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Graphical abstract Abstract Here, a series of porous carbon based supercapacitor electrode materials have been synthesized by means of pyrolysis and hydrothermal methods combining with KOH activation using the biomass wastes mung bean husks as resources. The influence of synthesis process on the morphology, structure and supercapacitor performance of mung bean husks derived porous carbons has been investigated systematically. Especially, it is found that these oxygen-containing groups on the biochar play a crucial role in fabricating the three-dimensional (3D) hierarchical porous structure carbon. The original bio-structured porous carbon (PC 3-600), the 3D architecture porous carbon (HPC 2-700) and the porous carbon block (HPPC 2-700) have a high specific surface area, and the former mainly contains micropores and the latter two possess multistage pores. The specific capacitance of PC 3-600 , HPC 2-700 and HPPC 2-700 is respectively up to 390 F g−1, 353 F g−1, 304 F g−1 at 1 A g−1, and still maintains as high as 287 F g−1, 270 F g−1 and 235 F g−1 with corresponding retention ratio of 73.5%, 76.48%, 77.3% even at a high current density of 50 A g−1. HPC 2-700 //HPC 2-700 symmetric supercapacitor achieves a high energy density of 20.4 Wh kg−1 at 872 W kg−1 in 1 M Na 2 SO 4 electrolyte. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-efficiency and functional NiO/CeO 2 heterostructure nanocatalyst exhibits outstanding HER performance in 1 M KOH with a low overpotential of 99 mV at the current density of 10 mA•cm−2 and a modest Tafel slope of 78.4 mV dec−1. • The atomic-scale analysis of the interfacial structure and the locale electronic states have been provided by the combination of advanced electron microscopic characterization and first principle calculation. • It has been found that the charge transfer occurs from Ni to Ce at the interfacial region, resulting in the valence state variation and increased formation of V O and Ce3+ cations, which would optimize the ΔG H* and facilitate the hydrogen evolution process. • The improved HER performance could be attributed to synergistic coupling interactions and electron redistribution at the interface of NiO and CeO 2. To understand the underlying mechanism of the interfacial charge transfer and local chemical state variation in the nonprecious-based hydrogen evolution reaction (HER) electrocatalysts, a model system of the NiO/CeO 2 heterostructure was chosen for investigation using a combination of the advanced electron microscopic characterization and first-principles calculations. The results directly proved that interfacial charge transfer occurs from Ni to Ce, leading to reduction in the valence state of Ce and increased formation of V O. This would optimize ΔG H* and facilitate the hydrogen evolution process, resulting in outstanding HER performance in 1 M KOH with a low overpotential of 99 mV at the current density of 10 mA•cm−2 and a modest Tafel slope of 78.4 mV•dec−1 for the NiO/CeO 2 heterostructure sample. Therefore, the improved HER performance could be attributed to the synergistic coupling interactions and electron redistribution at the interface of NiO and CeO 2. These results concretely demonstrate the direct determination of the interfacial structure of the heterostructure and provide atomistic insights to unravel the underlying mechanism of interfacial charge transfer induced HER performance improvement. [ABSTRACT FROM AUTHOR]