Versatile Strategy for Tuning ORR Activity of a Single Fe-N<sub>4</sub> Site by Controlling Electron-Withdrawing/Donating Properties of a Carbon Plane

293

240

Carbon‐based heteroatom‐coordinated single‐atom catalysts (SACs) are promising candidates for energy‐related electrocatalysts because of their low‐cost, tunable catalytic activity/selectivity, and relatively homogeneous morphologies. Unique interactions between single metal sites and their surrounding coordination environments play a significant role in modulating the electronic structure of the metal centers, leading to unusual scaling relationships, new reaction mechanisms, and improved catalytic performance. This review summarizes recent advancements in engineering of the local coordination environment of SACs for improved electrocatalytic performance for several crucial energy‐convention electrochemical reactions: oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, CO2 reduction reaction, and nitrogen reduction reaction. Various engineering strategies including heteroatom‐doping, changing the location of SACs on their support, introducing external ligands, and constructing dual metal sites are comprehensively discussed. The controllable synthetic methods and the activity enhancement mechanism of state‐of‐the‐art SACs are also highlighted. Recent achievements in the electronic modification of SACs will provide an understanding of the structure–activity relationship for the rational design of advanced electrocatalysts.

Section: Atomically Dispersed Single Metal Site Electrocatalysis For mentioning

confidence: 99%

Section: Atomically Dispersed Single Metal Site Electrocatalysis For mentioning

confidence: 99%

Engineering Local Coordination Environments of Atomically Dispersed and Heteroatom‐Coordinated Single Metal Site Electrocatalysts for Clean Energy‐Conversion

Zhu

Sokolowski

Song

et al. 2019

293

240

“…The experiment and DFT calculation have demonstrated that the OER catalysts following the activity tendency of Ni > Co > Fe. Lee and co‐workers have reported that S‐doping can incorporate electron‐donating/withdrawing function in carbon plane, which can change the charge state of the FeN 4 and provide an optimal intermediates adsorption energy, and thus accelerate the ORR reaction …”

Section: Intramolecular Charge Transfermentioning

confidence: 99%

Charge Transfer Modulated Activity of Carbon‐Based Electrocatalysts

Wang

Zou

et al. 2019

190

Electrocatalysis is the most important electrode reactions for many energy storage and conversion devices, which are considered a key part of the resolution of the energy crisis. Toward this end, design of efficient electrocatalysts is of critical significance. While extensive research has been extended to develop excellent electrocatalysts, the fundamental understanding of the relationship between the electronic and structural properties of electrocatalysts and the catalytic activity must remain a priority. In this review, the activity modulation of electrocatalysts by charge transfer effects, including intramolecular and intermolecular charge transfer, is systematically introduced. With suitable charge transfer modification, such as heteroatom doping, defect engineering, molecule functionalization, and heterojunctions, the electrocatalytic activity of carbon‐based electrocatalysts can be significantly boosted. The manipulation of the electronic structure of carbon‐based materials by charge transfer may serve as a fundamental mechanism for performance enhancement. After establishing an understanding of the relationship between catalytic activity and charge transfer, the opportunities and challenges for the design of electrocatalyst with charge transfer effects are discussed.

“…Mun et al report a versatile strategy to incorporate electron‐withdrawing/donating functionalities on the carbon plane by S‐doping ( Figure 4 ). The strength of the electronic effect, derived from the delocalized π‐band of the carbon plane on the d‐orbital of the Fe ion in the Fe–N 4 site results in a beneficial change of ORR activity of the Fe–N 4 site …”

Section: Iron‐based Electrocatalystsmentioning

confidence: 99%

“…The thiophene‐like S functionality gives an electron‐donating effect, and the oxidized S functionality gives an electron‐withdrawing effect to the Fe–N 4 site. Adapted with permission . Copyright 2019, ACS.…”

Section: Iron‐based Electrocatalystsmentioning

confidence: 99%

Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

Sharifi

Gracia‐Espino

Chen

et al. 2019

The oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O2 adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.