Altering Ligand Fields in Single-Atom Sites through Second-Shell Anion Modulation Boosts the Oxygen Reduction Reaction

Abstract

Single-atom catalysts based on metal−N 4 moieties and anchored on carbon supports (defined as M−N−C) are promising for oxygen reduction reaction (ORR). Among those, M−N−C catalysts with 4d and 5d transition metal (TM 4d,5d ) centers are much more durable and not susceptible to the undesirable Fenton reaction, especially compared with 3d transition metal based ones. However, the ORR activity of these TM 4d,5d −N− C catalysts is still far from satisfactory; thus far, there are few discussions about how to accurately tune the ligand fields of singleatom TM 4d,5d sites in order to improve their catalytic properties. Herein, we leverage single-atom Ru−N−C as a model system and report an S-anion coordination strategy to modulate the catalyst's structure and ORR performance. The S anions are identified to bond with N atoms in the second coordination shell of Ru centers, which allows us to manipulate the electronic configuration of central Ru sites. The S-anion-coordinated Ru−N−C catalyst delivers not only promising ORR activity but also outstanding longterm durability, superior to those of commercial Pt/C and most of the near-term single-atom catalysts. DFT calculations reveal that the high ORR activity is attributed to the lower adsorption energy of ORR intermediates at Ru sites. Metal−air batteries using this catalyst in the cathode side also exhibit fast kinetics and excellent stability.

Recent Advances in Dual‐Atom Site Catalysts for Efficient Oxygen and Carbon Dioxide Electrocatalysis

“…Unsaturated coordination environments, unique electronic structures and quantum size effect bring SACs widespread application as well as distinguished catalytic performance beyond our expectation. [ 11 ] Benefited from these advantages, SACs have been extensively applied in electrocatalytic reactions, such as ORR, [ 16–18 ] OER, [ 19–21 ] and CO 2 RR. [ 22–24 ]…”

“…Unsaturated coordination environments, unique electronic structures and quantum size effect bring SACs widespread application as well as distinguished catalytic performance beyond our expectation. [11] Benefited from these advantages, SACs have been extensively applied in electrocatalytic reactions, such as ORR, [16][17][18] OER, [19][20][21] and CO 2 RR. [22][23][24] Although SACs exhibit particular advantages, some intrinsic defects limit their further development: (1) when it comes to complex processes involving multiple reactive intermediates, all of them are adsorbed on the same active center.…”

Macro/Micro‐Environment Regulating Carbon‐Supported Single‐Atom Catalysts for Hydrogen/Oxygen Conversion Reactions

“…), will induce the modification of center metals beyond the first shell, resulting in the modified electronic structure of metal sites via long-range delocalization, which provides fine-tuning strategies of the intrinsic catalytic activity. [24,25] Some reviews about SACs have been reported regarding the synthetic strategies, characterization methods, support selection, coordination environments, and anchoring site design. [14,[26][27][28] A number of review papers have been published on the application of SACs for energy conversion reactions, and they have summarized the synthetic strategies, characterization methods, substrate effects, and inner relationships between the tunable microenvironments and catalytic activities, etc.…”

“…), will induce the modification of center metals beyond the first shell, resulting in the modified electronic structure of metal sites via long‐range delocalization, which provides fine‐tuning strategies of the intrinsic catalytic activity. [ 24,25 ]…”

Boosting the oxygen reduction reaction behaviour of atomic Fe–N4active sites in porous honeycomb-like carbonviaP heteroatom doping

“…[21][22][23][24][25][26][27] The atomic TM-N 4 moieties are active sites that directly adsorb O 2 and the related ORR intermediates, and the binding energies of which are governed by the nature of the TM in TM-N 4 . [28][29][30] According to some pioneering studies, the widely investigated Fe-N 4 active sites in SACs usually have a strong combination with OOH*, O*, and OH* for ORR, which are troublesome for the desorption of ORR-related intermediate products, leading to the attenuation of catalytic efficiency. 31,32 Many attempts have been made to improve their catalytic properties toward ORR, focusing on the regulation of the coordination environment of the metal atomic centres of SACs.…”