Abstract
A substantial effort is devoted to the development of efficient electrolyzers made of earth-abundant elements for low-temperature industrial-scale water electrolysis. However, a large current density leads to the decline of the reaction kinetics that result from the decrease of local pH, the irreversible redox states of active metal sites, and the structure and composition collapse. Currently, the transition metal layered double hydroxides (LDHs) are proven as efficient alkaline oxygen evolution catalysts and demonstrate promising current density, generally at the scale of 10 mA cm–2 for the potential solar-driven catalysis concerning 10% solar-to-fuels efficiency. However, there is very limited progress in understanding the activity and stability degradation mechanism of LDHs at high current density, for instance above 100 mA cm–2. Here we introduce the current advances in achieving activity enhancement by tuning the composition, structure, and morphology of LDHs and present the degradation mechanism during the electrolysis under oxidative alkaline environments, long-term operation, and voltage fluctuations. Finally, we present the state-of-the-art approaches to stabilize the overall performance of LDHs for water oxidation and provide an outlook in this field.
Highlights
The oxygen evolution reaction (OER) is a very important halfreaction providing abundant electrons for electrochemical reduction reactions, such as nitrogen reduction reaction (NRR), carbon dioxide reaction (CO2RR), and hydrogen evolution reaction (HER)
This study reveals the importance of local pH at the vicinity of active sites and indicates that keeping the pH at the active sites strongly alkaline, for example, enabling faster diffusion, increases long-term stability
Layered double hydroxides are addressing more than a decadelong challenge to develop a nonprecious metal earth-abundant oxygen evolution catalyst
Summary
The oxygen evolution reaction (OER) is a very important halfreaction providing abundant electrons for electrochemical reduction reactions, such as nitrogen reduction reaction (NRR), carbon dioxide reaction (CO2RR), and hydrogen evolution reaction (HER). The main anode catalyst was made of Ru, Ir, or Ru−Ir oxides Such anodes can achieve an activity at 100−500 mA cm−2 in a concentrated aqueous solution of KOH or NaOH at ∼80 °C.3−6 the electrolysis plant has not yet achieved vigorous development, because of the high costs of the electrolyzers, absence of mass production, and limited market integration.[7,8] The cost of electrolyzers is estimated to drop exponentially in the following decade (Figure 1).[8] This requires reduction of cost by decreasing the component of the precious metals in catalysts, avoiding the expensive Ti support, developing alternative ionexchange membranes, and enhancing the up-scale catalyst synthesis approaches.[3,9] For example, using current technology, ∼40 years of Ir production has to be used to set up a system that could split water to generate hydrogen at a rate equivalent to 1 TW of energy storage.[10]. This review aims to provide insights into catalyst degradation and points out the issues that need to be resolved to apply those state-of-the-art catalysts in the emerging energy storage devices
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