Driving the electrocatalytic hydrogen evolution reaction (HER) with solar-energy cells is considered a green and sustainable way to produce H 2 . Herein, CoO-Mo 2 N hollow heterojunctions were designed for effective HER based on the combined virtues of the hollow structure and heterojunctions. The hollow CoMoO 4 -Co(OH) 2 precursor was first synthesized via the reaction of Co 2+ from ZIF-67 with MoO 4 2− and OH − in a Na 2 MoO 4 solution. A series of experiments indicate the formation of the hollow Co-Mo-O precursor followed a mechanism analogous to the nanoscale "Kirkendall Effect". After heating in NH 3 , the CoO-Mo 2 N hollow heterostructure was obtained. The Mo species in the precursor played an important role in maintaining the morphology under nitridation treatment. The hollow structure is favorable for contact and diffusion of electrolyte with (in) catalysts, while the CoO in CoO-Mo 2 N is favorable for the dissociation of water. Both promote the HER. Under optimized conditions, the hollow catalyst exhibited good HER performance with an overpotential of 65 mV at 10 mA cm −2 in 1 M KOH. The performance is better than that of many nonprecious metal-based catalysts. An electrolyzer composed of CoO-Mo 2 N heterojunctions as the cathode and NiFe-LDH as the anode can be driven by a solar cell to achieve effective overall water splitting. The adjudication of MOFs makes the route promising for the design of robust catalysts for advanced application.

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The design of the electrode with high-area and mass capacitance is important for the practical application of supercapacitors. Here, we fabricated the porous NiCoP nanowalls supported by Ni foam (NiCo-P/NF) for supercapacitors with win-win high-area and mass capacitance. The NiCoOH nanowall precursor was prepared by controlling the deposition rate of Ni 2+ and Co 2+ on NF through a sodium acetate-assisted (floride-free) process. After the phosphorization, the NiCo-P nanowalls formed with high loading about 8.6 mg cm −2 on NF. The electrode combined several advantages favorable for energy storage: the plentiful pores beneficial for ion transport, the nanowalls for easy accommodation of electrolyte, good conductivity of NiCo-P for easy transport of electrons. As expected, the NiCo-P/NF exhibited a high specific mass capacitance (1,861 F g −1 at 1 A g −1 , 1,070 F g −1 at 10 A g −1 ), and high area capacitance (17.31 F cm −2 at 5 mA cm −2 and 10 F cm −2 at 100 mA cm −2 ). The asymmetric supercapacitor (ASC) composed of NiCo-P/ NF positive electrode coupled with commercial active carbon negative electrode exhibited a high energy density of 44.9 W h kg −1 at a power density of 750 W kg −1 . The ASC can easily drive fans, electronic watch and LED lamps, implying their potential for the practical application.

A novel “precursor-transformation” route was developed for the high-yield synthesis of tube-like ZIF-8 (with around 0.6 g of ZIF-8/60 mL of solvent, the yield is over 90% based on Zn). The advantages of high yield, easy synthesis and a special tube-like morphology are largely favourable for the application of ZIF-8 based materials.