Evaluating Fe-Site and Vacancy Dependent Intrinsic Activity of NiFe Layered Double Hydroxides through Cavity Microelectrodes

We report evaluating the intrinsic activity of Ni(OH) 2, NiFe layered double hydroxides (LDHs), and NiFe-LDH having vacancies for oxygen evolution reaction (OER) by the use of cavity microelectrodes (CMEs) with controllable mass loading. The number of active Ni sites ( N Ni-sites ) ranging from 1 × 10 12 to 6 × 10 12 is quantitatively correlated with OER current, which reveals that the introduction of Fe-sites and vacancies increases the turnover frequency (TOF) from 0.027 to 0.118 and 0.165 s –1, respectively. Electrochemical surface area (ECSA) is further quantitatively correlated with N Ni-sites, which indicates that N Ni-sites per unit ECSA ( N Ni-per-ECSA ) is decreased by the introduction of Fe-sites and vacancies. Therefore, the difference of OER current per unit ECSA ( J ECSA ) is reduced compared with that of TOF. The results demonstrate that CMEs provide a good platform to evaluate intrinsic activity with TOF, N Ni-per-ECSA, and J ECSA more reasonably.