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This work develops CoNi alloys with slight oxidation@N,O co-doped carbon (NOC) as multifunctional catalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and Zn–air batteries. Their outer NOC shells have direct contributions to ORR, OER and HER activity that is dominated by N and O dopants that closely correlate with active adjacent C atoms. Meanwhile, the inner cores (CoNi alloys with slight oxidation) can provide indirect and important contributions. Relying on enhanced collective contributions of outer NOC shells and inner cores that are tuned by Co/Ni molar ratios, CoNi(1 : 1)-TB-800N2 with a Co/Ni molar ratio of 1 : 1 affords optimized multifunctional activity. Furthermore, it also brings about optimal Zn–air battery performance: ∼98.6% and ∼74.8% of theoretical specific capacity and energy density, respectively, and more than 100 h of stable charge–discharge operation at high current densities. [ABSTRACT FROM AUTHOR]

Developing earth-abundant highly efficient catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is indispensable for the widespread implementation of electrochemical water splitting to store renewable energy. Herein, amorphous bimetallic selenide (Ni–Fe–Se) hollow nanospheres electrodeposited on nickel foam (Ni–Fe–Se/NF) are developed as a bifunctional catalyst for the HER and OER. The HER and OER bifunctional activity of Ni–Fe–Se/NF outperforms those of monometallic Ni–Se/NF and Fe–Se/NF owing to the synergy of Ni and Fe in Ni–Fe–Se/NF. Moreover, the amorphous hollow spherical morphology of Ni–Fe–Se/NF increases the active site density and facilitates the mass transfer of electrolytes and H2/O2 products. Ni–Fe–Se/NF drives a current density of 10 mA cm−2 with an overpotential of ∼85 mV for the HER and 100 mA cm−2 with an overpotential of ∼222 mV for the OER. As the HER and OER bifunctional catalyst, Ni–Fe–Se/NF can split alkaline water with total voltages of ∼1.52 V and ∼1.66 V at 10 mA cm−2 and 100 mA cm−2, respectively, and remain stable over 50 hours of operation in 1 M KOH. [ABSTRACT FROM AUTHOR]

Non-precious bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in regenerative fuel cells and rechargeable metal–air batteries. In this contribution, less active CeO2 is introduced for regulating the ORR/OER bifunctional activity of Co3O4@N-doped carbon (NC). The introduced CeO2 plays essential roles in increasing the surface contents of Co2+, Co3+ and N species in CeO2/Co3O4@NC for ORR/OER processes, while still maintaining hierarchical porosity and large specific surface area. Furthermore, the surface acid–base properties for the adsorption of oxygen molecules (for the ORR) and activation of water molecules (for the OER) and the charge transfer efficiency are also improved by the introduced CeO2. As a result, significantly enhanced ORR/OER bifunctional activity is achieved for the optimal and desired electrocatalyst, i.e., CeO2/Co3O4@NC. Its bifunctional activity is comparable or even superior to that of the benchmarked 20 wt% Pt/C (for the ORR) and IrO2 (for the OER), respectively. In the applications of Zn–air batteries, the battery with CeO2/Co3O4@NC still exhibits higher performance than the battery with mixed 20 wt% Pt/C + IrO2, due to its outstanding bifunctional activity toward the ORR and OER. [ABSTRACT FROM AUTHOR]

An ε-MnO2/metal–organic-framework (Fe) (i.e., ε-MnO2/MOF(Fe)) composite was synthesised by integrating ε-MnO2 and a MOF(Fe) support. The composite was characterised using X-ray diffraction, N2 adsorption–desorption, field emission scanning electron microscopy, transmission electron microscopy, elemental mapping, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The ORR activity of the composite was evaluated by cyclic and linear sweep voltammetries in an alkaline electrolyte. The results revealed that in the ε-MnO2/MOF(Fe) composite, ε-MnO2 is in the form of nanorods, each with one end protruding and the other firmly anchored on the MOF(Fe) matrix with a high porosity and a high specific surface area. This unique structure of the composite is advantageous for oxygen diffusion and contact with ε-MnO2 during reactions, resulting in much better ORR activity and stability than those of ε-MnO2 in an alkaline electrolyte. The ε-MnO2/MOF(Fe)-catalysed ORR favours an apparent 4-electron transfer pathway in which oxygen was first reduced to hydroperoxide, which was further chemically decomposed into primarily OH− and O2. [ABSTRACT FROM AUTHOR]

Developing earth-abundant highly efficient catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is indispensable for the widespread implementation of electrochemical water splitting to store renewable energy. Herein, amorphous bimetallic selenide (Ni-Fe-Se) hollow nanospheres electrodeposited on nickel foam (Ni-Fe-Se/NF) are developed as a bifunctional catalyst for the HER and OER. The HER and OER bifunctional activity of Ni-Fe-Se/NF outperforms those of monometallic Ni-Se/NF and Fe-Se/NF owing to the synergy of Ni and Fe in Ni-Fe-Se/NF. Moreover, the amorphous hollow spherical morphology of Ni-Fe-Se/NF increases the active site density and facilitates the mass transfer of electrolytes and H 2 /O 2 products. Ni-Fe-Se/NF drives a current density of 10 mA cm -2 with an overpotential of ∼85 mV for the HER and 100 mA cm -2 with an overpotential of ∼222 mV for the OER. As the HER and OER bifunctional catalyst, Ni-Fe-Se/NF can split alkaline water with total voltages of ∼1.52 V and ∼1.66 V at 10 mA cm -2 and 100 mA cm -2 , respectively, and remain stable over 50 hours of operation in 1 M KOH.