Dues Christof, Schmidt Wolf Gero, Sanna Simone
Institut für Theoretische Physik and Center for Materials Research (LaMa), Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 16, 35392 Gießen, Germany.
Department Physik, Universität Paderborn, Warburger Str. 100, 33098 Paderborn, Germany.
ACS Omega. 2019 Feb 21;4(2):3850-3859. doi: 10.1021/acsomega.8b03271. eCollection 2019 Feb 28.
Water splitting is a highly promising, environmentally friendly approach for hydrogen production. It is often discussed in the context of carbon dioxide free combustion and storage of electrical energy after conversion to chemical energy. Since the oxidation and reduction reactions are related to significant overpotentials, the search for suitable catalysts is of particular importance. Ferroelectric materials, for example, lithium niobate, attracted considerable interest in this respect. Indeed, the presence of surfaces with different polarizations and chemistries leads to spatial separation of reduction and oxidation reactions, which are expected to be boosted by the electrons and holes available at the positive and negative surfaces, respectively. Employing the density functional theory and a simplified thermodynamic approach, we estimate the overpotentials related to the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on both polar LiNbO (0001) surfaces. Our calculations performed for ideal surfaces in vacuum predict the lowest overpotential for the hydrogen evolution reaction (0.4 V) and for the oxygen evolution reaction (1.2 V) at the positive and at the negative surfaces, respectively, which are lower than (or comparable with) commonly employed catalysts. However, calculations performed to model the aqueous solution in which the reactions occur reveal that the presence of water substantially increases the required overpotential for the HER, even inverting the favorable polarization direction for oxidation and reduction reactions. In aqueous solution, we predict an overpotential of 1.2 V for the HER at the negative surface and 1.1 V for the OER at the positive surface.
水分解是一种极具前景的、环境友好的制氢方法。它经常在无二氧化碳燃烧以及将电能转化为化学能后进行存储的背景下被讨论。由于氧化和还原反应与显著的过电位相关，寻找合适的催化剂尤为重要。铁电材料，例如铌酸锂，在这方面引起了相当大的关注。事实上，具有不同极化和化学性质的表面的存在导致还原和氧化反应的空间分离，预计分别由正表面和负表面处可用的电子和空穴来促进这些反应。利用密度泛函理论和一种简化的热力学方法，我们估计了在两个极性LiNbO(0001)表面上与析氧反应（OER）和析氢反应（HER）相关的过电位。我们对真空中的理想表面进行的计算预测，在正表面和负表面上析氢反应的最低过电位分别为0.4 V和析氧反应的最低过电位为1.2 V，这低于（或与）常用催化剂相当。然而，为模拟反应发生的水溶液而进行的计算表明，即使水的存在会使氧化和还原反应的有利极化方向反转，水的存在也会显著增加HER所需的过电位。在水溶液中，我们预测负表面上HER的过电位为1.2 V，正表面上OER的过电位为1.1 V。
