The critical effect of different additive interlayer anions on NiFe-LDH for direct seawater splitting: A theoretical study

Direct seawater electrolysis greatly alleviates the shortage of freshwater resources, emerging as a promising approach for hydrogen production. Unfortunately, the slow kinetics of oxygen evolution reaction (OER) and the complex seawater environment, especially the chloride oxidation reaction (ClOR), pose significant challenges for the design of direct seawater electrolysis catalysts. For the sake of enhancing corrosion resistance to chloride ions (Cl⁻), an alkaline environment is settled for increasing the potential difference between OER and competitive ClOR. NiFe-LDH has been recognized as a benchmark catalyst in alkaline environment owing to its unique advantages. However, in strongly alkaline environment, the deposition of Mg(OH)₂ and Ca(OH)₂ at the cathode limits the overall efficiency of direct seawater electrolysis. In this study, we have investigated the underlying effect of four different interlayer anions (PO₄³⁻, SO₄²⁻, CO₃²⁻, and NO₃⁻) on the OER activity, selectivity, and pH application range of NiFe-LDH using density functional theory. Furthermore, we have explored the intrinsic correlations between electronic structure and catalytic performance. Our results confirm that the interlayer anions play a favorable role in promoting OER activity. Among them, NiFe-LDH with PO₄³⁻ remarkably outperforms the other interlayer anions in terms of OER activity and selectivity, reducing the OER overpotential (η) to 0.29 V and overcoming the limitations associated with high pH conditions. Most importantly, there is a linear relationship between η and the charge transferred from the interlayer anion to the catalyst surface (ΔQ_tot), implying that the interlayer anions are able to regulate the catalytic activity through essential charge transfer. This study provides theoretical insights into the design and development of advanced OER catalysts that can simultaneously suppress ClOR for direct seawater electrolysis.