A facile approach to tailor electrocatalytic properties of MnO2 through tuning phase transition, surface morphology and band structure

[Display omitted] •A facile hydrothermal approach is reported to control the phase transition of MnO2.•The in-situ growth of MnO2 on NF has a hybrid nanowires-nanosheets morphology.•Rich Mn3+ and O vacancies, and well band-alignment tunability has been achieved.•The α-MnO2 with combined merits exhibits superior electrocatalytic performance. The structural and electronic properties of MnO2 based electrocatalysts are key factors determining their electrochemical performance. To date, it is still challenging to synergistically tune the crystal structure, morphology, and electronic band (i.e., band gap and band alignments) of MnO2 through facile synthesis approaches. This study has reported a one-step hydrothermal method to synthesize a prototypical MnO2 electrocatalyst with optimized structural and electrochemical properties. By simply adjusting the hydrothermal time, the phase transition from polymorphic δ to α can be induced in MnO2. The obtained nanowires on nanosheets structure grown in-situ on nickel foam provides a large surface area, great accessible active sites, and good mass/charge transfer efficiency. Further investigation through first-principles calculations reveals that compared to δ-MnO2, the α-MnO2 polymorph with rich oxygen vacancies has better band-alignment tunability, which is also beneficial for improving the electrochemical performance. The α phase MnO2 exhibits superior catalytic performance for both OER and HER (OER overpotential of 0.45 V at 50 mA cm−2 and HER overpotential of 0.14 V at 50 mA cm−2). The developed synthesis method can be extended to catalyst designs that require precise control of phase and morphology evolution in a wide range of applications.