Ligand-mediated exciton dissociation and interparticle energy transfer on CsPbBr3 perovskite quantum dots for efficient CO2-to-CO photoreduction

Perovskite quantum dots (PQDs) hold immense potential as photocatalysts for CO2 reduction due to their remarkable quantum properties, which facilitates the generation of multiple excitons, providing the necessary high-energy electrons for CO2 photoreduction. However, harnessing multi-excitons in PQDs for superior photocatalysis remains challenging, as achieving the concurrent dissociation of excitons and interparticle energy transfer proves elusive. This study introduces a ligand density-controlled strategy to enhance both exciton dissociation and interparticle energy transfer in CsPbBr3 PQDs. Optimized CsPbBr3 PQDs with the regulated ligand density exhibit efficient photocatalytic conversion of CO2 to CO, achieving a 2.26-fold improvement over unoptimized counterparts while maintaining chemical integrity. Multiple analytical techniques, including Kelvin probe force microscopy, temperature-dependent photoluminescence, femtosecond transient absorption spectroscopy, and density functional theory calculations, collectively affirm that the proper ligand termination promotes the charge separation and the interparticle transfer through ligand-mediated interfacial electron coupling and electronic interactions. This work reveals ligand density-dependent variations in the gas-solid photocatalytic CO2 reduction performance of CsPbBr3 PQDs, underscoring the importance of ligand engineering for enhancing quantum dot photocatalysis.

Large-scale surface hopping simulation of charge transport in hexagonal molecular crystals: role of electronic coupling signs

In large-scale surface hopping simulations with a huge number of electronic states, trivial crossings could easily lead to incorrect long-range charge transfer and induce large numerical errors. We here study the charge transport in two-dimensional hexagonal molecular crystals with a parameter-free full crossing corrected global flux surface hopping method. Fast time-step size convergence and system size independence have been realized in large systems containing thousands of molecular sites. In hexagonal systems, each molecular site has six nearest neighbours. We find that the signs of their electronic couplings have a strong impact on the charge mobility and delocalization strength. In particular, changing the signs of electronic couplings can even lead to a transition from hopping to band-like transport. In comparison, such phenomena cannot be observed in extensively studied two-dimensional square systems. This is attributed to symmetry of the electronic Hamiltonian and distribu-tion of the energy levels. Due to its high performance, the proposed approach is promising to be applied to more realistic and complex systems for molecular design.

In-situ decoration of tin sulfide on Niobium carbide MXene with robust electronic coupling for improved sodium storage performance

Tin sulfide (SnS) has been considered as one of the most promising sodium storage materials because of its excellent electrochemical activity, low cost, and low-dimensional structure. However, owing to the serious volume change upon discharging/charging and poor electronic conductivity, the SnS-based electrodes often suffer from electrode pulverization and sluggish reaction kinetics, thus resulting in serious capacity fading and degraded rate capability. In this work, SnS nanoparticles uniformly distributed on the surface of the layered Niobium carbide MXene (SnS/Nb₂CT_x) were fabricated through a facile solvothermal approach followed by calcination, endowing the SnS/Nb₂CT_x with a three-dimensional interconnected framework as well as fast charge transfer. Benefitting from the excellent electronic/ionic conductivity, efficient buffering matrix, abundant active sites, and high sodium storage activity inherited from the structure design, the robust electronic coupling between SnS nanoparticle and Nb₂CT_x MXene results in excellent electrochemical output, which demonstrates superior reversible capacities of 479.6 (0.1 A/g up to 100 cycles) and 278.9 mAh/g (0.5 A/g up to 500 cycles) upon sodium storage, respectively. The excellent electrochemical performance manifests the promise of the combination of metal sulfides with Nb₂CT_x MXene to fabricate high-performance electrodes for sodium storage.

The role of various components in Ru-NiCo alloys in boosting the performance of overall water splitting

Understanding the synergistic mechanism of multi-component alloys is crucial and challenging for overall water splitting. Herein, Ru-NiCo_0.5-600 °C and Ru-Ni_0.75Co with excellent electrocatalytic activity are designed and synthesized. The Ru-NiCo_0.5-600 °C alloy exhibits remarkable HER activity with an overpotential of 42, 77 and 93 mV at 10 mA cm^-2 in alkaline, acidic and neutral conditions, and the Ru-Ni_0.75Co electrocatalyst presents outstanding OER activity with an overpotential of 176 mV at 10 mA cm^-2 in 1.0 M KOH. The Ru-NiCo_0.5-600 °C ||Ru-Ni_0.75Co cell requires only 1.48 and 1.69 V to reach 10 and 100 mA cm^-2 towards overall water splitting. A series of experiments reveal that the strong electronic coupling among Ru, Ni and Co regulates the electronic structure and enhances the intrinsic catalytic activity and stability of the as-synthesized Ru-NiCo electrocatalysts. Systematic experimental and theoretical results prove that Ni atoms act as the active sites of dissociating water, while Ru and Co are respectively the active centers of proton and hydroxyl adsorption for HER and OER. Our work provides a new perspective for profoundly understanding the synergistic effect of multi-component alloys towards water splitting.

