Safeguarding CoMnMo-oxide nanosheets in acidic oxygen evolution reaction via an atomic layer deposited TiO2 conformal coating

Abstract

This study demonstrates a viable strategy to enhance the durability of transition metal oxide-based oxygen evolution reaction (OER) catalysts for electrochemical water splitting in acidic medium, offering a pathway toward more efficient and sustainable hydrogen production. While the designed CoMoO4/MnMoO4 heterojunction-based oxide nanosheets exhibit a promising catalytic activity for the OER, their stability suffers under acidic environments due to catalyst degradation and material dissolution, thereby limiting their long-term performance. To address this challenge, a thin conformal TiO2 film was deposited via atomic layer deposition (ALD) to prevent dissolution and deactivation of the catalytic properties of the underlying oxide. At the optimized 750 ALD cycles, the CoMoO4/MnMoO4/TiO2 heterostructure composite film achieves a benchmark OER overpotential of 260 mV to drive the electrolysis of 0.5 M H2SO4 solution at a current density of 10 mA.cm-2. The chronoamperometric and corrosion analysis revealed that the TiO2 coating on the CoMoO4/MnMoO4 nanosheets acted as a protective safeguard against corrosion in the aggressive acidic electrolyte, ensuring the long-term integrity of the catalyst for maintaining high catalytic performance. The results demonstrated that the TiO2 coated CoMoO4/MnMoO4 nanosheet-based film for 1000 ALD cycles exhibited significantly improved stability and sustained OER activity with a benchmark overpotential of 320 mV over an extended period of about 14 hours of electrolysis. The X-ray photoelectron spectroscopy and electrochemical analysis revealed that the deposited TiO2 and Mo sites of the CoMoO4/MnMoO4 interacted synergistically, enhancing the number of active catalytic sites, accelerating electron transfer, and extending the durability for the OER activity of the CoMoO4/MnMoO4.