Achieving degradation and conversion of targeted contaminant s and simultaneous ly obtaining energy is an effective way to solve environmental problems and energy crises. Hydrogen is a clean, environmentally friendly,non polluting and renewable energy carri er. High enthalpy contaminants possess the characteristics of easy oxidation and low conversion potential. T he substitution of contaminant degradation in wastewater for the water splitting not only achieves effective purification of wastewater , but also produces green hydrogen energy. How to improve the conversion and degradation efficiency of the electrode and develop a highly efficient and energy saving electrochemical apparatus is a key issue to solve the popularization and application of el ectrocatalytic technology. Therefore, taking nitrogenous pollutants as an example, this paper studies the preparation of inexpensive high activity cathode/anode material electrodes and the development of high efficiency wastewater purification reactors, an d f ocus on the migration,transformation and degradation process of nitrogenous contaminants at the electrode water phase interface and the efficiency and mechanism of electrocatalytic hydrogen evolution
(1) A polycrystalline molybdenum carbide (Mo 2 C) electrode was prepared via hydrothermal calcination method and applied to the mechanism research of hydrogen evolution . The synthesis process of polycrystalline molybdenum carbide found that tuning additive (tungsten) context could realize the transform ation of molybdenum carbide from α phase to β phase. Thermogravimetry differentialscanning calorimetry (TG DSC) indicate ed that the increasing the amount of tungsten to elevate the temperature required for Mo C bond formation was a critical factor affecti ng the phase transformation of molybdenum carbide . Benefiting from the optimal Mo C bond length s , large surface area and abundant active sites, the polycrystalline molybdenum carbide electrode with optimal tungsten addition exhibited excellent electrocatal ytic activity and stability in the HER Compared with pure α Mo 2 C and β Mo 2 C, the polycrystalline molybdenum carbide electrode only required an overpotential of 148 and 93 mV to drive the current density of 20 mAcm 2 in 0.5 M H 2 SO 4 and 1.0 M KOH electrolyte, respectively.
(2)C obalt oxide CoO nanowire electrode s with OVs are prepared via incorporation of B using a facile pyrolysis strategy and applied to the mechanism research of oxygen evolution Density functional theory (DFT) c alculations predict ed that the incorporation of boron (B) facilitates the generation of oxygen vacancies ( in the transition metal oxide. X ray photoelectron spectroscopy, Raman spectroscopy and electron paramagnetic resonance spectroscopy confirmed th e presence of oxygen vacancies. X ray absorption spectroscopy (XANES) of the near edge structure further found that oxygen vacancies in CoO were mainly derived from the disordering of the local structure caused by B doping. DFT calculation results further reveal ed that the oxidation of *OOH was the rate limiting step for OVs enriched CoO in the OER and that the presence of OVs could effciently lower the reaction barrier for breaking Co O bond, contributing to the improvement of OER kinetics. As expected, the OVs enriched CoO exhibits a low overpotential of 280 mV to reach the current density of 10 mA cm 2 under basic conditions.
(3)In view of the sluggish kinetics and high reaction potential of oxygen evoluiton in the decompositon of water , t he oxidative degradation of high enthalpy containtants in wastewater is employed to replac e the traditional water oxidation .Furthermore, a conti nuous flow reactor with high efficiency hydrogen production and simultaneous contaminants degradation is developed . High resolution transmission electron microscopy (HRTEM) show ed that the active species on the surface of nickel phosphide were in situ generated during the degradation process of pollutants. Based on X ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy, we confirmed that the formation of the desired oxidation state of Ni IIIaccounted for the efficient urea degradation. The scenario was beneficial for accelerating charge transfer across the interface between the anode and electrolyte,thereby achieving synchronous degradation of pollutants and generation of energy hydrogen at low voltage , whereby a continuous flow reactor was constructed. A voltage of only 1. 5 0 V supported currents of 31.3 and 6. 5 mA in urea containing or not solutions, respectively, which reached 150 and 35 mA after the voltage was increased to 1.70 V, several times higher than that under basic conditions. After the discharge of 578 C, the removal efficiency for urea degradation reached 79.6%.
(4)Using the principle of battery charge and discharge, the cobalt phosphide electrode is used as a charge and discharge mediator to effectively separate the cathode hydrogen evolution and anode pollutant degradation reaction in the electrolytic cell in time, thereby achieving the efficacy of persistent charg e hydrogen evolution and rapid discharge decontamination and the purpose of membrane free separation of H 2 . Based on this, a high efficiency membrane free hydrogen separation and contaminant degradation electrolyzer apparat us was developed In the
electrolytic cell device, the high capacitance of the CoP NAs mediator supported persistent H 2 seperation , where the H 2 production period achieved 1500 s at acurrent density of 10 mA cm 2 , almost 3.1 times longer than that for pure CoP (480s).Alternatively, the energy stored in the mediator could be exhausted via coupling with the oxidation of ammonia with NiSe as the anode . a total driving voltage of 1.55 V was required to support a current density of 10 mA cm 2 in the ammonia containing solution, ~0.14 V lower than that under basic conditions