Sodium titanium phosphate nanocube decorated on tablet-like carbon for robust sodium storage performance at low temperature

Sodium-ion batteries, featuring resource abundance and similar working mechanisms to lithium-ion batteries, have gained extensive interest in both scientific exploration and industrial applications. However, the extremely sluggish reaction kinetics of charge carrier (Na+) at subzero temperatures significantly reduces their specific capacities and cycling life. Herein, this study presents a novel hybrid structure with sodium titanium phosphate (NaTi2(PO4)3, NTP) nanocube in-situ decorated on tablet-like carbon (NTP/C), which manifests superior sodium storage performances at low temperatures. At even -25 °C, a stable cycling with a specific capacity of 94.3 mAh/g can still be maintained after 200 cycles at 0.5 A/g, delivering a high capacity retention of 91.5 % compared with that at room temperature, along with an excellent rate capability. Generally, the superionic conductor structure, flat voltage plateaus, as well as the conductive carbonaceous framework can efficiently facilitate the charge transfer, accelerate the diffusion of Na+, and decrease the electrochemical polarization. Moreover, further investigations on diffusion kinetics, solid electrolyte interface layer, and the interaction between NTP and carbonaceous skeleton reveal its high Na+ diffusion coefficient, robust solid electrolyte interface, and strong electronic interaction, thus contributing to the superior capacity retentions at subzero temperatures.

Atomic heterojunction-induced accelerated charge transfer for boosted photocatalytic hydrogen evolution over 1D CdS nanorod/2D ZnIn2S4 nanosheet composites

Design of highly efficient heterojunctions for photocatalytic hydrogen evolution is of significant importance to address the energy shortage and environmental crisis. Nevertheless, the smart design of semiconductor-based heterojunctions at the atomic scale still remains a significant challenge hitherto. Herein, we report novel atomic CdS/ZnIn₂S₄ heterojunctions by in-situ epitaxially growing 2D ZnIn₂S₄ nanosheets onto the surface of 1D defective CdS nanorods. The strong electronic coupling between defective CdS and ZnIn₂S₄ is confirmed by transient photocurrent response measurements, •O₂^- and •OH radicals experiments, and PL results, leading to accelerated interfacial charge separation and transfer. Additionally, the elevated charge transfer and electronic coupling are further confirmed by theoretical calculations. Consequently, CdS/ZnIn₂S₄ hybrids exhibit superior photocatalytic hydrogen generation activity to pristine CdS. Our findings offer a new paradigm for designing atomic 1D/2D heterojunctions for efficient solar-driven energy conversion.

Effects of co-adsorption on interfacial charge transfer in a quantum dot@dye composite

The sensitive electronic environment at the quantum dot (QD)-dye interface becomes a roadblock to enhancing the energy conversion efficiency of dye-functionalized quantum dots (QDs). Energy alignments and electronic couplings are the critical factors governing the directions and rates of different charge transfer pathways at the interface, which are tunable by changing the specific linkage groups that connect a dye to the QD surface. The variation of specific anchors changes the binding configurations of a dye on the QD surface. In addition, the presence of a co-adsorbent changes the dipole-dipole and electronic interactions between a QD and a dye, resulting in different electronic environments at the interface. In the present work, we performed density functional theory (DFT)-based calculations to study the different binding configurations of N719 dye on the surface of a Cd₃₃Se₃₃ QD with a co-adsorbent D131 dye. The results revealed that the electronic couplings for electron transfer were greater than for hole transfer when the structure involved isocyanate groups as anchors. Such strong electronic couplings significantly stabilize the occupied states of the dye, pushing them deep inside the valence band of the QD and making hole transfer in these structures thermodynamically unfavourable. When carboxylates were involved as anchors, the electronic couplings for hole transfer were comparable to electron transfer, implying efficient charge separation at the QD-dye interface and reduced electron-hole recombination within the QD. We also found that the electronic couplings for electron transfer were larger than those for back electron transfer, suggesting efficient charge separation in photoexcited QDs. Overall, the current computational study reveals some fundamental aspects of the relationship between the interfacial charge transfer for QD@dye composites and their morphologies which benefit the design of QD-based nanomaterials for photovoltaic applications.

