Study Of Non-noble Metal Catalysts For Hydrogen Production And Oxygen Reduction

Hydrogen fuel cell technology is a high-tech with great economic and strategic significance in the 21st century.However,the sluggish cathodal kinetics of oxygen reduction reaction(ORR)in hydrogen fuel cells requires the use of a large amount of expensive and scarce precious metal platinum(Pt)as the catalyst,which restricts its large-scale commercial application.As for the upstream industry of hydrogen fuel cells,the technology of hydrogen production by electrolysis of water is considered as the most environmental and competitive approaches for high-purity hydrogen preparation.However,the high cost issue cannot be ignored either.Both the hydrogen evolution reaction(HER)and the oxygen evolution reaction(OER)require high cost precious metals as catalysts.Therefore,the development of non-Pt catalysts with low cost,high efficiency and long stability for high-purity hydrogen production and fuel cell-related reactions is the key to breaking the bottleneck of fuel cell technology development.Thus,this paper designed and developed a series of highly efficient and stable non-precious metal catalytic materials based on the premise of low cost and simple preparation process.(1)In the traditional hydrogen production technology by electrolysis,the sluggish OER thermodynamics and kinetics at anode always lead to a large overpotential and demand high energy consumption for water splitting.Moreover,the utilization value of anode product oxygen is low and there is no need to collect it.Replacing the bootless and sluggish oxygen evolution reaction with the oxidation of some more readily oxidized chemical products is a feasible strategy for energy-saving H₂ generation.However,its broad application is inhibited by the costly raw materials,noble-metal catalysts and the toxic effect of organic molecules on catalysts.Herein,we report a novel anti-poisoning MOx/MP(M=Ni,Fe and Mo)bifunctional catalyst that can combine the energy-saving H₂ production with sewage disposal simultaneously by directly electrolyzing the wastewater containing organic molecules.The MOx/MP catalyst expresses a commendable electrocatalytic activity for hydrogen evolution reaction and electrooxidation decomposition of small organic molecules(EDM),as well as a remarkable anti-toxicity for organic molecules and a long-term durability.As compared with traditional water electrolysis,the organic electrolytic system exhibits an excellent cell efficient with a cell voltage reducing of 120 m V and can dramatically allow electrical energy savings up to 8%at 10 m A cm^-2.In addition,this strategy can simultaneously integrate hydrogen generation and the oxidative decomposition of organic matter in industrial wastewater.It is foreseeable that this strategy has strong practicability and development prospects for future industrial renewable clean energy production and wastewater purification technologies.(2)Transition metal and heteroatom co-doped carbon nanomaterials(TM-H-C)has excellent oxygen reduction activity and low production cost,and is considered to be the most promising non-precious metal catalyst to replace the precious metal platinum-based catalyst.However,in the traditional open system,the preparation of TM-H-C by high-temperature pyrolysis easily leads to the loss of precursors,low specific surface area of the catalyst,leading to the reducing and coating of the active sites.Aiming at addressing these shortcomings,a semi-restricted one-step method was used to prepare a N–P–Fe-tridoped non-precious metal catalyst P-Fe NC/CNT.The prepared P-Fe NC/CNT catalyst has a densely packed porous carbon nanotube structure,which greatly increases the specific surface area of the catalyst and at the same time provides a fast channel for electron conduction and supplies high-efficiency mass transport channels for ORR-involved species(e.g.,H⁺,O₂ and H₂O)shuttling back and forth within the P-Fe NC/CNT catalyst.Electrochemical tests show that the P-Fe NC/CNT catalyst displays better ORR activity and electrochemical stability than commercial Pt/C catalysts.Significantly,when applied to a primary Zn–O₂ battery,our catalyst comprehensively outperforms the commercial Pt/C catalyst.In addition,this semi-restricted one-step preparation method for heteroatom-doped porous carbon nanotube catalyst is simple and low cost,which provide a convenient and practical approach for preparation other heteroatom-doped carbon nanotube catalysts.(3)TM-H-C have been mainly accessed by heat-treating heteroatoms,transition metal and carbon precursors with the aid of pore forming template at a relatively high carbonization temperature.However,achieving the atomic-level control of the contents and distributions of doped heteroatoms and metal ions in TM-H-C remains a challenge using conventional synthesis techniques.Moreover,these template-assisted methods always require additional complicated processes to synthesis and remove templates(such as silica,polystyrene spheres or metal oxide),during which,some toxicity reagents may be introduced thus poison the catalysts.Therefore,developing simple processing method to fabricate efficient carbon-based catalysts with favorable doping condition and 3D porous structure is of great significance and highly desired for ORR catalysis.Herein,we report a phytic acid-assisted self-templating strategy to fabricate N–P–Fe-tridoped carbon with a hierarchical porosity.The resultant unique structures and well-designed heteroatoms-doping condition impart final catalysts with enhanced mass transfer ability and abundant available active sites,ensuring high performance in catalyzing ORR.Impressively,the half wave potential of the optimal catalyst is 0.926 V(vs.RHE),which is 40 m V higher than the state-of-art platinum-based catalyst and better than most reported ORR catalysts.