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CoIr@CN is successfully synthesized from Ir-doped 2D Co-MOF. CoIr@CN exhibits a low overpotential of 269 mV/70 mV in 1.0 M KOH for OER/HER and 25 mV in 0.5 M H2SO4 for HER at 10 mA cm−2 due to the optimized carbonation process induced by Ir doping.

The sluggish kinetics and four electron oxidation process of the oxygen evolution reaction (OER) limit the widespread application of electrochemical water splitting. Recently, NiFe-layered double hydroxide (NiFe LDH) has shown great potential to boost the OER process. However, limited active sites and poor conductivity severely hinder the further improvement of the OER performance. Herein, oxygen vacancy-rich hierarchical NiFe LDH (v-NiFe LDH) microtubes assembled from two dimensional (2D) nanosheets were synthesized via a template-assisted strategy. The plentiful oxygen vacancies (VO) could efficiently promote the intrinsic conductivity of the obtained LDH. Meanwhile, featuring hierarchical microtubes and 2D nanosheets, the as-prepared electrocatalyst exhibits abundant catalytically active sites and excellent structural stability. Benefitting from the defect and morphological engineering, the OER activity of v-NiFe LDH has obviously enhanced, with an ultralow overpotential of 195 mV at 10 mA cm−2 and a low Tafel slope of 47.9 mV dec−1, as well as long-term stability at 10 mA cm−2. In addition, theoretical calculations further elucidate that the Fe site is the primary active site in v-NiFe LDH and VO can enhance the conductivity and accelerate the OER kinetic process through decreasing the bandgap of NiFe LDH and reaction energy of the rate-determining step.

Water splitting by electrolysis is a promising technology that can address rising energy demands and environmental pollution. However, the oxygen evolution reaction (OER), as one half-cell reaction of water splitting, always suffers from slow kinetics and a large overpotential due to the four proton-coupled electron transfer process, and dominates the overall process efficiency. IrO2 is a promising and widely used catalyst for the OER in commercial applications. Herein, we obtained low-crystalline nano-IrO2 particles confined in an amorphous Ir-based MOF (IrO2@Ir-MOF) through a simple solvothermal reaction, in which ultrafine IrO2 particles are uniformly distributed in the Ir-MOF skeleton. The fabricated IrO2@Ir-MOF-ppy electrode exhibits excellent OER activity with an overpotential of 207 mV, to achieve a current density of 10 mA cm−2 in 1 M KOH solution, outperforming most previously reported OER catalysts. The IrO2@Ir-MOF‖IrO2@Ir-MOF couple exhibits promising activity and stability for the overall water splitting reaction in 1 M KOH (1.53 V).

The low electronic conductivity of sulfur and the diffusion and shuttle of polysulfide intermediates are the main obstacles of the cathode that restrain the progress of lithium–sulfur (Li–S) batteries. To address the two main predicaments, we explored a dual functional 3D hierarchical filter element structured Mo2C nanosheet based sulfur electrode. The Mo2C based sulfur electrodes fulfill the requirements of conductivity (30 S cm−1) and entrapment of diffusing polysulfide intermediates, and meanwhile possess the advantages of high crystallinity and large specific surface area. As a filter and reservoir for polysulfides, Mo2C nanosheets possess a strong chemical interaction with polysulfides to mitigate the shuttling of polysulfides. The dual functional Mo2C nanosheet based electrode exhibited a high initial discharge capacity of ca. 1200 mA h g−1 and ca. 800 mA h g−1 after 300 cycles at 0.2C. Moreover, the flexibility of the sulfur electrode is explored through an in situ fabrication on carbon cloth in a soft-package configuration.

Uniform nitrogen-doped C/Ni/TiO2 hollow spindles were successfully prepared with Ni nanoparticles encapsulated into the hollow N-doped TiO2/C matrix. This intriguing architecture not only exhibits favorable conductivity, but also provides a large quantity of accessible active sites for lithium ion insertion, thus contributing to superior lithium storage properties.

Ni–Co sulfides are considered as promising electrode materials for electrochemical pseudocapacitors because of their rich redox chemistry and great structural flexibility with low cost. However, traditional Ni–Co sulfides still suffer from poor electrochemical performance due to relatively low electronic conductivity and structural instability. Herein, we present facile syntheses of hollow Ni–Co sulfide nanoboxes with tunable compositions, i.e., NiCo2S4 and Ni2CoS4, by using a low-temperature wet-chemical method. The resultant Ni–Co sulfides demonstrate high specific capacitances with enhanced cycling stability and rate capability. The NiCo2S4 electrode exhibits a capacitance of 1588 F g−1 at 2 A g−1 and a capacitance retention of 88.2% at 5 A g−1 after 4000 cycles, while the Ni2CoS4 electrode exhibits a capacitance of 1200 F g−1 at 2 A g−1 and a capacitance retention of 90.5% at 5 A g−1 after 4000 cycles. All the experimental results illustrate nanostructured Ni–Co sulfides to be promising electrode materials for high-performance supercapacitors.