Kawase Yudai, Higashi Tomohiro, Katayama Masao, Domen Kazunari, Takanabe Kazuhiro
Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
Environmental Science Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
ACS Appl Mater Interfaces. 2021 Apr 14;13(14):16317-16325. doi: 10.1021/acsami.1c00826. Epub 2021 Apr 2.
A transparent TaN photoanode is a promising candidate for the front-side photoelectrode in a photoelectrochemical (PEC) cell with tandem configuration (tandem cell), which can potentially provide high solar-to-hydrogen (STH) energy conversion efficiency. This study focuses in particular on the semiconductor properties and interfacial design of transparent TaN photoanodes fabricated on insulating quartz substrates (TaN/SiO), typically the geometric area of 1 × 1 cm in contact with indium on its edge. This material utilizes the self-conductivity of TaN to make the PEC system operational, and the electrode would strongly reflect the intrinsic nature of TaN without a back contact that is commonly introduced. First, PEC measurements using acetonitrile (ACN)/HO mixed solution were made to elucidate the intrinsic photoresponse in the presence of tris(2,2'-bipyridine)ruthenium(II) bis(hexafluorophosphate) (Ru(bpy)(PF)) without water contact which avoids a multielectron-transfer oxygen evolution reaction (OER) and photoinduced self-oxidation. The potential difference between the onset potential of Ru PEC oxidation by TaN/SiO and the redox potential of Ru in the nonaqueous environment was about 0.7 V. While a stable photoanodic response was observed for TaN/SiO in the nonaqueous phase, the addition of a small quantity of water into this nonaqueous system led to the immediate deactivation of TaN/SiO photoanode under illumination by self-photooxidation to form TaO at the solid/water interface. In aqueous phase, flatband potentials estimated from Mott-Schottky analysis varied with solution pH (constant potential against reversible hydrogen electrode (RHE)). Photoelectrode modification by a transparent NiFeO layer was attempted. The complete coverage of the TaN surface with transparent NiFeO electrocatalysts, achieved by an optimized spin-coating protocol with controlled Ni-Fe precursors, allowed for the successful protection of TaN and demonstrated an extremely stable photocurrent for hours without any additional protective layers. The stability of the resultant NiFeO/TaN/SiO was limited not by TaN but mainly by a NiFeO electrocatalyst due to Fe dissolution with time.
透明氮化钽光阳极是具有串联结构的光电化学（PEC）电池中正面光电极的一个有前途的候选材料，该串联电池有可能提供高的太阳能到氢能（STH）能量转换效率。本研究特别关注在绝缘石英衬底（TaN/SiO）上制备的透明氮化钽光阳极的半导体特性和界面设计，其典型的几何面积为1×1平方厘米，边缘与铟接触。这种材料利用氮化钽的自导电性使PEC系统运行，并且该电极在没有通常引入的背接触的情况下能强烈反映氮化钽的固有性质。首先，使用乙腈（ACN）/水混合溶液进行PEC测量，以阐明在存在双（六氟磷酸根）三（2,2'-联吡啶）钌（II）（Ru(bpy)₂(PF₆)）且无水接触的情况下的固有光响应，这避免了多电子转移析氧反应（OER）和光致自氧化。TaN/SiO对Ru进行PEC氧化的起始电位与非水环境中Ru的氧化还原电位之间的电位差约为0.7 V。虽然在非水相中观察到TaN/SiO有稳定的光阳极响应，但向该非水体系中加入少量水会导致TaN/SiO光阳极在光照下通过自光氧化在固/水界面立即失活，形成Ta₂O₅。在水相中，通过莫特 - 肖特基分析估计的平带电位随溶液pH值（相对于可逆氢电极（RHE）的恒定电位）而变化。尝试用透明的NiFe₂O₄层对光电极进行改性。通过使用可控的Ni - Fe前驱体的优化旋涂方案，用透明的NiFe₂O₄电催化剂完全覆盖TaN表面，成功地保护了TaN，并在没有任何额外保护层且数小时内表现出极其稳定的光电流。所得的NiFe₂O₄/TaN/SiO的稳定性不是由TaN限制，而是主要由NiFe₂O₄电催化剂限制，这是由于Fe随时间溶解所致。
