Study On Water Oxidation Performance Of Layered Manganese Oxide And Metal Porphyrin Composites

With the development of society and economy,the demand of energy is significant increase.The traditional energy sources are running out,thus the clean,efficient and renewable energy has been attracted extensive attention.In the numerous of hydrogen production technology,water splitting technology using the solar is very outstanding.This process needs to use a great deal of protons and electrons as reducing agents.Water oxidation can provide a large number of protons and electrons for this process.Therefore,water oxidation is the critical step for hydrogen production technology.However,water oxidation is thermodynamically uphill and require high energy input without a catalyst.Therefore,it is necessary to develop an efficient,stable,and inexpensive catalyst for promoting oxygen evolution reactions(OER).Oxygen evolution reaction(OER),part of the water oxidation,is limited by catalysts of Pt,RuO2 and IrO2.The main reason is that those metal oxides are precious and scarce which hinder extensive applications.The chemical properties(e.g.chemical composition,pore structures and crystal structure)of manganese oxides have dramatic effect on their catalytic activities.Many studies promoted OER activity by utilizing the same type or a broad variety of manganese oxygen catalysts.The birnessite belongs to ?-type layered manganese oxygen catalysts.The layered structure is formed by edge-sharing manganese octahedral(MnO6).Due to the presence of both Mn3+ and Mn4+ within the structure,and the overall layered structure is negatively charged.Birnessite is usually filled with Na+ in the interlayer to maintain electrically neutral.The interlayer region of birnessite not only contains alkali metal ions,but also contains water molecules.The electron transfer rate of birnessite in the layer is far above the theoretical result.However,poor performance of birnessite containing Na' on oxygen evolution reaction hindered its research.In order to solve the above problems and improve its OER activity,we have done the following work:1.High-purity birnessites were prepared respectively with complexing agent EDTA at room temperature.The products were then exchanged for H+ in an acidic solution,and synthetic birnessite containing only H+.After that,tetramethylammonium hydroxide was added to exchange tetramethylammonium ions with H+.The resulting interlayer spacing was expanded and then rinsed with deionized water to give a stripped state of birnessite nanoplatelets.The positively charged MnTAPP was synthesized and the two were placed in a beaker and stirred to reconstitute them into a new type of conductive composite material.2.the prepared material was used to oxygen evolution reactions.Inserting a positively charged MnTAPP into the layered layer of MnO2 not only improves the electrical conductivity of birnessite,but also improves its stability.Test results show that the new material exhibits superior OER performance.The potentials follow an ascending order of MnTAPP@bir(V= 1.82)<bimessite at 5mA cm-2 current density,whereas the electrocatalytic activities follow an inverse trend,mainly because MnTAPP@bir had a larger surface area that exposed more active sites on the surface.The stabilities of MnTAPP@bir was tested by chronoamperometry,it exhibit stable performance for 4000 s.3.Manganese sulfate was used as a source of manganese to prepare birnessite which contained different alkali metal ions(Li-Bir Na-Bir and K-Bir)by air oxidation method.The activities of water oxidation were enormous different by changing ion species in the layered structure.Li-Bir exhibits superior activity and stable performance.The surface area of Li-Bir(107.282 cm2 g-1)was much bigger than that of Na-Bir(35.623)and K-Bir(11.900).The results showed that the main factors affected the OER activities were the specific surface areas.