To effectively enhance the energy density and overall performance of electrochemical capacitors (ECs), a new strategy is demonstrated to increase both the intrinsic activity of the reaction sites and their density. Herein, nickel cobalt phosphides (NiCoP) with high activity and nickel cobalt hydroxides (NiCo-OH) with good stability are purposely combined in a hierarchical cactus-like structure. The hierarchical electrode integrates the advantages of 1D nanospines for effective charge transport, 2D nanoflakes for mechanical stability, and 3D carbon cloth substrate for flexibility. The NiCoP/ NiCo-OH 3D electrode delivers a high specific capacitance of ≈1100 F g −1 , which is around seven times higher than that of bare NiCo-OH. It also possesses ≈90% capacitance retention after 1000 charge-discharge cycles. An asymmetric supercapacitor composed of NiCoP/NiCo-OH cathode and metal-organic framework-derived porous carbon anode achieves a specific capacitance of ≈100 F g −1 , high energy density of ≈34 Wh kg −1 , and excellent cycling stability. The cactus-like NiCoP/NiCo-OH 3D electrode presents a great potential for ECs and is promising for other functional applications such as catalysts and batteries.

Water electrolysis has been considered as one of the most efficient approaches to produce renewable energy, although efficient removal of gas bubbles during the process is still challenging, which has been proved to be critical and can further promote electrocatalytic water splitting. Herein, a novel strategy is developed to increase gas bubble escape rate for water splitting by using nonwoven stainless steel fabrics (NWSSFs) as the conductive substrate decorated with flakelike iron nickel-layered double hydroxide (FeNi LDH) nanostructures. The as-prepared FeNi LDH@NWSSF electrode shows a much faster escape rate of gas bubbles as compared to that of other commonly used three-dimensional porous catalytic electrodes, and the maximum dragging force for a bubble releasing between NWSSF channels is only one-seventh of the dragging force within nickel foam channels. As a result, it exhibits excellent electrocatalytic performance for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with low overpotentials of 210 and 110 mV at the current density of 10 mA cm in 1 M KOH for OER and HER, respectively. There is almost no current drop after a long-time durability test. In addition, its performance for full water splitting is superior to that of the previously reported catalysts, with a voltage of 1.56 V at current density of 10 mA cm.

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Hydrogen generation by electrocatalysis water splitting is considered as one of the most promising techniques to address the energy crisis and environmental pollution. Highly efficient, low-cost, and stable catalysts are crucial to speed sluggish kinetics of the hydrogen evolution reaction (HER). Molybdenum disulfide has been considered to be a promising substitute to Pt-based materials, but its inherently low conductivity, finite active edge sites due to the thermodynamically stable basal plane, and the self-stacking and agglomeration properties still impede the HER activity. In addition, optimization of the electrode structure is equally critical for industrial high-rate hydrogen production. Herein, on the basis of the system engineering concept, we report a manganese-doped MoS2 ultrathin nanosheet anchoring on a fin-tube-like hierarchical carbon skeleton vertically to achieve the synergistic optimization of intrinsic activity and electrode architecture. The superhydrophilic and superaerophobic electrode with conductive carbon nanoarray structure can accelerate the mass transport (gas bubbles and electrolyte) and electron transfer processes. In addition, theoretical calculation reveals that all the hydrogen adsorption free energies of basal planes, S-edge, and Mo-edge for doped MoS2 have decreased. Moreover, the electronic structure of the Mn-doped MoS2 monolayer shows the absence of band gap, indicating improved inherent conductivity. This finely crafted self-supported binder-free electrode with integrated architecture shows a low overpotential of 130 mV at −10 mA/cm2, a Tafel slope as low as 44 mV/dec, and excellent durability even at a high cathodic current density of 200 mA/cm2 in 0.5 M H2SO4. This system engineering optimizing strategy may pave the way for the design of commercially available electrocatalysts.

Transition metal oxides exhibit strong structure-property correlations, which has been extensively investigated and utilized for achieving efficient oxygen electrocatalysts. However, high-performance oxide-based electrocatalysts for hydrogen evolution are quite limited, and the mechanism still remains elusive. Here we demonstrate the strong correlations between the electronic structure and hydrogen electrocatalytic activity within a single oxide system Ti 2 O 3 . Taking advantage of the epitaxial stabilization, the polymorphism of Ti 2 O 3 is extended by stabilizing bulk-absent polymorphs in the film-form. Electronic reconstructions are realized in the bulk-absent Ti 2 O 3 polymorphs, which are further correlated to their electrocatalytic activity. We identify that smaller charge-transfer energy leads to a substantial enhancement in the electrocatalytic efficiency with stronger hybridization of Ti 3 d and O 2 p orbitals. Our study highlights the importance of the electronic structures on the hydrogen evolution activity of oxide electrocatalysts, and also provides a strategy to achieve efficient oxide-based hydrogen electrocatalysts by epitaxial stabilization of bulk-absent polymorphs.