Recent advances in multilevel nickel-nitrogen-carbon catalysts for CO2electroreduction to CO

As an emerging CO2 conversion technology, the electrochemical CO2 reduction (ECR) reaction has received widespread attention. For the ECR process, the accurate and rational design of electrocatalysts is essential and significant for improving the catalytic performance. Carbon-based materials are considered one of the promising electrocatalysts for ECR because of their variety of abundant sources, high specific surface area, high porosity, and multilevel dimensionality and tunable active sites. Furthermore, doping by heteroatoms and introducing metal atoms in the frameworks or substrates of the carbon materials are effective strategies for further improving the ECR activity. Particularly, nickel-nitrogen-carbon (Ni-N-C) materials show excellent reactivities for the ECR to CO and have the potential for large-scale applications. We summarize the recent development of Ni-N-C catalysts with a multilevel structure for the ECR to CO and also the key principles and primary parameters of the ECR. Furthermore, the rational and precise design of multilevel Ni-N-C catalysts on different carbon frameworks or substrates is discussed and presented, especially including carbon quantum dots, one dimensional (1D) carbon-based materials, two dimensional (2D) carbon-based materials and nanoporous carbon-based materials. The effects of microstructure on ECR performance are also analyzed. Finally, the challenges and outlook for Ni-N-C catalysts in an ECR system are presented. This review provides some new insights and guidelines for rationally designing and preparing Ni-N-C catalysts with a multilevel structure and high performance.