In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.

great potential to meet our ever-growing demand for energy. These devices appear most promising due to their high energyconversion and storage efficiencies, portability, which can mitigate the intermittent distribution of the aforementioned energy in space and time, and environmental benignancy. [6][7][8][9][10] Fundamentally, these electrochemical systems or devices involve different energy-conversion reactions, such as the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and electrochemical CO 2 reduction (ECR), which provide energy by directly converting chemical energy (e.g., methanol, ethanol, zinc, and hydrogen) into electrical energy, or store energy vice versa. [6][7][8][9][10][11][12] The intrinsically sluggish kinetics of these reactions highlights the critical role of electrocatalysts. In this regard, the development of advanced electrocatalysts has always been the technological bottleneck that hinders the practical applications of these energy techniques at any appreciable scale. [7][8][9][10][11][12] Currently, noble-metal-based materials (e.g., Pt, IrO 2 , RuO 2 , and Au) are considered to be state-of-the-art catalysts for a variety of energy devices, [13][14][15][16] such as proton exchange membrane fuel cells (PEMFCs). [13] In spite of their outstanding catalytic performance for many electrochemical reactions, the high cost and scarcity of these noble metals severely hamper their large-scale commercialization. [17] Further, precious metal catalysts face issues with poisoning when exposed to a range of chemical compounds like methaol and carbon monoxide, leading to significant activity loss. [18] Therefore, extensive studies have focused on the development of alternative electrocatalysts with high activity, long stability, low cost, widespread availability, and facile synthesis. [8][9][10]19,20] To replace precious-metal-based catalysts, a wide range of non-noble-metal materials, especially transition-metal-based materials and metal-free carbon materials, have been intensively investigated as electrocatalysts for different applications. [21] Most of these electrocatalyst candidates show great promise in energy-conversion reactions. Nevertheless, very few alternative materials have yet to achieve superior electrochemical properties to those of noble-metal-based catalysts. Fortunately, the accumulation of experimental and theoretical studies have significantly advanced our knowledge on the chemical and physical nature of various candidate materials. [10][11][12] For example, our group has shed light on the activity origin of The key challenge to developing renewable and clean energy technologies lies in the rational design and synthesis of efficient and earth-abundant catalysts for a wide variety of electrochemical reactions. This review presents materials design strategies for constructing improved electrocatalysts based on MOF precursors/templates, with special emphasis on component manipulation, morphology control, and structure engineering. G...

The replacement of precious-metal-based catalysts with earth-abundant alternatives for a diverse range of electrochemical applications is of great importance for next-generation energy technologies. Many self-supported earth-abundant nanoarrays have emerged as state-of-the-art electrocatalysts due to their fascinating structures and electrochemical properties. This Review presents recent advances made toward developing self-supported earth-abundant nanoarrays for a wide range of energy-conversion processes. We summarize the different synthetic methods used to construct nanoarrays and tune their compositions, morphologies, and structures. Then, we highlight their application and performance as catalysts for various energy-related reactions. We also discuss their ability to perform as bifunctional electrocatalysts in energy devices. Finally, we conclude with the challenges and prospects in this promising field, where further exploration into these materials will facilitate the development of next-generation energy technologies.

A two-dimensional metal-organic framework (MOF) comprising nickel species and an organic ligand of benzenedicarboxylic acid is fabricated and explored as an electrocatalyst for urea oxidation reaction (UOR). The excellent UOR performance is found to be partially due to the high active site density of the two-dimensional MOF, and largely because of the high oxidation state of the nickel species.

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