The Synthesis And Catalytic Hydrogen Evolution Of CoP Nanomaterials

With the increasing of population and the development of economy, the energy imbalance issues are becoming prominent between demand and supply. The limited fossil fuel on earth has not been enough to maintain the human sustainable development. Moreover, long-term dependence on carbon based energy materials has led to many serious environmental and climate issues. Therefore, seeking renewable, clean and carbon-neutral alternative energy resources is urgently needed. Hydrogen can perfectly solve these problems between human and environment as a clean and renewable energy, and the traditional method of using fossil fuel to hydrogen production could not fundamentally solve the problem of energy shortage, so the key question is how to product mass hydrogen with low-cost, sustainable and pollution-free method. Recently, cobalt phosphide nanomaterials have been studied widely on catalytic hydrogen evolution for its low overpotential, good conductivity and high stability in acid or alkali. However, the preparation technology has the disadvantages of high cost and harsh reaction conditions, which needs further improvement. In addition, the role and mechanism of cobalt phosphate in the photocatalytic process need to be further clarified. Based on the above, we attempt to prepare a high hydrogen evolution activity of cobalt phosphide nanomaterials using low cost raw materials by a simple gas-solid phosphating reaction method. On the basis of this, the photocatalytic hydrogen production behavior of cadmium sulfide nanorods with cobalt phosphide was discussed. The research contents and the results of this paper were obtained as follows:(1) We carried on a systematic study on the preparation of CoP nanomaterials, and selected a low-cost and simple gas-solid phosphating reaction method to synthesize CoP nanomaterials. Using this method, by controlling the synthesis conditions of reaction temperature, reaction time, cobalt precursor and so on, realized the controllable preparation of cobalt phosphide nanomaterials. The cobalt phosphide nanocubes, nanosheets, nanorods and nanowires were synthetized with different morphology. Finally, a preliminary discussion on the principle of controllable preparation and the effect for catalytic reaction is carried out(2) The electrocatalytic hydrogen evolution behaviors of the prepared cobalt phosphate nanomaterials were nvestigated systematically. The morphology of cobalt phosphate nanomaterials was found to have great influence on the electrocatalytic activity of hydrogen evolution. Among the four kinds of nanomaterials, cobalt phosphide nanowires showed the highest electrocatalytic activity for hydrogen evolution, and the order was nanorods< nanosheets< nanocubes< nanowires. When the loading of cobalt phosphate nanowires on the electrode was 0.58 mg/cm2, the over potential was only 95.3 mV at 10 mA/cm2. This indicated that the prepared cobalt phosphate nanowires were likely to be widely used in the field of hydrogen production. In addition, the morphology had a great influence on the stability of cobalt phosphate nanomaterials. The stability of the nanosheets and nanocubes were good, while the nanowires and nanorods were not satisfactory. Therefore, in order to achieve the balance between the catalytic activity and stability of hydrogen evolution, the controlling of the morphology needs further study.(3) Using CoP nanomaterials as cocatalyst, CdS nanorods as photocatalyst, and lactic acid as sacrificial agent, we designed CoP/CdS nanocomposites through a simple deposition-precipitation method. We found that CoP/CdS nanocomposite was an efficient photocatalytic material, who could reach the optimum value of 106 mmol·g-1·h-1 for hydrogen evolution activity. In the progress of photocatalytic hydrogen evolution, the role of CoP was important for two aspects. Firstly, CoP could effectively enrich the electron generated from CdS to suppress the recombination of electron-hole pairs. Secondly, the lower hydrogen evolution potential of CoP was the center of hydrogen evolution. The hydrogen production on CoP nanoparticals were more effective than that of CdS nanorods. As an efficient cocatalyst for CdS, CoP is likely to be a promising alternative to Pt in the future practical application.