Vanadium-Based Nanostructures as High-Performance Catalysts for Water Electrolysis

钒基纳米结构作为高性能电解水催化剂

杨明阳

11553017

博士

应用物理及材料工程

卢周广

2019-11-20

2019-12-20

澳门大学

澳门

Electrically driven water splitting has been considered as one of the most promising methods to produce hydrogen without carbon emission and other pollution gases. However, searching for high-performance electrocatalysts with low cost for water electrolysis is still a huge challenge. Vanadium element plays an important role to tune catalytic performance of electrocatalysts by modifying the electronic structure and enhancing active sites. In this dissertation, we focused on the study about vanadium- based materials including vanadium self-intercalated C/V1.11S2 nanosheets, Co1–xVx hydroxide nanoneedles, and ternary Co1–xVxP nanoneedle arrays as novel catalysts for electrically driven water splitting. Besides, a mixed vanadate, rGO@Ni3V2O8 nanocomposite, was also investigated as anode materials for Li ion battery. The main findings are summarized as below: Firstly, we prepared vanadium self-intercalated C/V1.11S2 nanosheets via a hydrothermal method in combination with a heat treatment. In the experiment, PVP was added, which acted as surfactant to control the size of vanadium sulfide and carbon source to reduce the vanadium sulfide into vanadium self-intercalated V1.11S2 phase with rich active sites. We found that the as-prepared C/V1.11S2 nanosheets showed an excellent electrocatalytic activity with a low onset potential of 15 mV vs. RHE (reversible hydrogen electrode), small Tafel slope of 51 mV dec–1, and prominently catalytic stability. Furthermore, the first-principle calculations confirmed that V1.11S2 has a much lower Gibbs free energy for hydrogen adsorption (ΔGH) than that of VS2. Secondly, we synthesized Co1–xVx hydroxide nanoneedles on nickel foam (NF@ Co1– xVx HNNs) for OER application by a hydrothermal process. We showed that the incoporation of V could effectively reduce the size of the Co1–xVx (0 < x < 1) hydroxide nanoneedle and simultaneously modulate their electronic properties. As a result, the Co1–xVx hydroxide nanoneedles showed enhanced OER catalytic ability over the Co hydroxide nanoneedle. Particularly, the freestanding NF@Co0.75V0.25-HNNs showed the optimum OER catalytic activity and has a low overpotential (268 mV at 10 mA cm–2), a small Tafel slope (80 mV dec–1) and long-term stability, which are comparable to other Co-based and V-based electrocatalysts for OER reported in literatures. Thirdly, we fabricated a novel type of ternary Co1–xVxP nanoneedle arrays with porous structure on nickel foam, which was evaluated as robust electrocatalysts toward alkaline HER under large current density. Combined with the enhanced intrinsic activity, large active surface area and fast reaction kinetics, our NF@Co1–xVxP catalyst delivered a remarkably catalytic ability with low overpotentials of 46, 115, and 226 mV at current densities of 10, 100, and 400 mA cm−2, respectively, as well a small Tafel slope value of 64 mV dec−1 and superior stability in 1 M KOH. At last, ultrafine Ni3V2O8 nanoparticles were anchored on reduced graphene oxide by a hydrothermal method and calcination process to produce a rGO@Ni3V2O8 nanocomposite. This hierarchical architecture of can effectively facilitate charge transfer, maintain structural integrity and accommodate the volume variation during cycling. As a result, the rGO@Ni3V2O8 composite manifested a very stable and high reversible capacity of 1050 mA h g–1 over 200 cycles at a current density of 500 mA g–1 and 900 mA h g–1 after the subsequent 200 cycles at 1 A g–1. Furthermore, excellent rate capability was achieved. More than 45% of the capacity was retained when the current density was increased from 0.1 to 10 A g–1. In summary, vanadium-based materials, including sulfide (vanadium self-intercalated C/V1.11S2 nanosheets), hydroxide (Co1–xVx hydroxide nanoneedles), and phosphides (ternary Co1–xVxP nanoneedle arrays) were synthesized and evaluated as catalysts in the electrolysis of water. The vanadium self-intercalation or vanadium incorporation strategy could effectively promote the intrinsically catalytic performance via modifying electronic structures and enhance active sites by tuning surface morphologies of the electrocatalysts. Further, the integration of Co1–xVx hydroxide and ternary Co1–xVxP nanoneedle arrays on high conductive nickel foam substrate facilitated fast electron charge transfer between the electrode/electrolyte interface. It is expectable that vanadium-based electrocatalysts may replace the expensive Pt for applications into electrolysis in the future.

英语

联合培养

南方科技大学

Yang MY. Vanadium-Based Nanostructures as High-Performance Catalysts for Water Electrolysis[D]. 澳门. 澳门大学,2019.