Synthesis of Co(II)-Fe(III) Hydroxide Nanocones with Mixed Octahedral/Tetrahedral Coordination toward Efficient Electrocatalysis

Layered double hydroxides (LDHs) with di-/trivalent metal cations are considered as one of the most promising materials for high-performance electrocatalysts. On the other hand, α-type hydroxides, with cations in controllable mixed octahedral/tetrahedral coordination, have been rarely investigated. Here, we report a general approach to prepare novel Co(II)4Fe(III)1 hydroxide nanocones (NCs) with both features of α-type mixed octahedral(Oh)/tetrahedral(Td) coordination and LDH-analogous mixed di-/trivalences, i.e., mix-Oh/Td LDH. Specifically, Co(II)4Fe(III)1 hydroxide NCs in such a mix-Oh/Td LDH structure were synthesized and tested as electrocatalysts for the oxygen evolution reaction (OER) and were found to be capable of delivering a current density of 10 mA cm–2 at a low overpotential of ∼263 mV, with a remarkable turnover frequency (TOF) that is 1 order of magnitude higher than that of Co(II)4Fe(III)1 LDH nanoplatelets with octahedral coordination only. It was also found that the NCs exhibited a very high electrochemical active surface area (ECSA) due to their hollow conical morphology and large interlayer spacing. More importantly, spectroscopic characterizations of the samples after the electrochemical reaction, associated with density functional theory (DFT) calculations, proved that mix-Oh/Td LDH NCs are more likely to form oxyhydroxides with cobalt and iron toward higher oxidation states. As a result, the ability to adsorb oxygen free radicals may be significantly enhanced and the energy barrier of OER is substantially lowered.