Advances and Perspective of Noble-Metal-Free Nitrogen-Doped Carbon for pH-Universal Oxygen Reduction Reaction Catalysts

Abstract

With the increasing demand for diversification of renewable energy sources, the high activity and stability of electrocatalysts in all pH ranges have been highlighted as one of the future directions in electrochemical energy generation and storage systems. Noble-metal-free nitrogen-doped carbon (M-N/ C) has been explored as a substitute for the expensive platinumbased oxygen reduction reaction (ORR) electrocatalysts. However, its ORR activity remains limited to alkaline electrolytes. In acidic medium, its low activity and stability correspond to metallic site dissolution and protonation of N-functional groups, which are even worse in neutral electrolytes because of low ionic conductivity and low H + concentration. This review summarizes strategies to improve the stability and activity of M-N/C as pH-universal ORR electrocatalysts. First, the ORR mechanism focusing on active site identification for each pH condition is discussed. Four strategies, including engineering pore structure, adding carbon shell wrapping, and introducing multiple nonmetal dopants and dual metallic active sites on the carbon substrate, are then evaluated to design pHuniversal ORR electrocatalysts with distinguished activity and stability. Lastly, future perspectives are given to show the viewpoint of further development and potential applications of M-N/C electrocatalysts.

Coordination engineering of atomically dispersed zirconium on graphene for the oxygen reduction reaction

“…It can be seen that all active sites preferably follow the 4e − pathway, which is favorable for many applications, like fuel cells and metal–air batteries. H 2 O 2 production will result in the degradation of the electrolyte membrane of proton exchange membrane fuel cells 37,38 and the corrosion of the metal anode in metal–air batteries. 39,40 The ORR performance is determined by the adsorption strength of each intermediate.…”

Perspectives of Wood-Inspired Electro-Fenton Catalysis for Energy-Efficient Wastewater Decontamination

“…Electrochemical O 2 reduction involves multiple processes in acidic media. Typically, the 4e – ORR pathway, which generates H 2 O as the final product, is considered the main competing reaction to the 2e – ORR pathway for H 2 O 2 generation. , During the ORR processes, O 2 molecules are initially adsorbed on the active sites of a catalyst. The adsorption mode of the O–O bond at the active sites determines the breakup behavior of the O–O bond, thus influencing the reaction pathways and products of ORR.…”

“…45 During the ORR processes, O 2 molecules are initially adsorbed on the active sites of a catalyst. The adsorption mode of the O−O bond at the active sites determines the breakup behavior of the O−O bond, thus influencing the reaction pathways and products of ORR.…”

Biomass‐Derived Electrocatalysts: Low‐Cost, Robust Materials for Sustainable Electrochemical Energy Conversion

“…[49,51] Importantly, the diverse nature of biomaterials also allows the codoping of other elements such as P and S during N-doping. [17,50,[57][58][59] The synergistic effects among multiple dopant atoms improve the chemical environment and conductivity, leading to superior electrocatalytic performance. [5,17,41,48] Consequently, these self-doped biocarbons are superior to regular carbons as supports and, even as metal-free catalysts, they exhibit high electrocatalytic activity that can rival metal-based catalysts.…”