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Low-temperature etching of ZIF-67 is proposed for ultra-small cobalt/cobalt-oxide nanoparticles in nitrogen-doped graphene-networks as an efficient electrocatalyst for the oxygen reduction reaction.

The design of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable for water splitting. Here, Cedoped CoP was prepared through synthesizing a Ce-ZIF-67 precursor coupled with a phosphorization process. The introduction of Ce into CoP can lead to electronic modulation of Co, thus lowering the energy barrier for both to deliver better activity. The CoP with an optimized Ce-doping level exhibits high HER and OER performance and can be used as a highly efficient catalyst for water splitting. Here, Ce doping can introduce electronic modulation, optimizing the adsorption of H on CoP to promote HER performance as well as reduce the energy barrier of the potential-limiting step by facilitating electron transfer from Ce to Co. This work provides new insights into the development of a high-performance water-splitting electrocatalyst.

Nickel-based hydroxide hierarchical nanoarrays (NiyM(OH)x HNAs M = Fe or Zn) are doped with non-noble transition metals to create nanostructures and regulate their activities for the oxygen evolution reaction. Catalytic performance in these materials depends on their chemical composition and the presence of nanostructures. These novel hierarchical nanostructures contain small secondary nanosheets that are grown on the primary nanowire arrays, providing a higher surface area and more efficient mass transport for electrochemical reactions. The activities of the NiyM(OH)x HNAs for the oxygen evolution reaction (OER) followed the order of Ni2.2Fe(OH)x > Ni(OH)2 > Ni2.1Zn(OH)x, and these trends are supported by density functional theory (DFT) calculations. The Fe-doped nickel hydroxide hierarchical nanoarrays (Ni2.2Fe(OH)x HNAs), which had an appropriate elemental composition and hierarchical nanostructures, achieve the lowest onset overpotential of 234 mV and the smallest Tafel slope of 64.3 mV dec−1. The specific activity, which is normalized to the Brunauer–Emmett–Teller (BET) surface area of the catalyst, of the Ni2.2Fe(OH)x HNAs is 1.15 mA cm−2BET at an overpotential of 350 mV. This is ~4-times higher than that of Ni(OH)2. These values are also superior to those of a commercial IrOx electrocatalyst.