Application Research Of Transition-metal Compounds/Nano Carbon Composites In Electro-catalyzing Oxygen Evolution

The growing global energy demand, coupled with the depletion of fossil fuels and the related negative environmental impact, is prompting intense research into the pursuit and utilization of various types of clean and sustainable energy conversion and storage technologies with high effciency, low cost, and environmental benignity. Electricity-driven water splitting to produce hydrogen fuels and oxygen is believed to be one of the most promising and appealing strategies to achieve the conversion of electric energy into chemical energy. OER was considered as the rate-controlled step of overall water splitting due to generating one oxygen molecule by adding large overpotential. To date, some precious metals and their oxides are recognized to be the best OER electrocatalysts since their lowest overpotential for the OER. However, their widespread applications are restricted signifcantly because of their high cost and low abundance. Therefore the development of low cost, stable and effective OER electrocatalyst is urgently required in order to facilitate the reaction.In order to overcome these difficulties, extensive efforts have been devoted to research of alternative OER electrocatalysts based on transition-metal elements (Such as Co, Ni and Fe) that are low cost,highly active, and stable long-term under oxidizing conditions. In this report we expand development of transition-metal compounds. The main points are as shown below:(1) In this section, hydrophilic and porous Cobalt Sulfide/CNT(CNT-CoS2) was synthesized by synchronous electrochemical deposition and dissolution. The structure of the CNT-CoS2 was characterized through SEM?TEM?STEM and XPS. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) measurements confirm the formation of hydrophilic groups (e.g., SO42-andSO32-) on the surface of the porous CoS2 during electrochemical oxidation. In this work, the as-prepared CNT-CoS2 composites exhibit a superior OER catalytic activity; the polarization curve and over-potential of catalyst after 1000 cycles overlays almost exactly with the initial sweep and 10,000s, with negligible changes of cathodic current and over-potential, suggesting the catalyst is highly stable and can withstand accelerated degradation.(2) Nickel and Iron binary hydroxides compounds/CNTs(NiFeOHx/CNTs) were synthesized by a typical constant potentials deposition. In this work, the as-prepared NiFeOHx/CNTs composites exhibit a superior OER catalytic activity both in 0.1 M and 1M KOH. The over-potential of catalyst after 12 hours, with negligible changes of cathodic current and over-potential, suggesting the catalyst is highly stable and can withstand accelerated degradation. The comprehensive performance of the NiFeOHx/CNTs electrocatalyst is comparable to or better than that of the same type OER catalyst. After analyzing the fitted EIS dates, the as-prepared possessed of ability of faster surface charge transfer and higher reaction rate. After incorporation of Fe into the structure of NiFeOHx/CNTs, The constant phase element (CPE) value of FeOHx/CNTs was larger than NiOHx/CNTs and NiFeOHx/CNTs, which indicated that catalytic activity of NiFeOHx/CNTs was enhanced.