Increasing CO2 concentration in the atmosphere is believed to have a profound impact on the global climate. To reverse the impact would necessitate not only curbing the reliance on fossil fuels but also developing effective strategies capture and utilize CO2 from the atmosphere. Among several available strategies, CO2 reduction via the electrochemical or photochemical approach is particularly attractive since the required energy input can be potentially supplied from renewable sources such as solar energy. In this Review, an overview on these two different but inherently connected approaches is provided and recent progress on the development, engineering, and understanding of CO2 reduction electrocatalysts and photocatalysts is summarized. First, the basic principles that govern electrocatalytic or photocatalytic CO2 reduction and their important performance metrics are discussed. Then, a detailed discussion on different CO2 reduction electrocatalysts and photocatalysts as well as their generally designing strategies is provided. At the end of this Review, perspectives on the opportunities and possible directions for future development of this field are presented.

The development of nonprecious metal based electrocatalysts for hydrogen evolution reaction (HER) has received increasing attention over recent years. Previous studies have established MoC as a promising candidate. Nevertheless, its preparation requires high reaction temperature, which more than often causes particle sintering and results in low surface areas. In this study, we show supporting MoC nanoparticles on the three-dimensional scaffold as a possible solution to this challenge and develop a facile two-step preparation method for ∼3 nm MoC nanoparticles uniformly dispersed on carbon microflowers (MoC/NCF) via the self-polymerization of dopamine. The resulting hybrid material possesses large surface areas and a fully open and accessible structure with hierarchical order at different levels. MoO was found to play an important role in inducing the formation of this morphology presumably via its strong chelating interaction with the catechol groups of dopamine. Our electrochemical evaluation demonstrates that MoC/NCF exhibits excellent HER electrocatalytic performance with low onset overpotentials, small Tafel slopes, and excellent cycling stability in both acidic and alkaline solutions.

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