La/Ce doped CoFe layered double hydroxides (LDH) highly enhanced oxygen evolution performance of water splitting

Abstract

The design of a new, low-cost, high-efficiency and stable oxygen evolution reaction catalyst is of great significance to water electrolysis technology. In this paper, La-doped and Ce-doped CoFe LDH was prepared to enhance OER. Experiments show that the OER performance with 25%La-CoFe LDH and 25%Ce-CoFe LDH is better than CoFe LDH. And the oxygen evolution potential of 25%La-CoFe LDH at a current density of 10 mA/cm 2 is 1.547 V, which is far lower than CoFe LDH(1.694 V). And it also has lower Tafel slope(125 mV/dec), larger electrochemical specific surface area(2.46mF/cm 2 ) and lower charge transfer resistance(37.5 Ω). Through a series of characterization test analysis, it can be concluded that after La 3+ or Ce 3+ partially replaces Fe 3+ , the CoFe LDH system has more defects. This may be due to the fact that the ionic radius of La 3+ and Ce 3+ is much larger than that of Fe 3+ , and La 3+ and Ce 3+ have unique electronic structures. The partial replacement of Fe 3+ will affect the electronic structure of CoFe LDH, thereby enhancing the electronic coordination in the system, thereby exhibiting excellent OER performance. In this article, we use La 3+ and Ce 3+ doping to regulate CoFe LDH, and the results show that the introduction of La 3+ and Ce 3+ improves the performance of CoFe LDH's oxygen evolution reaction. Compared with CoFe LDH, 25%La-CoFe LDH and 25%Ce-CoFe LDH have lower oxygen evolution potential, smaller Tafel slope, smaller charge transfer resistance and larger electrochemical active area. Fig. 7 Explains the reason for the excellent electrocatalytic performance of 25%La-CoFe LDH and 25%Ce-CoFe LDH. The excellent OER properties of them are attributed to the following points: (1) La 3+ and Ce 3+ have special electronic structures. When entering the main layer of LDH, d -electron transitions occur. When Fe 3+ is partially replaced, there is a strong electron interaction with LDH, which promotes electron transfer in the OER process. In addition, because the ion radius of La 3+ and Ce 3+ is much larger than that of Fe 3+ , it will cause lattice defects and increase the electrochemical active surface area when entering LDH, thus showing efficient OER activity. (2) The introduction of La 3+ and Ce 3+ may affect the energy of the CoFe LDH system, causing the electron binding energy of Co 2+ to have a positive migration phenomenon, and this energy change may accelerate the electron transfer speed, thereby improving OER performance. In Summary, the introduction of La 3+ and Ce 3+ reduces the reaction kinetics of OER, increases the electrochemical surface area of LDH, increases the activity of OER. • Preparation of La/Ce-CoFe LDH by co-precipitation method and simple hydrothermal method. • La/Ce-CoFe LDH shows show excellent OER performance. • The overpotential of 25%La-CoFe LDH is 317 mV with 125 mV/dec Tafel slop at a current density of 10 mA/cm 2 . • The Cdl of 25%La-CoFe LDH (2.46mF/cm 2 ) is nearly 4 timers higher than that of CoFe LDH (0.49mF/cm 2 ).