第一性原理研究O2在TiN4掺杂石墨烯上的氢化

作为一种新型高效质子交换膜燃料电池阴极材料, 金属与N共掺杂的石墨烯因其对氧还原反应具有较高的活性而引起了人们的广泛关注. 采用包含色散力校正的密度泛函理论方法系统地研究了O₂在TiN₄掺杂的Graphene上的吸附, 氢化特性. 结果表明: 1) O₂倾向于以side-on模式吸附在Ti顶位, 形成O-Ti-O三元环结构; 2) O₂在TiN₄-Graphene上更倾向于以分子形式直接氢化, 形式OOH结构, 并进一步解离为O+OH, 反应的限速步为O₂的氢化, 对应的反应势垒为0.52 eV.

First-principles study on the hydrogenation of the O2 on TiN4 embedded graphene

As a kind of clean and high efficient energy conversion devices, the proton exchange membrane fuel cell (PEMFC) is a promising technology for clean and sustainable power generation. Metal-coordinated nitrogen-doped graphene is attractive since its use as a cathode material for the PEMFC. The mechanism of O₂ activation and hydrogenation on TiN₄ embedded graphene has been investigated in terms of the dispersion-corrected density functional theory (DFT-D) method. It is found that: 1) O₂ prefers to stay on top of the Ti atom with the side-on configuration, forming the O-Ti-O three-member ring with an adsorption energy of 4.96 eV. 2) According to the Mulliken atomic charges analysis, the absorbed O₂ molecule are negatively charged by 0.60 e in the side-on configuration. 3) Upon the chemisorption of the O₂ on TiN₄-graphene, there are two possible pathways during the activation of the O₂ molecule: dissociation and hydrogenation. In the dissociation pathway, the adsorbed O₂ molecule is first dissociated into two O atoms, with a fairly big reaction barrier of 0.95 eV and an endothermic reaction energy of 0.20 eV. Subsequently, the two O atoms are hydrogenated into O+OH with a reaction barrier of 0.40 eV and an exothermic reaction energy of 2.46 eV. In the hydrogenation pathway, the reaction barrier of the hydrogenation of the adsorbed O₂ is 0.52 eV. The OOH formed subsequently is dissociated into O+OH with a small reaction barrier of 0.04 eV and an exothermic reaction of 2.14 eV. The hydrogenation pathways of the adsorbed O₂ is more preferable, and the corresponding rate-limiting step of this pathway is the hydrogenation of the O₂ with a reaction barrier of 0.52 eV and an exothermic reaction energy of 0.64 eV.#br#In summary, the preferable path of the hydrogenation reactions of O₂ on TiN₄-Graphene is O_2(ads)+H_(ads) → OOH_(ads)→O+OH_(ads). Current results may be benefitial to the design of new electrocatalyst materials based on graphene.