Layered Double Hydroxides Based Nanocomposites And Its Electrocatalytic Performance On Bifunctional Oxygen Electrodes

Due to the continued deterioration of the climate and depletions of fossil, developing and exploring new clear energy become an vital scientific topic. Among the processes of energy conversation and storage, oxygen electrode reactions, which include ORR and OER, restrict the development of fuel cells and water electrolysis. Therefore people are constantly looking for high-performance oxygen electrode modified materials.LDH is a layered bi-metal hydroxides with tunable bi-metal, exchangble anion and memory effect. In this paper, we synthesized different LDH based nano-composites by in-situ growth, recovery-after-calcined and electrostatic assembly based on the properties of LDH. Then we investigated their bifunctional oxygen electrocatalytic performances. The main content list in the follow:1. Under hydrothermal conditions, NiFe-LDH grew along the GO films by giving suitable alkali and metal ions, then reduced GO. The as-prepared rGO-LDH shows lots of sphere-like cells which GO enhances its conductivity. The rGO-LDH modified electrode shows a OER onset overpotential of only 240 mV which is close to the RuO2, the current density increases to 32.388 mA/cm2 when 1.530 V. It also shows a ORR onset potential of 0.796 V, the limiting diffusion current density is about-3.845 mA/cm2. In methanol mixed solution, its current density decreases less than 10 %.2. Under reductive conditions, C3N4 nanosheets were assembled onto the GO-LDH. The sphere-like NG-LDH composites show a much larger surface area and a good conductivity due to the structure defects of N-doping and rGO. The NG-LDH modified electrode shows a OER onset overpotential of 256 mV, more 16 mV than non-N-doped rGO-LDH, but when 1.530 V its current density increases 9 times from NiFe-LDH to 42.636 m A/cm2. It shows a ORR onset potential of 0.853 V, half-wave potential of 0.802 V, which is superior to the tranditional layered materials. In methanol mixed solution, its current density decreases less than 8 %.3. The calcined products of CoFe-LDH was dissolved in GO solution, then doped N under a reductive conditions. The as-prepared NG/LDH is composed of irregularly hexagonal plates and N-doped reducted GO films which cause lots of structure defects to increaces specific surface area and ORR activity, the rGO enhences the conductivity of composite. The NG/LDH modified electrode shows a OER onset overpotential of 244 mV, when 1.53 V its current density increases 7 times from CoFe-LDH to 14.371 mA/cm2. It shows a ORR limiting diffusion current density of-5.222 mA/cm2, which is close to 20 wt% Pt/C. In methanol mixed solution, its current density is almost unchanged.4. NiFe-LDH nanosheets and GO nanosheets were auto-assembled in formamide by electrostatic attraction, the as-prepared GO-ELDH further modified by NH2-ILs, which named as IL-GR-ELDH. The NH2-ILs can enhence its conductivity and hydrophilic performance. The IL-GR-ELDH modified electrode shows a OER onset overpotential of ~282 mV, when 1.53 V current density increases 5 times from NiFe-LDH to 5.998 mA/cm2. It shows a ORR onset potential of 0.742 V, half-wave potential of 0.661 V. And its current density decreases less than 0.08% in methanol mixed solution.