Bansal Deepak, Cardenas-Morcoso Drialys, Boscher Nicolas
Materials Research and Technology Department, Luxembourg Institute of Science and Technology 28 Avenue des Hauts-Fourneaux Esch-Sur-Alzette Luxembourg
J Mater Chem A Mater. 2023 Jan 26;11(10):5188-5198. doi: 10.1039/d2ta07748e. eCollection 2023 Mar 7.
Directly fused nickel(ii) porphyrins are successfully investigated as heterogeneous single-site catalysts for the oxygen evolution reaction (OER). Conjugated polymer thin films from Ni(ii) 5,15-(di-4-methoxycarbonylphenyl)porphyrin (pNiDCOOMePP) and Ni(ii) 5,15-diphenylporphyrin (pNiDPP) showed an OER onset overpotential of 270 mV, and current densities of 1.6 mA cm and 1.2 mA cm at 1.6 V RHE, respectively, representing almost a hundred times higher activity than those of monomeric thin films. The fused porphyrin thin films are more kinetically and thermodynamically active than their non-polymerized counterparts mainly due to the formation of conjugated structures enabling a dinuclear radical oxo-coupling (ROC) mechanism at low overpotential. More importantly, we have deciphered the role of the porphyrin substituent in the conformation and performance of porphyrin conjugated polymers as (1) to control the extension of the conjugated system during the oCVD reaction, allowing the retention of the valence band deep enough to provide a high thermodynamic water oxidation potential, (2) to provide a flexible molecular geometry to facilitate O formation from the interaction between the Ni-O sites and to weaken the π-bond of the *Ni-O sites for enhanced radical character, and (3) to optimize the water interaction with the central metal cation of the porphyrin for superior electrocatalytic properties. These findings open the scope for molecular engineering and further integration of directly fused porphyrin-based conjugated polymers as efficient heterogeneous catalysts.
直接稠合的镍（II）卟啉作为析氧反应（OER）的多相单中心催化剂已被成功研究。由镍（II）5,15-（二-4-甲氧基羰基苯基）卟啉（pNiDCOOMePP）和镍（II）5,15-二苯基卟啉（pNiDPP）制成的共轭聚合物薄膜显示出270 mV的OER起始过电位，在1.6 V RHE下的电流密度分别为1.6 mA cm²和1.2 mA cm²，其活性几乎是单体薄膜的一百倍。稠合卟啉薄膜在动力学和热力学上比未聚合的对应物更具活性，这主要是由于共轭结构的形成，使得在低过电位下能够发生双核自由基氧偶联（ROC）机制。更重要的是，我们已经阐明了卟啉取代基在卟啉共轭聚合物的构象和性能中的作用：（1）在化学气相沉积反应过程中控制共轭体系的延伸，使价带保持足够深，以提供高的热力学水氧化电位；（2）提供灵活的分子几何结构，以促进镍-氧位点之间的相互作用形成氧，并削弱*镍-氧位点的π键以增强自由基特性；（3）优化卟啉中心金属阳离子与水的相互作用，以获得优异的电催化性能。这些发现为分子工程以及将直接稠合的卟啉基共轭聚合物进一步整合为高效多相催化剂开辟了道路。
