No abstract

Nickel‐iron based hydroxides have been proven to be excellent oxygen evolution reaction (OER) electrocatalysts, whereas they are inactive toward hydrogen evolution reaction (HER), which severely limits their large‐scale applications in electrochemical water splitting. Herein, a heterostructure consisted of NiFeV hydroxide and iron oxide supported on iron foam (NiFeV@FeOx/IF) has been designed as a highly efficient bifunctional (OER and HER) electrocatalyst. The V doping and intimate contact between NiFeV hydroxide and FeOx not only improve the entire electrical conductivity of the catalyst but also afford more high‐valence Ni which serves as active sites for OER. Meanwhile, the introduction of V and FeOx reduces the electron density on lattice oxygen, which greatly facilitates desorption of Hads. All of these endow the NiFeV@FeOx/IF with exceptionally low overpotentials of 218 and 105 mV to achieve a current density of 100 mA cm−2 for OER and HER, respectively. More impressively, the electrolyzer requires an ultra‐low cell voltage of 1.57 V to achieve 100 mA cm−2 and displays superior electrochemical stability for 180 h, which outperforms commercial RuO2||Pt/C and most of the representative catalysts reported to date. This work provides a unique route for developing high‐efficiency electrocatalyst for overall water splitting.

Transition metal nitrides are promising electrocatalysts for hydrogen evolution reaction (HER) owing to their Pt-like electronic structure. However, the harsh nitriding conditions greatly limit their large-scale applications. Herein, ultrafine Co3Mo3N-Mo2C (<1 nm)-decorated carbon nanofibers (Co3Mo3N-Mo2C/CNFs) were prepared by electrostatic spinning followed by pyrolysis treatment, in which the MoCo-MOF simultaneously serves as the precursor and nitrogen source. The generated synergistic interactions between Mo2C and Co3Mo3N significantly adjust the electronic structure of Mo2C and afford a fast charge transfer, which endows the resultant hybrid with superior HER electrocatalytic performances. Specifically, the as-obtained Co3Mo3N-Mo2C/CNF delivers a low overpotential of only 76 mV to achieve a current density of 10 mA cm–2 and superior durability with no obvious degradation for 200 h in acidic media. This performance outperforms most of the transition metal-based electrocatalysts reported to date. This work paves a new way for the design of catalysts with ultrasmall size and high efficiency in energy conversion.

The successful preparation of a perovskite-based heterostructure is important for broadening the applications of perovskites in the field of electrocatalysis, especially in a hydrogen evolution reaction (HER). Nevertheless, the limited active sites of perovskites severely hindered the HER properties. Herein, an in situ exsolution method was used to construct a nanocomposite based on V-doped BaCoO 3−δ decorated with Ba 3 (VO 4 ) 2 (BVCO19) for alkaline HER. The exsolved Ba 3 (VO 4 ) 2 can induce more Co 4+ ions on BaCoO 3−δ , which serves as active sites for the release of H 2 . Meanwhile, by regulating the valency of V and Co species, the catalyst can reach a charge balance by generating more oxygen vacancies, which greatly facilitates the adsorption and dissociation of H 2 O molecules. The synergistic effect between the oxygen vacancies and high-valence Co 4+ leads to an enhanced HER performance of BVCO19. The as-obtained catalyst delivers a low overpotential of 194 mV at 10 mA cm −2 as well as impressive stability for 100 h in alkaline media, which outperforms pristine BaCoO 3−δ and most of the nonprecious-based perovskite oxides. This work provides new insights into the preparation of perovskite-based heterostructure for boosting HER.