Advanced Materials for Electrochemical Energy Conversion and Storage

With the massive consumption of traditional fossil resources, environmental issues such as air pollution and greenhouse gas emissions have motivated a transition towards clean and sustainable energy sources capable of meeting the increasing energy demands of our modern society [1,2]. However, many renewable sources, such as wind, solar, geothermal, biomass, and hydropower, are intermittent and have to be converted into electrical energy to become an important portion of the energy supply system whilst also keeping carbon emissions low [3,4]. Therefore, electrochemical energy devices for the conversion and storage of electrical energy, including fuel cells, supercapacitors, batteries, etc., have sparked worldwide research interest, owing to the ambient operation conditions of a variety of energy sources.

The large-scale commercialization of electrochemical energy conversion and storage technologies strongly depends on the design and synthesis of stable and high-performing electrocatalyst and electrode materials [5,6]. Recently, tremendous progress has been achieved in the field of electrocatalytically converting abundant molecules on Earth (water, CO₂, and N₂) into value-added chemicals (hydrogen, hydrocarbons, and ammonia) with the development of novel low- and non-platinum electrocatalysts [7,8,9,10]. If we take the oxygen evolution reaction (OER) as an example for electrochemical energy conversion processes, various advanced electrocatalysts, including transition metal oxides, (oxy)hydroxides, chalcogenides, phosphides, and nitrides, have been proposed for OER [11]. The structure–performance relationship and the reaction mechanisms of the electrocatalysts, which are of great importance in future catalyst design, can be unraveled by means of both experimental and theoretical approaches. On the other hand, for energy storage devices (e.g., supercapacitors and metal-ion batteries), the structure–property regulation strategies of the electrode materials require elucidation through elaborate experimental measurements and theoretical simulations, comprising of the electronic structure, morphology, microstructure, heteroatom doping, defect engineering, heterointerface with electrically conductive supports, etc.

Despite great progress having already been contributed in regard to electrochemically promoted energy conversion and storage, challenges remain in the fabrication, characterization, and theoretical simulation of the electrocatalysts and electrodes. First, the precise control at the atomic and molecular levels for preparing stable and active functionalized materials is still difficult. The shape, architecture, size, and density of active centers essentially determine the electrochemical performance [12]; therefore, the fabrication approaches need to be further developed with precise and effective modulations of the morphology. Secondly, guidance from theoretical calculations, including the geometrical and electronic features of materials, the reacting sites and structures of intermediates, and the origin of the structure–property correlation, is still insufficient. More state-of-the-art technologies (i.e., machine-learning-based high-throughput screening) and more realistic computational models (i.e., at the mesoscopic scale) are expected to be utilized in the construction of novel materials, the explanation of experimental evidence, and the prediction of structure–property–performance relationships.

Overall, we hope this Special Issue can provide a platform for researches to share their findings and promote further investigations into the field of electrochemical energy conversion and storage.