Leiden Institute of Chemistry, Leiden University, PO box 9502, 2300 RA Leiden, The Netherlands.
Phys Chem Chem Phys. 2013 Mar 7;15(9):3196-202. doi: 10.1039/c2cp44620k. Epub 2013 Jan 24.
The current imbalance in the biogeochemical cycle of nitrogen is as serious as that of carbon. One way to mitigate this problem is through the electrochemical reduction of nitrates under mild conditions, which is an appealing though not fully understood process. Therefore, deeper insight into the electrocatalytic reaction mechanism is needed to optimize this process. Here we thoroughly analyse the adsorption energy of nitrate with DFT calculations on various surface facets of pure Au, Ag, and their near-surface and surface alloys, as the adsorption and subsequent reduction of nitrate are thought to be rate limiting in the electrocatalytic reaction. The observed systematic trends allow prediction of the surface with highest electrocatalytic activity for the reduction of nitrate. This prediction was verified experimentally by depositing sub-monolayer amounts of Ag on polycrystalline Au electrodes. We observe a well-defined volcano curve which correlates the amount of Ag deposited on the surface with the current density at a fixed potential, with the peak activity around 2/3 ML Ag surface coverage. The electrocatalytic activity and stability of the bimetallic Ag-Au systems, found through the interplay of theoretical modelling and empirical observations, serve as a clear example for the rational design of novel catalytic materials and confirm the key role that the adsorption of nitrate plays in the overall nitrate reduction rate.
当前氮的生物地球化学循环失衡的严重程度与碳一样严重。缓解这一问题的一种方法是在温和条件下通过电化学还原硝酸盐，这是一种有吸引力但尚未完全理解的过程。因此，需要更深入地了解电催化反应机制，以优化该过程。在这里，我们通过对纯金、银及其近表面和表面合金的各种表面晶面进行密度泛函理论（DFT）计算，彻底分析了硝酸盐的吸附能，因为硝酸盐的吸附和随后的还原被认为是电催化反应中的限速步骤。观察到的系统趋势允许预测对硝酸盐还原具有最高电催化活性的表面。通过在多晶金电极上沉积亚单层量的 Ag 来实验验证了这一预测。我们观察到一个明确的火山曲线，该曲线将表面上沉积的 Ag 量与固定电位下的电流密度相关联，在约 2/3 ML Ag 表面覆盖率处达到峰值活性。通过理论建模和经验观察的相互作用发现的双金属 Ag-Au 体系的电催化活性和稳定性清楚地说明了新型催化材料的合理设计，并且证实了硝酸盐的吸附在整体硝酸盐还原速率中起着关键作用。
