Anion‐Regulated Selective Generation of Cobalt Sites in Carbon: Toward Superior Bifunctional Electrocatalysis

Abstract

The introduction of active transition metal sites (TMSs) in carbon enables the synthesis of noble-metal-free electrocatalysts for clean energy conversion applications; however, there are often multiple existing forms of TMSs, which are of different natures and catalytic models. Regulating the evolution of distinctive TMSs is highly desirable but remains challenging to date. Anions, as essential elements involved in the synthesis, have been totally neglected previously in the construction of TMSs. Herein, the effects of anions on the creation of different types of TMSs are investigated for the first time. It is found that the active cobalt-nitrogen sites tend to be selectively constructed on the surface of N-doped carbon by using chloride, while metallic cobalt nanoparticles encased in protective graphite layers are the dominant forms of cobalt species with nitrate ions. The obtained catalysts demonstrate cobalt-sites-dependent activity for oxygen reduction reaction and hydrogen evolution reaction in acidic media. The remarkably enhanced catalytic activities approaching that of benchmark Pt/C in an acidic medium have been obtained on the catalyst dominated with cobalt-nitrogen sites, confirmed by the advanced spectroscopic characterization. This finding demonstrates a general paradigm of anion-regulated evolution of distinctive TMSs, providing a new pathway for enhancing performances of various targeted reactions related with TMSs.

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

“…The substrates of supported catalysts can be divided into traditional metal substrate, metal oxide substrate and new 2D material substrate. Many outstanding active metals of SACs, such as Pt [56,57], Au [58], Pd [59], Fe [60][61][62], Co [63][64][65], Ni [66] and Cr [67], have exhibited extraordinary activity in many catalytic reactions. There are also some common metal-oxide supporting substrates of SACs, such as FeO x [5], TiO 2 [68], ZrO 2 [69] and ZnO [70].…”

A review of anion-regulated multi-anion transition metal compounds for oxygen evolution electrocatalysis

“…[33][34][35][36] To date, Fe/Co/Nibased composites have become an important group of alternatives to precious metal OER catalysts. 9,12,13,24,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Other representative studies on cation-regulated OER catalysts include the etching of p-block metal ions in perovskite catalysts to provide abundant surface defects, 53 the modulation of the Ni redox properties in NiFe oxides by incorporating redox-inert Al 3+ ions, 54 the doping of W 6+ in FeCo oxyhydroxides, 55,56 and the integration of Cu + and Cu 2+ in copper oxides. 57 In addition to cation regulation, anion regulation on electrocatalysts has been gradually attracting increasing attention in recent years.…”

Atomically Transition Metals on Self‐Supported Porous Carbon Flake Arrays as Binder‐Free Air Cathode for Wearable Zinc−Air Batteries

“…The Co K‐edge X‐ray absorption near edge structure (XANES) spectra suggest the valence state of Co is between the Co 0 and Co 2+ states (Figure S7, Supporting Information). The Fourier‐transformed (FT) k 3 ‐weighted extended X‐ray absorption fine structure (EXAFS) spectra (Figure g) show that Co SA@NCF/CNF only exhibits a prominent peak at 1.41 Å, mainly attributed to the Co‐N/C first coordination shell, indicating that Co atoms are atomically coordinated by CN sites. The structural parameters by EXAFS fitting indicate that one Co atom is coordinated by four N atoms at 1.89 Å, forming a Co‐N 4 moiety …”