Tuning the Performance of Single-Atom Electrocatalysts: Support-Induced Structural Reconstruction

Abstract

Creating active and stable electrocatalysts remains a highly desirable and critical goal in the fields of catalysis and clean energy conversion. Single-atom catalyst (SAC), as a new research frontier in heterogeneous catalysis, has demonstrated emerging prospects for many electrocatalytic reactions. Supportassisted pyrolysis approaches are widely used in the synthesis of single-atom electrocatalysts. While extensive efforts have been devoted to increase the loading of the atomically dispersed metal sites, the role of the support in creating these active metal sites remains largely unexplored. Herein, we compare catalysts created by support-free and support-assisted pyrolysis of vitamin B12 and cobalt tetramethoxyphenylporphyrin, respectively, and demonstrate an important effect of support-induced structural reconstruction that directly controls the activation of SAC. Electrochemical studies show support-free catalysts are inactive for oxygen reduction reaction whereas the support-assisted pyrolysis yields highly active catalysts using the same molecular precursors. X-ray absorption spectroscopy experiments reveal that both the metal−nitrogen coordination and the type of nitrogen species are different in these two types of samples, which leads to a difference in the d-band of the cobalt metal center and ultimately controls the catalytic activity and stability. This new insight provides a unique perspective on how to tune the electrocatalytic performances of SAC at the molecular level.

Graphene-supported metal single-atom catalysts: a concise review

“…The chemical formula demonstrates the overall process of the ORR of the catalyst surface, including the ORR to directly generate H 2 O through an ideal four-electron pathway, or the formation of H 2 O 2 intermediate through an undesirable two-electron pathway. However, the high cost of the traditional Pt catalysts limits large-scale industrial applications [56,116,117]. Lefèvre et al [47] produced microporous carbon-supported iron-based catalysts, whose cathode current density could be comparable to that of platinum.…”

Modulating the Electronic Structure of Single‐Atom Catalysts on 2D Nanomaterials for Enhanced Electrocatalytic Performance

“…The above examples indicate that the neighboring atomic environment significantly influences the ORR activity of the isolated metal atoms. In a broader sense, the intrinsic activity of MN x moieties highly depends on the synergy between the single metal atoms and the supports . It was found that the addition of sulfur to the precursor gave an M‐N/C catalyst with enhanced ORR or fuel cell performance, but the mechanisms involved were still controversial .…”

Toward Efficient Carbon and Water Cycles: Emerging Opportunities with Single‐Site Catalysts Made of 3d Transition Metals

“…Reproduced with permission. [82] Copyright 2018, American Chemical Society. Reproduced with permission.…”

“…Based on their origins, they can be divided into three types: H 2 O 2 and/or reactive oxygen species (ROS) generated in the reaction, carbon oxidation occurring at high potentials and high temperature, and the instability of low-coordination M-N x sites. [82,[106][107][108] The side effect from H 2 O 2 /ROS on 3dTM-SSCs has been well established. During ORR reaction, aside from the four-electron reduction of oxygen to water, there is a competing twoelectron side reaction that yield H 2 O 2 or ROS as by-products.…”

“…The stability of 3dTM-SSCs also depends upon the local molecular coordination structure, which is highlighted in recent studies by a few groups. [82,109] It was found that support-free pyrolysis of macrocycle complexes of transition metals lead to metal center that resembles the coordination fragments of precursor, with abundant pyrrolic nitrogen sites and low coordination numbers. These systems are more susceptible to electrochemical dissolution in acid environment.…”