Single‐Atom Doping and High‐Valence State for Synergistic Enhancement of NiO Electrocatalytic Water Oxidation

Abstract

The NiO‐based electrocatalytic oxygen evolution reaction (OER) of water splitting is recognized as a promising approach to produce clean H2 fuel. However, the OER performance is still low, and especially, the overpotential is larger than 200 mV at the current density of 10 mA cm−2. Herein, an Ir@IrNiO sample is prepared with single‐atom (SA) Ir4+ doping and surface metallic Ir nanoparticles loaded onto the NiO. Owing to the bonding of the loaded Ir with surface‐exposed Ni2+, the nearby Ni atoms exist in the +3 valence state, that is, the surface‐loaded Ir particles behave like a stabilizer for the Ni3+ sites. Under the synergistic effect of SA Ir4+ and high‐valance‐state Ni3+, the Ir@IrNiO nanostructure effectively reduces the overpotential to 195 mV at a current density of 10 mA cm−2. Moreover, it gives an Ir‐content‐normalized current density of 0.0457 A mgIr−1, 72.1 times higher than that of the best commercialized IrO2 (6.33 × 10−4 A mgIr−1), under the condition of 1.5 V versus reversible hydrogen electrode. Operando Raman and X‐ray absorption fine‐structure (XAFS) measurements reveal that there are more surface‐active species of Ni3+, which adsorb and activate water molecules to form Ni3+–*OH at low voltage, the intermediate of Ni4+–•O is then formed at a relatively high bias voltage, and then the •O is transferred to the SA Ir4+ sites to generate Ir4+–O–O with OH at increased voltage. This work can help design more SA‐based highly active OER materials.

Ru doping boosts electrocatalytic water splitting

“…Electronic structure engineering has a significant influence on the electrochemical properties of catalysts and is widely regarded as a promising strategy for tailoring the catalytic capability. 54,55 Heteroatom doping is a highly efficient avenue to modify the electronic structure of catalysts, which can induce slight atomic arrangement distortions, 56 redistribute…”

“…Electronic structure engineering has a significant influence on the electrochemical properties of catalysts and is widely regarded as a promising strategy for tailoring the catalytic capability. 54,55 Heteroatom doping is a highly efficient avenue to modify the electronic structure of catalysts, which can induce slight atomic arrangement distortions, 56 redistribute the charge density, 57 and stimulate more active sites, 58 consequently leading to the substantial improvement in electrocatalytic performance. Moreover, electronic structure modulation is also demonstrated to be highly efficient for accelerating electron transfer from the electrode to reactants for promoting reaction kinetics.…”

Ultrasmall Ir nanoclusters on MnO2 nanorods for pH-universal oxygen evolution reactions and rechargeable zinc–air batteries

“…Sustainable Energy & Fuels electrocatalytic processes of all the samples. 67 The inset shows the simulated equivalent circuit and the tting parameters are summarized in Table S2. † The x%-Ir-MnO 2 samples have a much smaller charge transfer resistance (R ct ) than IrO 2 , and as anticipated, 5%-Ir-MnO 2 has the smallest value in the series.…”

Electronic and architecture engineering of hammer-shaped Ir–NiMoO4-ZIF for effective oxygen evolution

“…26–28 Owing to its high intrinsic activity and appropriate binding energy with oxygen-involved intermediates, Ir has been considered an ideal dopant for modifying the electronic properties of a catalyst. 29,30 For one thing, ultralow Ir doping not only modulates the local electronic configuration of the initial catalyst, but also serves as additional active sites to further promote the OER performance. For another thing, the introduction of an ultralow amount of Ir can also preserve the structural features of the original materials.…”