Design, Synthesis And Performances Of Several Base Metal Hybrid Electrocatalysts

Over-dependence on the fossil fuel brings not only ecological problem but also negative infulences on the global economy and society. It is eager to develop renewable energy source forward for mankind’s development. Fuel cell, as an electrochemical device for direct conversion the chemical energy into electricity, due to the high energy conversion efficiency, zero emission, alternative fules and wide-range use, it is expected as the most promising sustainable energy device. However, the most important issue of commercialization of fuel cells is the high cost catalysts and insufficient noble metal reserves. Therefore, developing new low cost, high activity, robust stability alternative few-/non-noble metal composite catalysts is highly needed. In this dissertation, we will focus our research interest on this topic. We firstly introduced several vital electrochemical reaction processes related to energy conversion, and summarized the research progress on the development of the few-/non-noble metal hybrid composite catalysts for the electrochemical reactions, particularly highlighted the progress on designing and synthesis new low-cost carbon-based or transition metal chalcogenides hybrid composite electrocatalysts. Of note, for large-scale applications in energy conversion the developed electrocatalysts fall short in one or more of the requirements for the important electrochemical reactions. Based on this, we rationally select low-cost, high yield, catalytic prospect transition metal chalcogenides as the major object. Through "chemical hybrid" route, combine them with other suitable functional nanomaterials to obtain a series hybrid composite, dut to the stronge chemical coupling effect and the modified electronic structure, we can improve the hybrid catalytic performance to meet the practical application. The main achievements can be summarized as follows:1. We hybrided CoSe2/DETA (DETA= diethylenetriamine) nanobelts with CeO2 nanocrystal obtained CoSe2/CeO2 hybrid nanobelts. We found that the new hybrid composite still kept the original ultrthine, lamellar and belt-like structure, which could obviously enhanced the catalytic performance of the CoSe2/CeO2 hybrid catalytst. Discussed the modification of the CoSe2/DETA electronic structure after decorating CeO2, and found that the CoSe2/CeO2 perpormed excellent electrocatalytic OER performance compare with original CoSe2/DETA nanobelt. We attributed the improved catalytic performance to the chemical synergistic effect and the unique surface structure of CeO2 with high mobility of oxygen vacancies.2. Developed a CoSe2/carbon quantum dots hybrid nanocomposite. We selected the lamellar mesostructured CoSe2/DETA nanobelts as the major material, introduced the CDs during the nuclear and growth of the CoSe2/DETA nanobelts, and synthesized a new CoSe2/CDs hybrid nanocomposite. The semi-crystalline CDs embedded in CoSe2/DETA nanobelts could change the original phase, and formed a polymorphic phase structure combined the cubic with orthorhombic phase. We found that the new orthorhombic structure would change the coordination number of Co and modified the electronic structure. After hybrid with CDs, the composite structure disorder increased and reduced the surface energy. The CoSe2/CDs hybrid nanocomposite perfomed excellent HER and OER catalytic performance, which could be a promising electrocatalyst for the practical water splitting technology.3. We selected the large-scale porous commercial 3D carbon fiber felt (CFF) as the substrate, in-suit decorated CoSe2/DETA nanobelts on the carbon fiber surface, and prepared a 3D CoSe2/CFF hierarchical electrode as the cathode for hydrogen production. We found that the 3D CoSe2/CFF perfomed exceptionally high catalytic activity (141 mV overpotential to afford current density of 10 mA cm-2, a high exchange current density of 5.9×10-2 mA cm-2). It also exhibits excellent catalytic stability, which could be performed more than 30,000 potential cycles with no decrease of the current density.4. We developed a one-step route for directly prepare carbon-supported PtCoNi ternary alloy nanoparticles. We found that at higher annealed temperature, Pt and Ni atoms in PtCoNi ternary alloy nanoparticles would migrate to the outer surface and formed a PtNi-enriched surface structure, which could increase the noble metal Pt utilization rate. After alloy Pt with Co and Ni, the electronic structure of Pt and downshift of the d-band center position, thus radically improved the ORR catalytic performance. We explored the structure modification of the catalyst during the electrocatalytic process.