RESUMEN
Fabricating highly efficient and long-life redox bifunctional electrocatalysts is vital for oxygen-related renewable energy devices. To boost the bifunctional catalytic activity of Fe-N-C single-atom catalysts, it is imperative to fine-tune the coordination microenvironment of the Fe sites to optimize the adsorption/desorption energies of intermediates during oxygen reduction/evolution reactions (ORR/OER) and simultaneously avoid the aggregation of atomically dispersed metal sites. Herein, a strategy is developed for fabricating a free-standing electrocatalyst with atomically dispersed Fe sites (≈0.89 wt.%) supported on N, F, and S ternary-doped hollow carbon nanofibers (FeN4 -NFS-CNF). Both experimental and theoretical findings suggest that the incorporation of ternary heteroatoms modifies the charge distribution of Fe active centers and enhances defect density, thereby optimizing the bifunctional catalytic activities. The efficient regulation isolated Fe centers come from the dual confinement of zeolitic imidazole framework-8 (ZIF-8) and polymerized ionic liquid (PIL), while the precise formation of distinct hierarchical three-dimensional porous structure maximizes the exposure of low-doping Fe active sites and enriched heteroatoms. FeN4 -NFS-CNF achieves remarkable electrocatalytic activity with a high ORR half-wave potential (0.90 V) and a low OER overpotential (270 mV) in alkaline electrolyte, revealing the benefit of optimizing the microenvironment of low-doping iron single atoms in directing bifunctional catalytic activity.
RESUMEN
Herein, we demonstrate that the potential difference of proton reduction and hydrogen gas oxidation of protic ionic liquids is closely related to the proton exchange rate in the electrolyte. Through a careful design of anion chemistry, the proton exchange rate can be boosted by several orders of magnitude, reaching 200 kHz at 100 °C. It is found that the enhanced proton exchange rate can effectively decrease the potential loss at the electrode, most likely through alleviating the H+ concentration gradient incurred by electrochemical reactions at the electrode surfaces. This research therefore highlights the strategy of using anions of medium-strength acids, such as H2PO4-, for protic ionic liquids with enhanced proton exchange capability.
RESUMEN
Organic ionic plastic crystals (OIPCs) are an emerging family of materials with demonstrated applications in electrochemical devices such as lithium/sodium ion batteries, dye-sensitized solar cells, and hydrogen fuel cells. Herein, we present direct evidence of anion diffusion through a relatively static background of a cation lattice in an ionic plastic crystal compound, [P122i4][PF6], in an elevated temperature solid phase. We found all anions are diffusive, whereas only a small population of cations is diffusive. Two anion populations were identified with diffusion coefficients differing by 2 orders of magnitude. The slow-diffusing anion is attributed to the plastic crystal region where the cation forms a relative static background, allowing anions to diffuse possibly through a defect-assisted hopping mechanism.
RESUMEN
Various two-dimensional (2D) side-chain-substituted benzo(1,2-b:4,5-b')dithiophene (BDT) blocks have been used to construct donor polymers, whereas the size effect of the side chains on the photovoltaic performance was overlooked in the past few years. In this work, three size-varied conjugated spaces (benzene, naphthalene, and biphenyl) were introduced into the corresponding polymers PBDB-Ph, PBDB-Na, and PBDB-BPh. This space engineering has a significant impact on the extent of phase separation in the active layer which blended with the polymer and the acceptor ITCPTC and preserved the desired morphology. The varied space size in the side chains lead to distinct balance mobility ratios of holes to electrons (benzene, 0.21; naphthalene, 0.75; and biphenyl, 0.57). Finally, PBDB-Na-based polymer solar cells (PSCs) delivered the highest power conversion efficiency of 12.52% when compared to the PSC performances of PBDB-Ph (8.48%) and PBDB-BPh (11.35%). The method in tailoring the side chain structures could fabricate a balance between phase separation and charge transport, providing an enlightenment for the development of photovoltaic devices.
RESUMEN
Fluorination is a promising modification method to adjust the photophysical profiles of organic semiconductors. Notably, the fluorine modification on donor or acceptor materials could impact the molecular interaction, which is strongly related to the morphology of bulk heterojunction (BHJ) blends and the resultant device performance. Therefore, it is essential to investigate how the molecular interaction affects the morphology of BHJ films. In this study, a new fluorinated polymer PBDB-PSF is synthesized to investigate the molecular interaction in both nonfluorinated (ITIC) and fluorinated (IT-4F) systems. The results reveal that the F-F interaction in the PBDB-PSF:IT-4F system could effectively induce the crystallization of IT-4F while retaining the ideal phase separation scale, resulting in outstanding charge transport. On the contrary, poor morphology can be observed in the PBDB-PSF:ITIC system because of the unbalanced molecular interaction. As a consequence, the PBDB-PSF:IT-4F device delivers an excellent power conversion efficiency of 13.63%, which greatly exceeds that of the PBDB-PSF:ITIC device (9.84%). These results highlight manipulating the micromorphology with regard to molecular interaction.
RESUMEN
In this work, position effects of an alkylthio side chain were investigated by designing and synthesizing two copolymers based on a phenyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDTP) and difluorobenzotriazole (FTAZ). The polymer based on the meta-position-alkylthiolated BDTP, named m-PBDTPS-FTAZ, showed a relatively broader bandgap (2.00 vs 1.96 eV) and lower highest occupied molecular orbital (HOMO) energy level (-5.40 vs -5.32 eV) than its para-positioned structural isomeric analogue polymer (named p-PBDTPS-FTAZ), that is, m- and p-PBDTPS-FTAZ with the side chain structured as ethylhexyl- in the phenyl unit and hexyldecyl- in the FTAZ moiety. When blended with ITIC, m-PBDTPS-FTAZ showed a comparable crystallinity but more uniform morphology compared to that of p-PBDTPS-FTAZ. A high power conversion efficiency of 13.16% was achieved for m-PBDTPS-FTAZ:ITIC devices with a high open circuit voltage (VOC) of 0.95 V, which is higher than that of p-PBDTPS-FTAZ:ITIC devices (10.86%) with a VOC of 0.89 V. Therefore, m-BDTPS could be an effective donor unit to construct high-efficiency polymers due to its effectively decreased HOMO energy level of polymers while still maintaining good molecular stacking.
RESUMEN
In this work, we have reported a highly efficient photovoltaic material, PBDTTz-SBP, by fine-tuning the side chains of the benzodithiophene (BDT) unit. With the replacement of alkoxy chains with alkylthio chains, a large increase in power conversion efficiency (PCE) was realized. Non-fullerene polymer solar cells (PSCs) without any post-treatment generate an optimal PCE of up to 12.09%, with a high VOC of 0.914 V, JSC of 18.52 mA cm-2, and fill factor of 71.43%. Notably, the efficiency of a PBDTTz-SBP-based solar cell was about 1.31-fold of the PCE (9.20%) of its counterpart based on the polymer, PBDTTz-BP, with alkoxy chains, indicating the striking modulation effect of side-chain engineering. Although VOC and JSC were lower than those of non-fullerene devices, the PSCs with PC71BM as the acceptor exhibited a fairly high fill factor of up to 76.69%, affording a moderate PCE. Our work reported a highly efficient polymer solar cell with a PCE of 12.09% and clearly demonstrated the great tuning effect of alkylthio chains on photovoltaic performance.