Fabrication Of TiB₂-Based Room-Temperature Ferromagnetic Catalysts And Their Magnetoelectric Coupling Catalytic Hydrogen Production Performance

Energy is the material support for human survival,but the overuse of fossil fuels has made the problem of energy shortage increasingly serious.As one of the most promising green and sustainable energy carriers,hydrogen is considered as an ideal candidate to meet the growing demand for clean and efficient energy supply.An excellent catalytic hydrogen production system not only requires high catalytic performance and low cost,but also requires good selectivity for dehydrogenation reactions.Among them,electrochemical hydrocracking for hydrogen production is considered as one of the most convenient and economical methods to solve the energy crisis and meet the demand for clean and green energy development in the future.However,the slow oxygen evolution reaction（OER）kinetics and the high cost of hydrogen evolution reaction（HER）are issues that largely limit their industrial application.Secondly,formic acid（HCOOH,FA）has received increasing attention in the field of hydrogen production due to its high H₂ energy density（4.4 wt%）,room temperature stability and wide range of sources.However,the development of a low-cost,recyclable and efficient catalyst material for green hydrogen production from HCOOH at room temperature has always been a challenge.In response to the above issues,two aspects of the study are carried out in this thesis.Firstly,we have successfully developed a room-temperature intrinsic ferromagnetic TiB₂,adopting a new approach of magnetoelectric coupling with controllable electrochemical performance.By utilizing its two major endogenic properties of electron charge and spin,we have achieved an improvement in the bifunctional catalytic performance of OER and HER.Secondly,strong metal-support interaction（SMSI）is a key strategy to improve the adsorption performance and electronic states on the surface of metal-loaded catalysts,thereby affecting their catalytic activity and stability.In order to solve the problems of high cost,difficult recovery and poor stable recyclability of powder catalysts in HCOOH dehydrogenation,this paper uses ferromagnetic TiB₂ as a carrier and Pt Ni alloy loaded with synergistic effect based on SMSI effect loads Pt Ni alloy with synergistic effect to construct SMSI effec to achieve efficient and stable catalysis of HCOOH at room temperature and substantially improve its recoverability.The main research contents are as follows:（1）A room-temperature intrinsic ferromagnetic TiB₂ material without doping is discovered using a high-temperature molten salt method with fixed mass ratio of TiO₂,B powder,Na Cl and KCl.By utilizing its excellent properties such as high Curie temperature and tunable magnetic moment,a low-cost OER/HER bifunctional electrocatalytic performance enhancement has been achieved in alkaline solutions.It has been shown that TiB₂ with two-dimensional layered crystal structure and topological semi-metallic properties can undergo spin polarization due to the surface Tisuspension bond under the action of magnetic field.Combined with the Vibrating Sample Magnetometer（VSM）test that the saturation magnetization intensity of TiB₂after calcination is as high as 0.74 emu g^-1,which is 2 orders of magnitude higher than that of the same period last year;Both Zero Field Cooling-Field Cooling（ZFC-FC）experiment and Magnetization-Temperature（M-T）curve confirm that TiB₂ is an intrinsic ferromagnetic material with a Curie temperature of up to 350 K.To further improve the magnetization strength of TiB₂,palladium nanorods（Pd NR）with one-dimensional properties and tip effect are loaded on the carrier.TiB₂ and Pd NR/TiB₂ exhibit different degrees of OER/HER performance enhancement after magnetization.Moreover,thanks to the ferromagnetism and adsorption properties of the catalyst,the cathode current density of Pd NR/TiB₂ directly increase from the initial 2 mA cm^-2 to 74.5 mA cm^-2 after magnetization and have a maximum C_dl of 0.025μF cm^-2(higher than the unmagnetized Pd NR/TiB₂:0.006μF cm^-2).This work finds a room-temperature ferromagnetic material that does not require defect modulation and magnetic doping,accelerating the development of electrocatalytic applications promote by magnetic fields and the reversible enhancement of OER/HER bifunctional electrocatalysis under alkaline conditions.（2）A series of PtNi alloys with molar ratios are prepared by a simple hydrothermal method,and the alloy nanoparticles are anchored on TiB₂ carriers with room-temperature ferromagnetism and large active specific surface area by initial impregnation method and calcination treatment.Among them,the Pt₃Ni₈/TiB₂ material calcine at 600℃ for 3 h catalyze 10.0 M aqueous formic acid solution at room temperature with a turnover frequency（TOF）value up to 175 h^-1,which is much higher than that of the monometallic loaded catalysts and is 124%to 187.8%of the performance of Pt-based catalysts containing additives under year-on-year conditions.It is shown that thanks to the synergistic effect of the alloy,which results in a shortened bond length,Ni can transfer more electrons to Pt.In addition,the temperature-induced TiB₂ under the action of SMSI wraps the alloy well,avoiding CO poisoning,and the TiB₂ overlay becomes the active site.The adsorption nature and electronic state of the catalyst surface are also modified,and then the Pt₃Ni₈/TiB₂ catalyst with high catalytic activity,stability and selectivity is obtained.Moreover,the ferromagnetic catalyst is more easily absorbed by external magnets and can still approach the initial catalytic activity after five cycles of testing.Its excellent recyclability and stability are attributed to the addition of non-noble metal Ni elements,and the presence of magnetic interactions in Pt₃Ni₈ alloy further improves the magnetization strength of TiB₂(0.76emu g^-1).Therefore,designing experiments to load the alloy onto a ferromagnetic effective carrier with high specific surface area can not only achieve efficient and stable catalysis,improve its recycling rate,but also reduce the amount of noble metals and reduce the cost of catalysts.