Iron Coordination Polymer, Fe(oxalate)(H2O)2 Nanorods Grown on Nickel Foam via One-Step Electrodeposition as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

Abstract

Iron coordination polymer, Fe(ox)(H2O)2 (H2ox = oxalic acid) nanorods were grown on a nickel foam (NF) collector via a one-step electrodeposition method, which can be directly used as a freestanding and binder-free electrode for efficient oxygen evolution reaction (OER) electrocatalysis. The optimum sample, Fe(ox)(H2O)2/NF-(-1.4)-15, was obtained at an electrodeposition potential of -1.4 V vs Ag/AgCl for 15 min, which can deliver OER current densities of 40 and 100 mA cm-2 at overpotentials of 270 and 340 mV, respectively. The sample also exhibits good long-term OER activity during 80 h electrolysis at 20 mA cm-2, which is superior to those of previously reported metal-organic framework (MOF) catalysts. Furthermore, the formation mechanism of the Fe(ox)(H2O)2 nanorods is primarily investigated and the effect of the species of metal ions in MOF on the morphology and OER behavior is also explored. In addition, density functional theory (DFT) calculations reveal that the rate-limiting steps on Fe(ox)(H2O)2 and Ni(ox)(H2O)2 are the formation of Fe*-OOH and Ni*-OH intermediates with maximum ΔG values of 1.628 and 1.710 eV, respectively, which is attributed to the different electronic configurations of Ni and Fe, thus giving rise to different d-band centers and different affinities for adsorbates.