nanosheets undergo in situ transformation into amorphous CoOOH, which acts as the highly active catalytic phase for the OER. This work not only provides a promising bifunctional electrocatalyst for alkaline water splitting but also offers fundamental insights into the catalytic mechanisms, paving the way for rational design of advanced electrocatalysts.