Growth of ultrathin nanosheets of nickel iron layered double hydroxide for the oxygen evolution reaction

Because of low cost and abundance, nickel-iron double layered hydroxide (NiFe LDH) is seen as a viable substitute for noble-metal-based electrodes for the oxygen evolution reaction (OER). Herein, we report the growth of NiFe LDH in the form of fine nanosheets in a single step using benzyl alcohol-mediated chemistry. The electrochemical studies clearly suggest that benzyl alcohol is capable of inducing effective chemical interaction between Ni and Fe in the NiFe LDH. The overpotential to produce benchmark 10 mA cm⁻² (η₁₀) for the NiFe LDH electrode is only ∼270 mV_RHE, which is much smaller than those of benchmark IrO₂ (η₁₀ = 318 mV_RHE), nickel hydroxide (η₁₀ = 370 mV_RHE) and iron hydroxide (η₁₀ = 410 mV_RHE) for the OER. The difference of the overpotential requirement increases further with increasing current density, indicating faster kinetics of the OER at the catalytic interface of the NiFe LDH. Estimation of Tafel values verifies this notion – the Tafel slopes of NiFe LDH, Ni(OH)₂, and FeOOH are calculated to be 48.6, 55.8, and 59.3 mV dec⁻¹, respectively. At η = 270 mV, the turnover frequency (TOF) of the NiFe LDH is 0.48 s⁻¹, which is ∼8 and ∼11 folds higher than those of Ni(OH)₂ (0.059 s⁻¹) and FeOOH (0.042 s⁻¹). In addition to Tafel and TOF, the NiFe LDH electrode has favorable electrochemically active surface area and electrochemical impedance. The electrochemical stability of the NiFe LDH electrode is assessed by conducting potentiostatic measurements at η = 270 mV_RHE (∼10 mA cm⁻²) and at η = 355 mV_RHE (∼30 mA cm⁻²) for 24 h of continuous oxygen production.