Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN 4 site usually exhibits an unsatisfactory ORR activity due to its poor O 2 adsorption and activation. Here, we report an axial Fe-O coordination induced electronic localization strategy to improve its O 2 adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe-O coordination evokes the electronic localization among the axial direction of O-FeN 4 sites to enhance O 2 adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe-O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O 2 adsorption and activation with an ultralow Tafel slope of 27.5 mV dec −1 and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.

Developing high-performance electrocatalysts toward hydrogen evolution reaction is important for clean and sustainable hydrogen energy, yet still challenging. Herein, we report a single-atom strategy to construct excellent metal-organic frameworks (MOFs) hydrogen evolution reaction electrocatalyst (NiRu0.13-BDC) by introducing atomically dispersed Ru. Significantly, the obtained NiRu0.13-BDC exhibits outstanding hydrogen evolution activity in all pH, especially with a low overpotential of 36 mV at a current density of 10 mA cm−2 in 1 M phosphate buffered saline solution, which is comparable to commercial Pt/C. X-ray absorption fine structures and the density functional theory calculations reveal that introducing Ru single-atom can modulate electronic structure of metal center in the MOF, leading to the optimization of binding strength for H2O and H*, and the enhancement of HER performance. This work establishes single-atom strategy as an efficient approach to modulate electronic structure of MOFs for catalyst design.

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-N4 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-N4 site ORR activity as examples, we demonstrate that the hybridization between Fe 3dz2, 3dyz (3dxz) and O2 π* orbitals is the origin of Fe-N4 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 *O2 as descriptors can accurately predict the ORR activity of Fe-N4 site. Furthermore, these descriptors and ORR activity of Fe-N4 site are mainly distributed in two regions with obvious difference, which greatly relate to the height of Fe 3d projected orbital in the Z direction. This work provides a new insight into the ORR activity of single-atom M-N-C catalysts.

Electrochemical production of hydrogen peroxide (H 2 O 2 )t hrough two-electron (2 e À )o xygen reduction reaction (ORR) is an on-site and clean route.O xygen-doped carbon materials with high ORR activity and H 2 O 2 selectivity have been considered as the promising catalysts,h owever,t here is still alackofdirect experimental evidence to identify true active sites at the complex carbon surface.H erein, we propose ac hemicalt itration strategy to decipher the oxygen-doped carbon nanosheet (OCNS 900 )c atalyst for 2e À ORR. The OCNS 900 exhibits outstanding 2e À ORR performances with onset potential of 0.825 V( vs.R HE), mass activity of 14.5 Ag À1 at 0.75 V( vs.R HE) and H 2 O 2 production rate of 770 mmol g À1 h À1 in flow cell, surpassing most reported carbon catalysts.Through selective chemical titration of C = O, C À OH, and COOH groups,wefound that C = Ospecies contributed to the most electrocatalytic activity and were the most active sites for 2e À ORR, which were corroborated by theoretical calculations.

Atomically dispersed FeN 4 catalysts have been considered as potential materials to replace Pt-based catalysts for the oxygen reduction reaction (ORR), but they often suffer from sluggish O 2 activation kinetics due to the symmetrical charge distribution. Herein, we introduce external N, including pyrrolic-N (PN) and graphitic-N (GN), as an electron acceptor near FeN 4 to regulate its charge distribution and improve its ORR activity. Theoretical calculations reveal that introduction of PN evokes much enhanced electron redistribution and local electrical field on the Fe site compared with those observed with GN introduction and the pristine one. Synchrotron X-ray absorption spectroscopy and X-ray photoelectron spectroscopy validate the positive charge accumulation of Fe in the FeN 4 site induced by introducing PN. Thus, the obtained FeN 4 -PN exhibits a great performance for ORR in 0.1 M KOH with a remarkable half-wave potential of 0.91 V versus reversible hydrogen electrode, as well as a Tafel slope of 58 mV decade −1 . This work provides a guide to improve the catalytic performances of single-atom catalysts by introducing chargeredistribution sites.