Ni–O₄ as Active Sites for Efficient Oxygen Evolution Reaction with Electronic Metal–Support Interactions

Abstract

Precise adjustment of the metal site structure in single-atom catalysts (SACs) plays a key role in addressing the oxygen evolution reaction (OER). Herein, we report the synthesis of O-doped Ni SACs anchored on porous graphene-like carbon (Ni–O–G) using molten salts (ZnCl2 and NaCl) as templates, in which the unique Ni–O4 structure serves as the active sites. Ni–O–G, with an overpotential of only 238 mV (@ 10 mA cm–2), is one of the more advanced catalysts. An array of characterizations and density functional theory calculations show that the Ni–O4 coordination enables Ni to be closer to the Fermi level compared to traditional Ni–N4, enhancing the electronic metal–support interaction to facilitate OER kinetics. Thus, this work offers an alternative strategy for the structural modulation of Ni SACs and the effect of different coordination elements with the same atomic coordination structure on the intrinsic OER activity.

Catalytic oxidation mechanism of ethyl acetate on O-ligand-single-atom-Ni/2-dimensional reduced graphene oxide: the essential role of the O ligand

“…37 The four C atoms of the graphene are replaced by O atoms to simulate O doping and a Ni atom is positioned on the O-doped graphene (Ni–O 4 ) to model the SANi 5 -O-2DRGO. 31 The O atoms are sp 2 hybridized and form three coordinated covalent bonds with surrounding atoms. 38 The four O atoms are replaced by N atoms (Ni–N 4 ) to build SANi 5 -N-2DRGO.…”

“…Moreover, the images of HAADF-STEM and the surface sweep energy dispersive spectroscopy (EDS) of the SANi 5 -O-2DRGO catalyst show a highly dispersive single Ni atom (Fig.1c-f).The atomic dispersion state and bonding conguration of Ni in SANi 5 -O-2DRGO are further investigated by the normalized Ni K-edge X-ray absorption ne structure (XAFS) and Fouriertransformed EXAFS (FT-EXAFS). The position of the Ni K-edge is related to the Ni valence state 31. As shown in Fig.2a,the Ni K-edge of SANi 5 -O-2DRGO lies between that of Ni foil and NiO, indicating the valence state of Ni in SANi 5 -O-2DRGO is between 0 and +2.…”

“…[27][28][29][30] Cao et al discovered that O ligands are more electronegative than N ligands and can better regulate the electron transfer between charge carriers and metals. 31 In this paper, O-ligand-single-atom-Ni/2D graphene materials (SANi X -O-2DRGO) are prepared for the catalytic oxidation of VOCs including ethyl acetate, n-hexane, and toluene. The catalytic properties of these VOCs were studied, and their reusability, water resistance and stability were explored.…”

“…45Based on the above results, the SANi 5 -O-2DRGO model was constructed (Fig.2c). The position of the d-band center (3 d ) relative to the Fermi level is an important surface parameter that determines the reactivity of the metal surface 31. As depicted in the partial density of states (PDOS) of the Ni in Fig.2d, the 3 d value of SANi 5 -O-2DRGO is −1.34 eV, which is closer to the Fermi level than the conventional SANi 5 -N-2DRGO (−1.79 eV).…”

The regulatory function of the d-orbital structure in TM@g-t-C4N3 for bifunctional catalysis of the oxygen evolution/reduction reaction

“…15,16 Single-atom catalysts (SACs) have been considered to have broad prospects in catalysis owing to the maximized utilization of loaded metal atoms and the excellent catalytic activity. 17,18 Numerous studies have revealed the commendable catalytic ability of SACs for a series of reactions, such as the OER, [19][20][21] ORR, [22][23][24] hydrogen evolution reaction (HER), [25][26][27][28] nitrogen reduction reaction (NRR), 29,30 carbon dioxide reduction reaction (CO 2 RR), 31,32 etc. In order to acquire a SAC structure with sufficiently dispersed transition metal (TM) atoms, a suitable substrate is firstly required, which should restrain the aggregation of loaded TM atoms.…”