Bifunctional non-noble metal oxide nanoparticle electrocatalysts through lithium-induced conversion for overall water splitting

TLDR

Developing earth‑abundant, active and stable electrocatalysts that function for both oxygen evolution and hydrogen evolution in a single electrolyte is crucial for renewable energy conversion. The study demonstrates that electrochemically converting ~20 nm transition‑metal‑oxide nanoparticles into 2–5 nm ultra‑small particles via lithium‑induced reactions enhances catalytic activity and yields bifunctional catalysts for overall water splitting. Lithium‑induced conversion preserves electrical interconnection among nanoparticles, generating large surface areas and numerous active sites while reducing particle size from ~20 nm to 2–5 nm. The resulting NiFeOx nanoparticles deliver 10 mA cm⁻² water‑splitting current at only 1.51 V for over 200 h in 1 M KOH, outperforming the Ir–Pt benchmark.

Abstract

Developing earth-abundant, active and stable electrocatalysts which operate in the same electrolyte for water splitting, including oxygen evolution reaction and hydrogen evolution reaction, is important for many renewable energy conversion processes. Here we demonstrate the improvement of catalytic activity when transition metal oxide (iron, cobalt, nickel oxides and their mixed oxides) nanoparticles (∼20 nm) are electrochemically transformed into ultra-small diameter (2-5 nm) nanoparticles through lithium-induced conversion reactions. Different from most traditional chemical syntheses, this method maintains excellent electrical interconnection among nanoparticles and results in large surface areas and many catalytically active sites. We demonstrate that lithium-induced ultra-small NiFeOx nanoparticles are active bifunctional catalysts exhibiting high activity and stability for overall water splitting in base. We achieve 10 mA cm(-2) water-splitting current at only 1.51 V for over 200 h without degradation in a two-electrode configuration and 1 M KOH, better than the combination of iridium and platinum as benchmark catalysts.