Layered Double Hydroxides and their Derived Nanomaterials for Efficient Electrochemical Water Splitting

Abstract

The electrochemical water splitting is an efficient and environment-friendly path-way to produce hydrogen which is a clean fuel. This PhD dissertation presents a comprehensive exploration of novel electrocatalytic materials tailored for efficient water splitting. The study focuses on the synthesis, characterization, and evaluation of three distinct materials, each demonstrating remarkable electrocatalytic properties for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes. The first type of material is based upon deposition of bimetallic (CoMn) layered double hydroxide (LDH) over the surface of highly crystalline copper oxide to form a composite material, CoMn-LDH@CuO/Cu2O. One electrocatalyst out of this class of materials exhibits remarkable OER performance, necessitating only an additional 297 mV potential to achieve a catalytic current density of 10 mA/cm2, with a minimal Tafel slope of 89 mV/dec. The synergistic interaction of CoMn-LDH and CuO/Cu2O contributes to an increased electrochemical active surface area (ECSA), enabling efficient OER processes with least charge transfer resistance (Rct). The second type of material, NiCo-alloy@CeO2, introduces a bifunctional electrode catalyst with superior performance for both OER and HER in alkaline environments. The integration of bimetallic (NiCo) alloy with cerium oxide (CeO2) nanorods leads toward significantly reduced overpotential of 170 mV at 20 mA/cm2 for OER and 221 mV for HER. The synergistic interface between alloy and CeO2, oxygen vacancies in CeO2 facilitate the ionic conductivity, are the main factors which are thought to uplift the water splitting efficiency. The third type of materials composed of bimetallic (NiFe) selenide which were derived from their parent LDH and supported over cobalt containing N-doped carbon nanomaterials (CoOx-NCNTs). The optimized electrocatalyst (NiFeSe@CoOx-NCNTs ) exhibits exceptional performance towards OER and HER under alkaline electrolyte conditions. Notably, it achieves a small overpotential of 240 mV at 20 mA/cm2 for OER, a reduced Tafel slope of 59.2 mV/dec. For HER, it attains 20 mA/cm2 at just 145 mV overpotential, exhibiting a small Tafel slope of 169 mV/dec. The catalyst also demonstrates a small Rct, a large ECSA, and exceptional stability over a continuous 15 h experimental period. The exceptional efficiency of NiFeSe@CoOx-NCNTs in both reactions holds significant promise for designing efficient water electrolyzer. Collectively, this thesis underscores the significance of tailored electrocatalytic materials in advancing the realm of renewable energy conversion. This research paves the way for future investigations into optimizing synthesis processes, uncovering underlying mechanisms, and broadening the applications of electrocatalysts, thus contributing to the ongoing global efforts to achieve a more sustainable energy future.