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Layered double hydroxides (LDHs) with di-/trivalent metal cations are considered as one of the most promising materials for highperformance 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) 4 Fe(III) 1 hydroxide nanocones (NCs) with both features of α-type mixed octahedral(O h )/tetrahedral(T d ) coordination and LDH-analogous mixed di-/trivalences, i.e., mix-O h /T d LDH. Specifically, Co(II) 4 Fe(III) 1 hydroxide NCs in such a mix-O h /T d 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) 4 Fe(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-O h /T d 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.

A nonprecious electrocatalyst with high efficiency in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is extremely crucial for the development of high-performing metal–air batteries. In this work, a nonprecious-metal bifunctional catalyst of ultrafine and uniform Ni2.25Co0.75N nanoparticles anchoring on N-doped reduced graphene oxide (denoted as Ni2.25Co0.75N/NrGO) was prepared by the thermal ammonolysis of the corresponding hydroxide/graphene oxide precursor. As a result of the intimate combination of redox-active metal nitrides and electroconductive N-doped reduced graphene oxide (NrGO), the Ni2.25Co0.75N/NrGO hybrid not only exhibited high OER activity but also showed outstanding ORR kinetics and durability, comparable to commercial RuO2 and Pt/C electrocatalysts, respectively. Furthermore, Zn–air batteries assembled by using the as-prepared Ni2.25Co0.75N/NrGO hybrid electrocatalysts yielded a high power density and gravimetric energy density of 193 mW cm–2 and 864 W h kg–1, respectively, characteristic with a low charge/discharge voltage gap of 0.72 V and excellent cyclability up to 166 h at 10 mA cm–2 in an aqueous system. More importantly, the ORR experiment and X-ray photoelectron spectroscopy coupled with density functional theory calculations verified that the electronic transfer from bimetallic NiCo nitride to NrGO may enhance the ability in forming O2 adsorption and *OOH on NrGO, which is the possible origination of the ORR high activity.

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