Metal-Oxygen Hybridization of Bi/Bife(oxy)Hydroxide for Sustainable Lattice Oxygen Mechanism at High Current Density

Abstract

Hydrogen energy production through the electricity-driven water electrolysis has been broadly studied to deal with growing energy demands and environment pollutions. Oxygen evolution reaction (OER) which is the half anodic reaction of water electrolysis determines overall water electrolysis due to OOH* coordination with high energy barrier. Recently, alternative reaction kinetics detouring sluggish OOH intermediate in OER pathway has been proposed as breakthrough for efficient water electrolysis. That is the strategy which directly conjugates activated lattice oxygen species to form O-O coupling instead of OOH intermediate. However, absence of facile method to realize lattice oxygen activation and structural instability during OER cycles remain as challenge, hindering practical applications of water electrolysis. In this work, metal-oxygen hybridization method has been demonstrated as not only a simple and facile strategy to activate lattice oxygen species but also sustain lattice oxygen mechanism (LOM) during OER cycles at a practical current density (> 1000 mA cm-2). Using redox potential difference between bismuth (Bi) and iron (Fe) as driving force, galvanic replacement and Kirkendall effect take place in binary metal system, resulting in heterostructure composed of amorphous BiFe(oxy)hydroxides and molecular bismuth (Bi) metal nanoparticles (BM/BiFeOxHy) with abundant oxygen non-bonding states. In 1 M KOH solution, the BM/BiFeOxHy electrocatalyst requires low overpotential of 232 and 359 mV at the current densities of 10 and 1,000 mA cm-2, respectively. Moreover, long-term catalytic stability is demonstrated up to 1,000 hours at a practically high current density of 1,000 mA cm-2 without significant degradation by virtue of the balanced hybridization of Bi/Fe-O. Electrochemical/physicochemical analysis and density functional theory (DFT) calculation reveal that the excellent OER performance and stability of BM/BiFeOxHy electrocatalyst are attributed to the optimized Fe/Bi-O hybridization and resulting heterostructure with increased oxygen non-bonding states.