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.