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Water splitting is an efficient strategy to produce purity hydrogen and convert intermittent electricity from renewable wind and solar sources. In this work, dense NiMoO4 micro-pillars arrays (MPAs) were in-situ grown on nickel foam (NF) through facile hydrothermal method, then the NiMoO4/NF were converted into NiMoO4–P/NF and NiFe/NiMoO4/NF via phosphating and electrodeposition method, respectively. The NiMoO4–P/NF electrode required small overpotentials of 34 mV@10 mA cm−2 and 130 mV@100 mA cm−2 for hydrogen evolution reaction (HER). The NiFe/NiMoO4/NF electrode exhibited excellent oxygen evolution reaction (OER) activity with overpotentials of 210 mV@10 mA cm−2 and 300 mV@100 mA cm−2. The overall water splitting using the anode-cathode couple of NiFe/NiMoO4/NF||NiMoO4–P/NF only consumes low voltages of 1.47 V@10 mA cm−2 for 100 h and 1.66 V@100 mA cm−2 for 50 h in 1 M KOH. The electronic modification and the well-designed hierarchical structure contribute the high energy-efficient and stabile overall water splitting.

Degradation of NO3− into harmless N2 is a significant challenge in the field of water treatment. In this work, 3D self-supported hierarchical electrode composed of ultra-thin Cu nanosheets-assembled micro-columns on porous nickel foam (Cu NSs/NF) was prepared by three steps, including electrodeposition of CuCl-Cu, thermal oxidation into CuCl-CuO and electrochemical reduction into Cu NSs. Benefitting from the advantages of large surface area and highly active interface as well as fast electron-transfer path, Cu NSs/NF exhibits the significant positive-shift of potential and higher current density than other Cu-based electrodes in the electrochemical reduction of NO3− (NO3−-ER). Not only that, an extremely high sensitivity of nitrate reduction response up to 11.23 mA mM−1 cm−2 was obtained by chronoamperometric test, which is much higher than those of previously reported works. Moreover, a conversion percentage of 99.7% for NO3−-ER was achieved on Cu NSs/NF cathode in NO3−-ER experiments. Finally, through the cathodic reduction of NO3− coupled with the anodic oxidation of Cl−, and the subsequent chemical reaction of NH4+ and ClO−, the highly efficient degradation of NO3− into N2 with selectivity as high as 97.2% was realized. This work provides a highly efficient Cu NSs/NF electrode and a promising way for degradation of NO3− into N2.

Hydrogen-motivated electrolysis of Na2CO3 for energy-saving production of NaOH and CO2/NaHCO3 is realized by the hydrogen oxidation reaction to insert proton into anolyte and the hydrogen evolution reaction to extract proton out of catholyte. Electrolytic voltage at 100 mA cm−2 is as low as 0.88 V; this voltage is only 35% of the voltage used in the traditional electrolysis.