Structure And Performance Study On The Ni-based Layered Hydroxides Electrocatalysts

Electrochemical water splitting has been regarded as an important approach for sustainable and renewable energy conversion and storage. However, the water splitting efficiency is greatly limited by the kinetically sluggish of multi-electron process of oxygen evolution reaction (OER), which requires highly active electrocatalysts to overcome the large overpotential. As is well known, noble metals oxides such as IrOx and RuOx have been widely considered as the active OER catalysts. Unfortunately, their scarcity and high cost significantly prevent further large-scale applications; therefore,it is highly imperative to seek low-cost and durable alternatives for efficient OER performance. Via using co-precipitation method, we have successfully synthesized Ni(OH)2 nanosheet and The Cr-doped Ni0.75Fe0.25(OH)2 25 hydrotalcite nanosheets. By introducing defects and electron delocalization, respectively, we boost our electrochemical water oxidation performance of Ni-based materials. The detail content of this dissertation are as follows:1. Electron delocalization boosting the catalytic activity of layered hydrotalcites for efficient electrochemical water oxidationDeveloping high-performance oxygen evolution reaction(OER) electrocatalysts is of great importance for sustainable and renewable energy conversion and storage. Here,via delocalizing the electron population around the active sites of layered hydrotalcites,we significantly facilitate the electron-donation from the active sites in Cr-dopedNi0.75Fe0.25(OH)2 25and greatly reduce the charge transfer barrier by an order of magnitude for high OER activity. The Cr-doped Ni0.75Fe0.25(OH)2 25 hydrotalcite nanosheets could thus achieve a small overpotential of 235mV at 10 mA/cm2 with an excellent Tafel slope of ～39mV/dec. The X-ray absorption near-edge spectra and theoretical calculations reveal that the strong overlap of d orbitals between Cr with unpaired d electrons and Ni ions promotes ～0.3 electron π-donation from Ni2+ to neighboring Cr (Fe) ions, and then evidently decreases the adsorption free energy of water molecule to -1.45eV for efficient OER performance.2. Nickle hydroxides for efficient electrochemical oxygen evolution reactionLow cost and high performance of oxygen evolution reaction electrocatalysts always are our target for their huge potential in energy store and clean energy. Via making Ni(OH)2 nanosheets which are small and gathering much defects, we successfully overcome the scaling-limit effects partly. The efficient electrochemical oxygen evolution reaction performance is owed to more surface active sites. In summary, we only used 285mV and 330mV to achieve a current density of 10 mA·cm2 in 1M KOH and 0.1M KOH, respectively. And Tafel slope of our Ni(OH)2 is also better than the commercial IrO2. Further more, our Ni(OH)2 nanosheets can stably operate in different alkaline condition and can constant working for more than 15 hours in 1M KOH.