Ultrahigh-Loading of Ir Single Atoms on NiO Matrix to Dramatically Enhance Oxygen Evolution Reaction

Abstract

Engineering single-atom electrocatalysts with high-loading amount holds great promise in energy conversion and storage application. Herein, we report a facile and economical approach to achieve an unprecedented high loading of single Ir atoms, up to ∼18 wt %, on the nickel oxide (NiO) matrix as the electrocatalyst for oxygen evolution reaction (OER). It exhibits an overpotential of 215 mV at 10 mA cm −2 and a remarkable OER current density in alkaline electrolyte, surpassing NiO and IrO 2 by 57 times and 46 times at 1.49 V vs RHE, respectively. Systematic characterizations, including X-ray absorption spectroscopy and aberration-corrected Z-contrast imaging, demonstrate that the Ir atoms are atomically dispersed at the outermost surface of NiO and are stabilized by covalent Ir−O bonding, which induces the isolated Ir atoms to form a favorable ∼4+ oxidation state. Density functional theory calculations reveal that the substituted single Ir atom not only serves as the active site for OER but also activates the surface reactivity of NiO, which thus leads to the dramatically improved OER performance. This synthesis method of developing high-loading single-atom catalysts can be extended to other singleatom catalysts and paves the way for industrial applications of single-atom catalysts.

Recent Advances in Single-Atom Electrocatalysts for Oxygen Reduction Reaction

“…In very recent years, great progress has been made [104]. For example, the loading of isolated metal atoms has been as high as 18 wt% [105], the general method has been extended to synthesize SAECs for more than 34 types [102], and the production of SAECs on a kilogram scale has been realized [106]. Finally, the introduction of the deep learning algorithm together with big data technology will greatly speed up the screening process and start up a new direction of rational design and modification for complicated SAECs with expected electrochemical catalytic performance.…”

“…This approach could prepare a single-atom Ir catalyst with remarkably high Ir loading up to 14.8 wt% [ 109 ]. With carbon cloth- (CC-) supported NiO (NiO/CC) as the support, Wang et al prepared a single-atom Ir catalysts with the Ir loading as high as 18 wt% [ 105 ]. Firstly, a piece of NiO/CC was immersed into a chloroiridic acid ethanol solution for 10 min and then dried at 80°C.…”

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

“…Ir atom introducing excess electron to NiO, enhanced the activity of Ni toward the OER. [135] Apart from the adjacent metal atoms, nonmetal element can also be activated. The work presented by Lou and co-workers prepared isolated Ni atoms on hierarchical MoS 2 nanosheets supported on multichannel carbon matrix (MCM) nanofibers (named as MCM@MoS 2 -Ni).…”

“…The spheres in green, light brown, red, and pink denote the Ni, Ir, O, and H atoms, respectively. a-c) Reproduced with permission [135]. Copyright 2020, American Chemical Society.d) Calculated densities of states for MoS 2 -Ni and MoS 2 .…”

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives

“…Therein, the formed *OH species on Ni sites could easily relocate to the surrounding Ir sites to create a joint reaction pathway. 343 The discussion of the real active site in a catalytic support should consider both the electronic structure effects and multi-site reaction mechanisms. Current studies mainly rely on DFT calculations, and thus more experimental evidence based on recent advanced techniques, such as ATR-FTIR and operando XAS, as mentioned in Parts I and II, is required to unambiguously identify the active sites and their reaction mechanisms in future investigations.…”