Ishikawa Atsushi, Murase Fumiya, Tateyama Yoshitaka, Otomo Junichiro
Center for Green Research on Energy and Environmental Materials (GREEN), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
ACS Omega. 2022 Jul 22;7(30):26107-26115. doi: 10.1021/acsomega.2c01222. eCollection 2022 Aug 2.
The catalytic electrochemical synthesis of NH on Ru/BaCeO was investigated using density functional theory. The competition between NH formation and the hydrogen evolution reaction (HER) is a key for a high NH formation rate. Our calculations show that H adsorbs more strongly than N at the Ru particle moiety, while the adsorption of N is stronger than the H adsorption at the Ru/BaCeO perimeter, a model for the triple-phase boundary that is proposed to be an active site by experimental studies. This indicates that, while the HER is more favorable at the Ru particle moiety, it should be suppressed at the Ru/BaCeO perimeter. We also calculated the Gibbs free energy changes along the NH formation and found that the NH formation, the NHNH formation, and the NH formation steps have a relatively large Gibbs energy change. Therefore, these are possible candidates for the potential-determining step. The calculated equilibrium potential ( = -0.70 V, vs RHE) is in reasonable agreement with experiments. We also evaluated the reaction energy (Δ) and the activation barrier ( ) of the NH formation at several sites. Δ and were high at the Ru particle moiety (Δ = 1.18 eV and = 1.38 eV) but became low (Δ = 0.32 eV and = 1.31 eV) at the Ru/BaCeO perimeter. These provide the atomic-scale mechanism how the proton conduction in BaCeO assists the electrochemical NH synthesis.
采用密度泛函理论研究了Ru/BaCeO上NH的催化电化学合成。NH生成与析氢反应（HER）之间的竞争是实现高NH生成速率的关键。我们的计算表明，在Ru颗粒部分，H的吸附比N更强，而在Ru/BaCeO周边，N的吸附比H更强，Ru/BaCeO周边是三相边界的模型，实验研究表明其为活性位点。这表明，虽然HER在Ru颗粒部分更有利，但在Ru/BaCeO周边应受到抑制。我们还计算了NH生成过程中的吉布斯自由能变化，发现NH生成、NHNH生成和NH生成步骤具有相对较大的吉布斯能变化。因此，这些可能是决定电位步骤的候选者。计算得到的平衡电位（=-0.70 V，相对于可逆氢电极）与实验结果合理吻合。我们还评估了几个位点上NH生成的反应能（Δ）和活化能垒（）。在Ru颗粒部分，Δ和较高（Δ=1.18 eV，=1.38 eV），但在Ru/BaCeO周边则变低（Δ=0.32 eV，=1.31 eV）。这些结果提供了BaCeO中的质子传导如何辅助电化学NH合成的原子尺度机制。
