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

Electrocatalyticoverall water splitting is a promising approachfor hydrogen production, and the rational design of the catalyst onthe atomic level is critical for decreasing the energy barrier inboth hydrogen and oxygen evolution reactions (HER/OER). Herein, wereport an NiIr single atom alloy loaded NiFe-LDH (NiIr<INF>SAA</INF>-NiFe-LDH) and Ir single atom loaded NiFe-LDH (Ir<INF>SAC</INF>-NiFe-LDH)for overall water splitting. The Ir single atoms are found via EXAFSfitting and DFT calculations to be located on the top of Fe3+ with Ir-O<INF>6</INF> coordination on Ir<INF>SAC</INF>-NiFe-LDH.The as-prepared NiIr<INF>SAA</INF>-NiFe-LDH presents an overpotentialof 28.5 mV at 10 mA cm-2 in the HER and Ir<INF>SAC</INF>-NiFe-LDH exhibits an overpotential of 194 mV at 10 mA cm-2 in the OER, respectively. Moreover, the electrolyzerassembled by NiIr<INF>SAA</INF>-NiFe-LDH and Ir<INF>SAC</INF>-NiFe-LDHpresents 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 perkilogram of H<INF>2</INF>, meeting the target raised by the US Departmentof Energy (<US $2 kg<INF>H<INF>2</INF> </INF> -1). Such high HER activity for NiIr<INF>SAA</INF>-NiFe-LDH can beattributed to the strong electronic interaction between Ni and Irsingle atoms in NiIr<INF>SAA</INF>, resulting in an optimized hydrogenadsorption energy (& UDelta;G <INF>H</INF>* = -0.17eV). And the Ir single atoms modify the electronic structures of theadjacent Ni2+ in NiFe-LDH, which reduces the energy barrierof the O<INF>2</INF> emission, thus enhancing the OER performance.