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- ItemThiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium(Weinheim : Wiley-VCH, 2021) Borrelli, Mino; Querebillo, Christine Joy; Pastoetter, Dominik L.; Wang, Tao; Milani, Alberto; Casari, Carlo; Khoa Ly, Hoang; He, Fan; Hou, Yang; Neumann, Christof; Turchanin, Andrey; Sun, Hanjun; Weidinger, Inez M.; Feng, XinliangAlthough being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2-b]thiophene) (pDET) to poly(2,6-diethynylbenzo[1,2-b:4,5-b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2-b:2′,3′-d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm−2 and 120 μA cm−2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron-enriched Cβ of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemTowards a methanol economy based on homogeneous catalysis: methanol to H2 and CO2 to methanol(Cambridge : Soc., 2015) Alberico, E.; Nielsen, M.The possibility to implement both the exhaustive dehydrogenation of aqueous methanol to hydrogen and CO2 and the reverse reaction, the hydrogenation of CO2 to methanol and water, may pave the way to a methanol based economy as part of a promising renewable energy system. Recently, homogeneous catalytic systems have been reported which are able to promote either one or the other of the two reactions under mild conditions. Here, we review and discuss these developments.
- ItemYield—not only Lifetime—of the Photoinduced Charge-Separated State in Iridium Complex–Polyoxometalate Dyads Impact Their Hydrogen Evolution Reactivity(Weinheim : Wiley-VCH, 2020) Luo, Yusen; Maloul, Salam; Schönweiz, Stefanie; Wächtler, Maria; Streb, Carsten; Dietzek, BenjaminCovalently linked photosensitizer–polyoxometalate (PS-POM) dyads are promising molecular systems for light-induced energy conversion processes, such as “solar” hydrogen generation. To date, very little is known of their fundamental photophysical properties which affect the catalytic reactivity and stability of the systems. PS-POM dyads often feature short-lived photoinduced charge-separated states, and the lifetimes of these states are considered crucial for the function of PS-POM dyads in molecular photocatalysis. Hence, strategies have been developed to extend the lifetimes of the photoinduced charge-separated states, either by tuning the PS photophysics or by tuning the POM redox properties. Recently, some of us reported PS-POM dyads based on cyclometalated IrIII complexes covalently linked to Anderson-type polyoxometalate. Distinct hydrogen evolution reactivity (HER) of the dyads was observed, which was tuned by varying the central metal ion M of the POMM (M=Mn3+, Co3+, Fe3+). In this manuscript, the photoinduced electron-transfer processes in the three Ir-POMM dyads are investigated to rationalize the underlying reasons for the differences in HER activity observed. We report that upon excitation of the IrIII complex, ultrafast (sub-ps) charge separation occurs, leading to different amounts of the charge-separated states (Ir.+-POMM.−) generated in the different dyads. However, in all dyads studied, the resulting Ir.+-POMM.− species are short-lived (sub-ns) when compared to reference electron acceptors (e.g. porphyrins or fullerenes) reported in the literature. The reductive quenching of Ir.+-POMM.− by a sacrificial donor, triethyl amine (1 m), to generate the intermediate Ir-POMM.− is estimated to be very efficient (70–80 %) for all dyads studied. Based on this analyses, we conclude that the yield instead of the lifetime of the Ir.+-POMM.− charge-separated state determines the catalytic capacity of the dyads investigated. This new feature in the PS-POM photophysics could lead to new design criteria for the development of novel PS-POM dyads. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- Item1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis, Characterization, Photophysical Studies, and Hydrogen Evolution Catalysis(Weinheim : Wiley-VCH, 2020) Costabel, Daniel; Skabeev, Artem; Nabiyan, Afshin; Luo, Yusen; Max, Johannes B.; Rajagopal, Ashwene; Kowalczyk, Daniel; Dietzek, Benjamin; Wächtler, Maria; Görls, Helmar; Ziegenbalg, Dirk; Zagranyarski, Yulian; Streb, Carsten; Schacher, Felix H.; Peneva, KalinaIn this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3S13]2− clusters in aqueous solution for stable visible light driven hydrogen evolution over three days. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemEngineering grain boundaries at the 2D limit for the hydrogen evolution reaction([London] : Nature Publishing Group UK, 2020) He, Yongmin; Tang, Pengyi; Hu, Zhili; He, Qiyuan; Zhu, Chao; Wang, Luqing; Zeng, Qingsheng; Golani, Prafful; Gao, Guanhui; Fu, Wei; Huang, Zhiqi; Gao, Caitian; Xia, Juan; Wang, Xingli; Wang, Xuewen; Zhu, Chao; Ramasse, Quentin M.; Zhang, Ao; An, Boxing; Zhang, Yongzhe; Martí-Sánchez, Sara; Morante, Joan Ramon; Wang, Liang; Tay, Beng Kang; Yakobson, Boris I.; Trampert, Achim; Zhang, Hua; Wu, Minghong; Wang, Qi Jie; Arbiol, Jordi; Liu, ZhengAtom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs.
- ItemPromoting Photocatalytic Hydrogen Evolution Activity of Graphitic Carbon Nitride with Hole-Transfer Agents(Weinheim : Wiley-VCH, 2021) Indra, Arindam; Beltrán-Suito, Rodrigo; Müller, Marco; Sivasankaran, Ramesh P.; Schwarze, Michael; Acharjya, Amitava; Pradhan, Bapi; Hofkens, Johan; Brückner, Angelika; Thomas, Arne; Menezes, Prashanth W.; Driess, MatthiasVisible light-driven photocatalytic reduction of protons to H2 is considered a promising way of solar-to-chemical energy conversion. Effective transfer of the photogenerated electrons and holes to the surface of the photocatalyst by minimizing their recombination is essential for achieving a high photocatalytic activity. In general, a sacrificial electron donor is used as a hole scavenger to remove photogenerated holes from the valence band for the continuation of the photocatalytic hydrogen (H2 ) evolution process. Here, for the first time, the hole-transfer dynamics from Pt-loaded sol-gel-prepared graphitic carbon nitride (Pt-sg-CN) photocatalyst were investigated using different adsorbed hole acceptors along with a sacrificial agent (ascorbic acid). A significant increment (4.84 times) in H2 production was achieved by employing phenothiazine (PTZ) as the hole acceptor with continuous H2 production for 3 days. A detailed charge-transfer dynamic of the photocatalytic process in the presence of the hole acceptors was examined by time-resolved photoluminescence and in situ electron paramagnetic resonance studies.