Li Xingguo group of Peking University has made new progress in the research of rare earth metal alloys and Their Hydrides

Metal hydrogen storage materials represented by rare earth, magnesium and other metals are relatively traditional research fields, and there are relatively few academic breakthroughs in recent years Recently, Li Xingguo research group of Peking University found that metal hydrogen storage materials have unique applications in some important and interesting electrochemical systems, which gives this traditional material system new opportunities 1 Enhanced energy efficiency of direct borohydride fuel cell (DBFC) is a kind of important high energy density liquid fuel cell Its anode reaction is the oxidation of BH 4 -, in which the escape of hydrogen is the largest side reaction, resulting in a huge loss of energy efficiency The researchers made y-pd film as hydrogen storage / catalytic dual function electrode, which effectively inhibited hydrogen production by using the reversible hydrogen storage performance of Y hydride, and improved the energy efficiency of DBFC by 40% (Figure 1) Fig 1 Inhibition of hydrogen storage / catalytic bifunctional electrode of y-pd on H 2 production in BH 4-oxidation process and its mechanism (source: J mater Chem A, 2017, 5, 14310-14318.) 2 Metal hydrolysis battery: hydrogen production by aluminum hydrolysis is an important way of hydrogen production in the hydrogen absorption process of power generation, but the heat generated by aluminum hydrolysis even exceeds the chemical energy contained in the generated hydrogen, up to 55% of the chemical energy is directly dissipated by heat The researchers use the y-pd film electrode and Al sheet to form a battery, which can convert the hydrolyzed heat energy into electric energy, and the utilization rate of hydrolyzed heat energy reaches 8% - 15% In this process, the y-film synchronously absorbs hydrogen, realizing synchronous power generation and hydrogen absorption for the first time (Figure 2) Figure 2 Working principle of aluminum hydrolysis battery, synchronous change process of transmittance and potential of y-pd film electrode (angel W chem Int ed, Doi: 10.1002/anie.201711666) in the above two parts of work, the hydrogen storage material plays the role of "hydrogen buffer pool", so it is required that the hydrogen storage material has excellent hydrogen absorption and desorption reversibility and kinetics, but the requirement for hydrogen storage capacity is not high The classic rare earth hydrogen storage alloy is perfect for the above application In this paper, the mechanism of hydrogen absorption and desorption of rare earth hydrogen storage materials in NiMH batteries was studied in situ by optical method, based on the characteristic of hydrogen induced phototransformation (i.e hydrogen induced metal semiconductor phase transition) of thin film electrodes 3 In the process of lithium storage, h and Li + can only form LiH in the proportion of 1:1 However, in the composite system of Rare Earth Hydride reh3 (re = y, La, GD) - graphite, the ratio of H / Li + can reach 1:5 through the synergistic effect with graphite The experiment shows that the addition of reh3 can make the specific capacity of the composite system reach 800 MAH / g, and has very good cycle performance As shown in Figure 3, active hydrogen acts as a negative center in the lithium insertion process, reducing the energy of the system after lithium insertion The Li embedded structure of the negative electrode is no longer the lic6 of graphite, but the formation of li5c16h, so hydride modification can greatly improve the lithium storage capacity of graphite Figure 3 Schematic diagram of lithium storage mechanism of reh3 / C system (source: adv mater., 2018, 30, 1704353) 4 Low cost preparation of light metals such as Mg and Na by reactive ball milling to achieve high quality nano silicon is also a common hydrogen storage metal, and also a strong reductant Using its strong reducibility, researchers can reduce cheap silicon materials such as SiO2 and SiCl4 to obtain high-quality nano silicon powder through room temperature ball grinding reaction Its particle size is only 25-50 nm and its distribution is uniform As a negative electrode of lithium-ion battery, it shows high capacity and cycle stability (Figure 4) Nano silicon is the most attractive anode of next generation high capacity lithium battery, but the material cost is still very high This achievement can greatly reduce the cost of nano silicon, and it is easy to enlarge At present, we are actively carrying out amplification experiments Figure 4 Efficient preparation of nano silicon powder by reactive ball milling with Mg and SiO2 as raw materials (source: ACS Nano, 2017, 11, 6065 − 6073) Chen Jun, Xiao Rui, Zheng Xinyao and Liu Zhiliang, Ph.D students of Peking University, are the first authors of the above-mentioned papers respectively The series of research is in the charge of Professor Li Xingguo and Associate Professor Zheng Jie, and has been completed in cooperation with Professor Zhou Henghui of Peking University, with the support of NSFC and Ministry of science and technology Paper link: http://onlinelibrary.wiley.com/doi/10.1002/anie.201711666/abstract profile of Professor Li Xingguo: http://old.chem.pku.cn/page/lixg/professional.html profile of Associate Professor Zheng Jie: http://old.chem.pku.edu.cn/page/lixg/personal/zhengjie/zhengjie.cn.htm Associate Professor Zheng Jie