Preparation And Properties Of Biomass Carbon-Based Composite Electrode

The development and production of renewable clean energy is a major challenge for human beings in the 21st century. Due to efficient, environmentally friendly and other advantages, hydrogen production using electrolysis of water is an important way to solve this problem. However, during the electrolysis of water, the oxygen evolution reaction (OER) has high anode overpotential, which causes energy waste and becomes a bottleneck in the electrolysis of water. The quality of the electrode material can affect the efficiency of water decomposition reaction, and the catalyst of electrode material can affect the over potential. To develop a low overpotential and fast kinetics of the oxygen evolution reaction (OER) catalyst have drawn considerable attention recently. Therefore, the development of a low potential, low cost, high efficiency and environmentally friendly of oxygen evolution catalyst has important practical significance.In this paper, several kinds of transition metals and their hydroxides were supported on the basis of biochar, and their catalytic performance were investigated by electrochemical characterization. This study is mainly including the following aspects:1. Biochar has a wide range of natural resources, low cost and high specific surface area, which has a very wide range of applications. In this chapter, three different kinds of biomass, Indus floc, cotton and hair, were used in preparation of biochar. The obtained biochar were characterized by SEM, XRD and BET. SEM results show that the biochar of the floc has a hollow microtube morphology, cotton is filamentous fiber, and hair is irregular block. BET results show that the biochar of the cotton and floc have a large specific surface area and a relatively concentrated pore size distribution. The specific surface area of cotton and floc were 1345.0 cm2/g and 1050.7 cm2/g, respectively, and the corresponding pore volume was 0.64 cm3/g and 0.49 cm3/g. XRD results show that these three biochar are amorphous carbon. The electrochemical characterization showed that the oxygen evolution characteristics of the prepared biochar were poor due to the chemical inertness of carbon materials, the single pore size distribution and the slow electron transfer efficiency, so it is necessary to modify it.2. Properties of transition metal doped biochar as oxygen evolution material.Transition metals are considered promising, because their theoretically high efficiency,high abundance, low cost and environmentally friendly. However, single metal and its oxides have low specific surface area and low stability. Biochar has relative large specific surface area and chemically inert, which is often used as the base material to load metals. The transition metals Co and Ni mixed with three kinds of biochar were boiled in hot alkali and calcined at high temperature (600 ℃) to synthesize cobalt loaded carbon composite and nickel loaded carbon composite. Then they were characterized by SEM, XRD, BET, and electrochemical method. The XRD results found that the metal ions were reduced into metal in the synthesis process. When the transition metal was incorporated, the pore of the biochar material decreased due to the aggregation of the metal element, the specific surface area of the material was decreased, but the pore distribution became rich, which induced the increase of the electron transfer on biochar surface, and thus greatly increased the OER performance.Co-Floc exhibited the lowest oxygen evolution overpotential (490 mv) in all materials, but after running for 10,000 seconds, the performance was reduced.3. Study of the oxygen evolution performance on the metal hydroxide/bimetallic carbon composite. Ni(OH)2 is one of the research directions of nickel-based oxygen evolution catalysts. Ni(OH)2 has excellent catalytic property, but stability is low.Oxygen evolution catalysts with excellent properties are often combined with other catalysts to improve their performance, which provides an opportunity for the emergence of bimetallic catalysts. In this chapter, Ni(OH)2 was synthesized by using NaOH as precipitant and urea as co-precipitant, and it was found that when the ratio of urea to Ni was 1:1, the effect was the best. The best performance of Ni(OH)2 was combined with biochar, and found that the oxygen evolution potential of the composite material formed by heating was 1.888V. Through the combination of Ni-Co and Fe-Co, loading them on cotton and floc, respectively, and results found that Fe-Co-Cotton has the lowest oxygen evolution potential of 1.793 V.