Ge Yulu, Lyu Zhenhua, Marcos-Hernández Mariana, Villagrán Dino
Department of Chemistry and Biochemistry, The University of Texas at El Paso El Paso TX 79968 USA
Chem Sci. 2022 Jul 4;13(29):8597-8604. doi: 10.1039/d2sc01250b. eCollection 2022 Jul 29.
Water splitting is considered a promising approach for renewable and sustainable energy conversion. The development of water splitting electrocatalysts that have low-cost, long-lifetime, and high-performance is an important area of research for the sustainable generation of hydrogen and oxygen gas. Here, we report a metal-free porphyrin-based two-dimensional crystalline covalent organic polymer obtained from the condensation of terephthaloyl chloride and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin which is stabilized by an extensive hydrogen bonding network. This material exhibits bifunctional electrocatalytic performance towards water splitting with onset overpotentials, , of 36 mV and 110 mV for HER (in 0.5 M HSO) and OER (in 1.0 M KOH), respectively. The as-synthesized material is also able to perform water splitting in neutral phosphate buffer saline solution, with 294 mV for HER and 520 mV for OER, respectively. Characterized by electrochemical impedance spectroscopy (EIS) and chronoamperometry, the as-synthesized material also shows enhanced conductivity and stability compared to its molecular counterpart. Inserting a non-redox active zinc metal center in the porphyrin unit leads to a decrease in electrochemical activity towards both HER and OER, suggesting the four-nitrogen porphyrin core is the active site. The high performance of this metal-free material towards water splitting provides a sustainable alternative to the use of scarce and expensive metal electrocatalysts in energy conversion for industrial applications.
水分解被认为是一种用于可再生和可持续能源转换的有前景的方法。开发具有低成本、长寿命和高性能的水分解电催化剂是可持续生产氢气和氧气的一个重要研究领域。在此，我们报道了一种无金属的基于卟啉的二维结晶共价有机聚合物，它由对苯二甲酰氯和5,10,15,20-四(4-氨基苯基)卟啉缩合而成，并通过广泛的氢键网络得以稳定。这种材料对水分解表现出双功能电催化性能，对于析氢反应（在0.5 M H₂SO₄中）和析氧反应（在1.0 M KOH中），起始过电位分别为36 mV和110 mV。合成的材料在中性磷酸盐缓冲盐溶液中也能够进行水分解，析氢反应和析氧反应的过电位分别为294 mV和520 mV。通过电化学阻抗谱（EIS）和计时电流法表征，合成的材料与其分子对应物相比还表现出增强的导电性和稳定性。在卟啉单元中插入一个非氧化还原活性的锌金属中心会导致对析氢反应和析氧反应的电化学活性降低，这表明四氮卟啉核心是活性位点。这种无金属材料在水分解方面的高性能为工业应用的能量转换中使用稀缺且昂贵的金属电催化剂提供了一种可持续的替代方案。
