Tao Luo

Abstract Single-atom Fe-N-C catalysts has attracted widespread attentions in the oxygen reduction reaction (ORR). However, the origin of ORR activity on Fe-N-C catalysts is still unclear, which hinder the further improvement of Fe-N-C catalysts. Herein, we provide a model to understand the ORR activity of Fe-N 4 site from the spatial structure and energy level of the frontier orbitals by density functional theory calculations. Taking the regulation of divacancy defects on Fe-N 4 site ORR activity as examples, we demonstrate that the hybridization between Fe 3 dz 2 , 3 dyz (3 dxz ) and O 2 π* orbitals is the origin of Fe-N 4 ORR activity. We found that the Fe–O bond length, the d-band center gap of spin states, the magnetic moment of Fe site and *O 2 as descriptors can accurately predict the ORR activity of Fe-N 4 site. Furthermore, these descriptors and ORR activity of Fe-N 4 site are mainly distributed in two regions with obvious difference, which greatly relate to the height of Fe 3 d projected orbital in the Z direction. This work provides a new insight into the ORR activity of single-atom M-N-C catalysts.

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Abstract Heteroatom‐doping in metal‐nitrogen‐carbon single‐atom catalysts (SACs) is considered a powerful strategy to promote the electrocatalytic CO 2 reduction reaction (CO 2 RR), but the origin of enhanced catalytic activity is still elusive. Here, we disclose that sulfur doping induces an obvious proton‐feeding effect for CO 2 RR. The model SAC catalyst with sulfur doping in the second‐shell of FeN 4 (Fe 1 −NSC) was verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Fe 1 −NSC exhibits superior CO 2 RR performance compared to sulfur‐free FeN 4 and most reported Fe‐based SACs, with a maximum CO Faradaic efficiency of 98.6 % and turnover frequency of 1197 h −1 . Kinetic analysis and in situ characterizations confirm that sulfur doping accelerates H 2 O activation and feeds sufficient protons for promoting CO 2 conversion to *COOH, which is also corroborated by the theoretical results. This work deepens the understanding of the CO 2 RR mechanism based on SAC catalysts.

Abstract Electrochemical production of hydrogen peroxide (H 2 O 2 ) through two‐electron (2 e − ) oxygen reduction reaction (ORR) is an on‐site and clean route. Oxygen‐doped carbon materials with high ORR activity and H 2 O 2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen‐doped carbon nanosheet (OCNS 900 ) catalyst for 2 e − ORR. The OCNS 900 exhibits outstanding 2 e − ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g −1 at 0.75 V (vs. RHE) and H 2 O 2 production rate of 770 mmol g −1 h −1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C−OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e − ORR, which were corroborated by theoretical calculations.

Abstract The rational design of effective catalysts for sluggish oxygen evolution reactions (OERs) is desired but challenging. Nickel‐iron (NiFe) (oxy)hydroxides are promising pre‐electrocatalysts for alkaline OER. However, OER performances are limited by the slow reconstruction process to generate active species of high‐valance NiFe oxyhydroxides. In this work, a sulfate ion (SO 4 2− ) modulated strategy is developed to boost the OER activity of NiFe (oxy)hydroxide by accelerating the electrochemical reconstruction of pre‐catalyst and stabilizing the reaction intermediate of OOH* during OER. The SO 4 2− decorated NiFe (oxy)hydroxide catalyst (NF‐S0.15) is fabricated via scalable anodization of NiFe foam in a thiourea‐dissolved electrolyte. The experimental and theoretical investigations demonstrate the dual effect of SO 4 2− on improving OER performances. SO 4 2− leaching is favorable for the electrochemical reconstruction to form active NiFeOOH under OER condition. Simultaneously, the residual SO 4 2− adsorbed on surface can stabilize the intermediate of OOH*, and thus enhance the OER performances. As expected, NF‐S0.15 delivers an ultralow overpotential of 234 mV to reach the current density of 50 mA cm −2 , a fast OER kinetics (27.7 mV dec −1 ), and a high stability for more than 100 h. This unique insights into anionic modification could inspire the development of advanced electrocatalysts for efficient OER.