While the past years have witnessed great achievement in pseudocapacitors, the inauguration of electrode materials of high-performance still remains a formidable challenge. Moreover, the capacity and rate capability of the electrode depends largely on its electrical conductivity, which ensures fast charge transfer kinetics in both the grain bulk and grain boundaries. Here, nickel hydroxides with oxygen vacancies are facilely fabricated via a hydrothermal method. The active materials exhibit a high specific capacitance of 3250 F·g⁻¹ and a high areal of capacitance of 14.98 F·cm⁻² at 4.6 mA·cm⁻². The asymmetric supercapacitor device based on our material delivers a high energy density of ~ 71.6 Wh·kg⁻¹ and a power density of ~ 17,300 W·kg⁻¹ and could retain ~ 95% of their initial capacitance even after 30,000 cycles. In addition, the defect-rich hydroxides demonstrate higher electrical conductivity as well as dielectric constant, which is responsible for the superior pseudocapacitive performance. Our new scientific strategy in terms of taking the advantages of oxygen vacancies might open up new opportunities for qualified pseudocapacitive materials of overall high performances not only for nickel hydroxides but also for other metal hydroxides/oxides.

High electrical conductivity guarantees a rapid electron transfer and thus plays an important role in electrocatalysis. In particular, for the single atom catalysts (SACs), to facilitate interaction between the single atom and supports, precisely engineering the conductivity represents a promising strategy to design SACs with high electrochemical efficiency. Here we show rhodium (Rh) SAC anchored on Co₃O₄ nanosheets arrays on nickel foam (NF), which is modified by a facile phosphorus (P-doped Rh SAC-Co₃O₄/NF), possessing an appropriate electronic structure and high conductivity for electrocatalytic reaction. With the introduction of P atom in the lattice, the electrocatalyst demonstrates outstanding alkaline oxygen evolution reaction (OER) activity with 50 mA·cm⁻² under overpotential of 268 mV, 6 times higher than that of Ir/C/NF. More interestingly, the P-doped Rh SAC-Co₃O₄/NF can get 50 mA·cm⁻² at only 1.77 V for overall water splitting. Both electrical conductivity studies and density functional theory (DFT) calculations reveal that the high conductivity at grain boundary improves the charge transfer efficiency of the Rh catalytic center. Furthermore, other noble-metal (Ir, Pd, and Ru) doped Co₃O₄ nanosheets arrays are prepared to exhibit the general efficacy of the phosphorus doping strategy.