Surface Chemical Properties of Mo2C, W2C, Mo2N and W2N Probed with CO, CO2and O2 Adsorption: A DFT Analysis

作为具有吸引力的电极材料，过渡金属碳化物与氮化物被应用在许多电化学储能及能量转换领域. 本工作中，通过密度泛函理论计算，以及一氧化碳 （CO）, 二氧化碳（CO2）和 氧气（O2）分子的吸附来表征钼和钨的碳化物及氮化物，如碳化钼（Mo2C）、碳化钨（W2C）、氮化钼（Mo2N）和氮化钨（Mo2C）的表面化学性质. 这些探针分子可为研究钼和钨的碳化物及氮化物表面在酸性/碱性的氧化还原性质提供衡量方法. 计算结果表明，CO2分子的吸附发生在路易斯碱位，其碱性降低顺序为α-W2C(001) > α-W2N(001) > β-Mo2C(001) > γ-Mo2N(100). 此外，CO和O2分子吸附可用于评估上述碳化物及氮化物的还原能力，其还原性减小顺序为β-W2C(100) > α-Mo2C(100) > α-W2N(001) > α-W2C(001) > β-Mo2C(001) > γ-Mo2N(100). 由于还原本性，使得上述这些碳化物和氮化物成为在各种催化反应中有可能取代贵金属的良好候选材料.Transition metal carbides and nitrides are attractive materials for electrodes in many electrochemical energy storage and conversion applications. In the present study, we use density functional theory slab calculations to characterize the surface chemical properties of molybdenum (Mo) and tungsten (W) carbides and nitrides, namely, Mo2C, W2C, Mo2N and W2N with the adsorption of CO, CO2 and O2. These probing molecules provide measures of in both acidity/basicity and redox property of for the surfaces of these carbides and nitrides. Our results show that Lewis basic sites were responsible for CO2 adsorption and the basicity follows followed an order of α-W2C(001) > α-W2N(001) > β-Mo2C(001) > γ-Mo2N(100). Both CO and O2 adsorption provide measures of in the reducing ability of these carbides and nitrides. The results showed a reducing ability in the order of β-W2C(100) > α-Mo2C(100) > α-W2N(001) > α-W2C(001) > β-Mo2C(001) > γ-Mo2N(100). The reducing nature of these carbides and nitrides make them good candidates to substitute noble metals in various catalytic reactions.We acknowledge the support of NSF-CBET program (Award no. CBET-1438440).We acknowledge the support of NSF-CBET program (Award no. CBET-1438440).作者联系地址：美国南伊利诺伊大学化学与生物化学系, 卡本代尔, 伊利诺伊 62901Author's Address: Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL 62901, US