Research On The Properties And Catalytic Mechanism Of Molybdenum Sufide/Carbon And Sulfur/Carbon Composite Electrodes

Both of the molybdenum sulfide and sulfur(S) are earth-abundant and low-cost materials. It is of great significance to reasearch on their applications in renewable energy field, because theory calculation indicates the molybdenum sulfide might replace Pt catalyst for hydrogen evolution reaction with the highest potential, and nanostructured Mo S2 anode and S cathode exhibit 1000 m Ah/g higher real capacity. The molybdenum sulfide deposited on different carbon substrates and Sulfur/ carbon nanofiber(S/CNF) were prepared by chemical vapor deposition(CVD) method. The laws of electrochemical performances, which could be affected by the morphologies, ingredients and structures, were studied and explored. Furthermore, the electrochemical mechanism and stress crrosion mechanism of molybdenum sulfide HER catalysts were investigated.For the hydrogen evolution reaction(HER), we elucidate the dominant factors essentially related with the catalytic activity and regularity of the molybdenum sulfide catalysts by the comparing and analyzing the HER performances of molybdenum sulfide catalysts, which were fabricated from 200 ℃ to 850 ℃ on different carbon sunstrates, such as glassy carbon(GC)、Mo S2/GC、Graphite、graphene nano-platelet(GNP/GC). The composition and crystallinity play key roles in the catalytic performance of molybdenum sulfide for HER. Amorphous Mo S3 has much better activity than high crystallinity Mo S2, but micro-crystallinel Mo S2+x showed better stability than amorphous Mo S3. We abserved a reactivation process for the amorphous Mo S3, it is critical for the improvement of catalytic performance to know the real ingredients and true active cites. By systematically analyzing the catalytic performance of molybdenum sulfide with different composite, crystallinity, surface properties, we demonstrate the physical feature— the actual surface area(capacitance) increase derived from corrosion play the key roles for the activation, but the components transformantion does not matter much. After understanding the connection of HER durability and surface mechanical properties of the catalysts in between, the stress corrosion mechanism of Mo S3 film was investigated. We found out a effective strategy to achieve high catalytic performance and good stability by employing GNP as supports to create an excellent electrocatalysts with low-electrical-loss contact, minimal mass transport limitation, and maximal active sites. The overpotential only-0.165 V vs RHE(reversible hydrogen electrode) was required to produce 10 m A/cm2, merely decreases by 1 m V after 10,000 potential cycles. The high stability of the Mo Sx electrocatalyst offers an excellent approach to improve the reliability and durability of HER catalysts.As for the study of electrodes for batteries, a carbon nanotube-Mo S2(Mo S2/CNF) composite anode and a S/CNF composite cathode were prepared successfully by CVD. The 2H crystal Mo S2 showed a leaf-like and network structure grown on the CNT, which exhibited 1220 m Ah/g for the first cycles as anode material for lithium ion battery, 1231 m Ah/g after 68 th cycles and 99% coulombic efficiency; The as-designed and developed S/CNF cathode had a unique self-inhibiting, gradient sulfur structure, exhibited high sulfur loading(2.6 mg cm-2) and high sulfur content(65%) with a stable capacity of > 700 m Ah g-1, which will be a robust, novel and highly applicable electrode materials for Li-S battery.