Designing Multifunctional Cobalt Oxide Layers for Efficient and Stable Electrochemical Oxygen Evolution

Abstract

oxyhydroxides and oxides, have attracted significant interest as efficient and costeffective alternatives to noble-metal water-splitting electrocatalysts, with importance for commercialization of large-scale energy storage devices. [4][5][6] Generally, optimal electrocatalysts need to fulfil several requirements, including chemical stability for long-term operation, sufficient conductivity to enable charge transfer, and intrinsic activity of catalytic sites for efficient energy conversion. In the past decade, efforts have been devoted to material development and structural design of non-noble metal catalysts to enhance their electrocatalytic activities. In this context, disordered and porous materials provide higher activity given their increased concentrations of active sites and larger effective surface areas compared to their crystalline counterparts. [7,8] However, these materials often suffer from poor stability under operating conditions due to a variety of factors, including (electro)chemical susceptibilities and poor adhesion to the support structure. Therefore, catalyst-support integration and interface engineering play important roles for the realization of highly active and stable catalytic layers.Interface engineering is especially important for the integration of such electrocatalysts with semiconductor light absorbers for solar-to-chemical energy conversion. In this regard, interfacing semiconductor light absorbers with conformal and ultra-thin catalytic layers is a promising strategy to overcome the poor efficiency and material stability of the semiconductor photoelectrodes under harsh photoelectrochemical operating conditions. [1,[9][10][11][12][13][14][15] These multifunctional layers provide protection against corrosion in chemical environments and at the same time activate the desired catalytic reaction, while still permitting efficient interfacial charge transport and minimizing losses due to parasitic light absorption. However, simultaneously fulfilling each of these criteria requires precise control over film properties, often down to the sub-nm length scale. In this context, plasma-enhanced atomic layer deposition (PE-ALD) has emerged as a powerful method for designing surface and interface layers with tailored functionality and accurate thickness control. [12][13][14][15][16] In PE-ALD, the deposited precursor is exposed to highly reactive plasma radicals and thus less thermal energy is required to drive the surface chemistry compared to Disordered and porous metal oxides are promising earth-abundant and costeffective alternatives to noble-metal electrocatalysts. Herein, nonsaturated oxidation in plasma-enhanced atomic layer deposition is leveraged to tune the structural, mechanical, and optical properties of biphasic cobalt hydroxide films, thereby tailoring their catalytic activities and chemical stabilities. Short oxygen plasma exposure times and low plasma powers incompletely oxidize the cobaltocene precursor to Co(OH) 2 and result in carbon impurity incorporation. These Co(OH) 2 films...

Engineering Defects and Interfaces of Atomic Layer-Deposited TiOx-Protective Coatings for Efficient III–V Semiconductor Photocathodes

“…Having characterized the properties of the different ALD TiO x thin films, we now turn to the formation of InP/TiO x interfaces, which can be strongly affected by substrate oxidation during the ALD process. − Improved understanding of such surface oxidation is critical for realizing high-efficiency PEC devices since the formed oxide layer can not only present a resistance to interfacial charge injection but also lead to the formation of electronically active defects that increase trapping and recombination rates, especially in the case of plasma-enhanced processes. − Here, XPS measurements were performed following the deposition of 2 nm thick TiO x layers, which are sufficiently thin to enable the analysis of photoelectrons emitted from the InP/TiO x interface. Figure shows P 2p core level spectra obtained after the deposition of TiO x layers using TTIP combined with H 2 O or OP, compared with a bare InP wafer possessing a native oxide.…”

Progress in the Preparation of Metal Oxide Electrodes for the Electrochemical Treatment of Organic Wastewater: A Short Review

“…Compared with the above types of electrodes, metal oxide electrodes have higher catalytic activity and electrochemical stability [62][63][64], which can improve the reaction rate of the electrode. They not only have a longer service life, but can also be applied in a wide range of pH values.…”