Atomic Modulation of Single Dispersed Ir Species on Self-Supported NiFe Layered Double Hydroxides for Efficient Electrocatalytic Overall Water Splitting

Abstract

Electrocatalytic overall water splitting is a promising approach for hydrogen production, and the rational design of the catalyst on the atomic level is critical for decreasing the energy barrier in both hydrogen and oxygen evolution reactions (HER/OER). Herein, we report an NiIr single atom alloy loaded NiFe-LDH (NiIrSAA-NiFe-LDH) and Ir single atom loaded NiFe-LDH (IrSAC-NiFe-LDH) for overall water splitting. The Ir single atoms are found via EXAFS fitting and DFT calculations to be located on the top of Fe3+ with Ir–O6 coordination on IrSAC-NiFe-LDH. The as-prepared NiIrSAA-NiFe-LDH presents an overpotential of 28.5 mV at 10 mA cm–2 in the HER and IrSAC-NiFe-LDH exhibits an overpotential of 194 mV at 10 mA cm–2 in the OER, respectively. Moreover, the electrolyzer assembled by NiIrSAA-NiFe-LDH and IrSAC-NiFe-LDH presents a low cell voltage of 1.49 V at 10 mA cm–2 and a long-term stability of over 120 h at 200 mA cm–2 in overall water splitting with an estimated cost of US $1.12 per kilogram of H2, meeting the target raised by the US Department of Energy (<US $2 kgH2–1). Such high HER activity for NiIrSAA-NiFe-LDH can be attributed to the strong electronic interaction between Ni and Ir single atoms in NiIrSAA, resulting in an optimized hydrogen adsorption energy (ΔGH* = −0.17 eV). And the Ir single atoms modify the electronic structures of the adjacent Ni2+ in NiFe-LDH, which reduces the energy barrier of the O2 emission, thus enhancing the OER performance.