Boosting Oxygen Reduction of Single Iron Active Sites via Geometric and Electronic Engineering: Nitrogen and Phosphorus Dual Coordination

Abstract

Atomically dispersed transition metal active sites have emerged as one of the most important fields of study because they display promising performance in catalysis and have the potential to serve as ideal models for fundamental understanding. However, both the preparation and determination of such active sites remain a challenge. The structural engineering of carbon-and nitrogencoordinated metal sites (M−N−C, M = Fe, Co, Ni, Mn, Cu, etc.) via employing new heteroatoms, e.g., P and S, remains challenging. In this study, carbon nanosheets embedded with nitrogen and phosphorus dual-coordinated iron active sites (denoted as Fe-N/P-C) were developed and determined using cutting edge techniques. Both experimental and theoretical results suggested that the N and P dual-coordinated iron sites were favorable for oxygen intermediate adsorption/desorption, resulting in accelerated reaction kinetics and promising catalytic oxygen reduction activity. This work not only provides efficient way to prepare well-defined single-atom active sites to boost catalytic performance but also paves the way to identify the dual-coordinated single metal atom sites.

Understanding and Optimizing Ultra‐Thin Coordination Polymer Derivatives with High Oxygen Evolution Performance

“…The Ni K ‐edge XANES spectra of the Ni 10−x Fe x ‐CPs show a characteristic pre‐edge feature around 8335 eV corresponding to the ideal square‐planar geometry of NiM 4 (M: heteroatom). [ 39–42 ] The Ni K ‐edge extended X‐ray absorption fine structure (EXAFS) spectra were recorded to quantify the coordination environment of Ni atoms in Ni 10−x Fe x ‐CPs. The Fourier‐transform FT‐EXAFS spectrum of Ni 5 Fe 5 ‐CPs (Figure S23b, Supporting Information) displays two prominent peaks, one peak at 1.35 Å associated to the Ni‐C coordination shell, and another peak at 2.42 Å arising from the Ni‐N coordination shell, which underscores the square‐planar geometry of the Ni atoms in Ni 5 Fe 5 ‐CPs.…”

“…The Fourier‐transform FT‐EXAFS spectrum of Ni 5 Fe 5 ‐CPs (Figure S23b, Supporting Information) displays two prominent peaks, one peak at 1.35 Å associated to the Ni‐C coordination shell, and another peak at 2.42 Å arising from the Ni‐N coordination shell, which underscores the square‐planar geometry of the Ni atoms in Ni 5 Fe 5 ‐CPs. [ 39–42 ] The FT‐EXAFS spectrum of Ni‐CPs (Figure S23b, Supporting Information) shows three peaks in the range of 1–3 Å. The first one at 1.17 Å corresponds to Ni‐C/N pairs, the second one at 1.78 Å arises from the NiO bond, and the third one at 2.39 Å is mainly due to the Ni‐N/C pairs.…”

“…As illustrated in Figure S35, Supporting Information, the deconvoluted high‐resolution XPS spectrum of N 1s in NiFe‐CPs showed two peaks, one at 399.32 eV and another one at 401.12 eV, which were assigned to NC and NNi/Fe bonds. [ 39–41,49a,b,50 ] The deconvoluted high‐resolution Ni 2p XPS spectrum of NiFe‐CPs displayed two pairs of peaks located at 856.72 and 872.42 eV, 858.32 and 875.62 eV, respectively, attributed to the NiO and NiC bonds. [ 45,51,52 ] FeO bonds are evident from the high‐resolution Fe 2p spectrum shown in Figure S35c, Supporting Information.…”

Recent Advances in Phosphorus‐Coordinated Transition Metal Single‐Atom Catalysts for Oxygen Reduction Reaction

“…With the addition of nitrogen, M−N x P y sites have more configurations than M−P x sites. The configurations of M−N x P y can be classified into three groups based on the relative positions of N and P: (1) both N and P in the basal plane of graphene; [15,26] (2) both N and P at the edge position; [24] and (3) N in the graphene plane while P as an additional ligand as shown in Figure 2 [25] . All the three groups of M−N x P y sites are thermodynamically stable.…”

“…In the past few years, theoretical and experimental studies have been carried out on the phosphorus coordination active sites, including phosphorus‐coordinated metal (M−P x ) [10–12,19–22] and nitrogen‐phosphorus dual‐coordinated metal (M−N x P y ) [15,23–26] . These catalysts have shown superiority in activity in comparison with N‐coordinated ones.…”