Electronic coupling between molybdenum disulfide and gold nanoparticles to enhance the peroxidase activity for the colorimetric immunoassays of hydrogen peroxide and cancer cells

Peroxidase nanoenzymes exhibit a specific affinity toward substrates, thereby demonstrating application potential for realizing the colorimetric immunoassays of hydrogen peroxide (H₂O₂), which can be further used as a probe for imaging cancer cells. To enhance the intrinsic peroxidase activity of molybdenum sulfide (MoS₂) nanomaterials, gold (Au) nanoparticles with an average diameter of approximately 2.1 nm were modified on a MoS₂/carbon surface (denoted as MoS₂/C-Au₆₀₀) via ascorbic acid reduction. MoS₂/C-Au₆₀₀ can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate a blue oxidation product in the presence of H₂O₂; this product exhibits peroxidase-like activities, superior to those of most existing MoS₂-based nanoenzymes. Furthermore, MoS₂/C-Au₆₀₀ exhibits a high detection capability for H₂O₂ in the range of 1 × 10^-5 to 2 × 10^-4 mol/L (R² = 0.99), and the lowest detection limit is 1.82 µmol/L in a sodium acetate and acetic acid buffer solution. Steady state kinetics studies indicate that the catalytic mechanism is consistent with the ping-pong mechanism. Given its strong absorption peak at 652 nm in the visible region, MoS₂/C-Au₆₀₀ can be used to image cancer cells due to the enhanced permeability and retention effect. Our findings demonstrate that the synergistic electronic coupling between multiple components can enhance the peroxidase activity, which can facilitate the development of an effective, facile, and reliable method to perform colorimetric immunoassays of H₂O₂ and cancer cells.

Carotenoid dark state to chlorophyll energy transfer in isolated light-harvesting complexes CP24 and CP29

We present a comparison of the energy transfer between carotenoid dark states and chlorophylls for the minor complexes CP24 and CP29. To elucidate the potential involvement of certain carotenoid-chlorophyll coupling sites in fluorescence quenching of distinct complexes, varying carotenoid compositions and mutants lacking chlorophylls at specific binding sites were examined. Energy transfers between carotenoid dark states and chlorophylls were compared using the coupling parameter, [Formula: see text], which is calculated from the chlorophyll fluorescence observed after preferential carotenoid two-photon excitation. In CP24, artificial reconstitution with zeaxanthin leads to a significant reduction in the chlorophyll fluorescence quantum yield, [Formula: see text], and a considerable increase in [Formula: see text]. Similar effects of zeaxanthin were also observed in certain samples of CP29. In CP29, also the replacement of violaxanthin by the sole presence of lutein results in a significant quenching and increased [Formula: see text]. In contrast, the replacement of violaxanthin by lutein in CP24 is not significantly increasing [Formula: see text]. In general, these findings provide evidence that modification of the electronic coupling between carotenoid dark states and chlorophylls by changing carotenoids at distinct sites can significantly influence the quenching of these minor proteins, particularly when zeaxanthin or lutein is used. The absence of Chl612 in CP24 and of Chl612 or Chl603 in CP29 has a considerably smaller effect on [Formula: see text] and [Formula: see text] than the influence of some carotenoids reported above. However, in CP29 our results indicate slightly dequenching and decreased [Formula: see text] when these chlorophylls are absent. This might indicate that both, Chl612 and Chl603 are involved in carotenoid-dependent quenching in isolated CP29.

Rational design of D-π-A organic dyes to prevent "trade off" effect in dye-sensitized solar cells

It is an easy task to simulate the spectrum properties for the organic dyes applied in dye-sensitized solar cells (DSSCs) if the suitable method is chosen. However, it is still difficult to quantitatively determine the overall performance for them. In this work, the short-circuit photocurrent density (J_SC) and open circuit photovoltage (V_OC) are quantitatively calculated by combination of the density functional theory and first principle for DSSCs based on four different organic dyes, 2-((4'-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)biphenyl-4-yl)methylene)but-3-ynoic acid (1), 2-((5-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)phenyl)thiophen-2-yl)methylene)but-3-ynoic acid (2), 3-(7-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)-4H-cyclopenta[2,1-b:3,4-b']-dithiophene)-2-cyanoacrylic acid (3), and 3-(7-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)phenyl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-cyanoacrylic acid (4), in which the triarylamine is donor and the cyanoacrylic acid is acceptor along with variable π group. The 3 and 4 are new theoretically designed organic dyes on the basis of 1 and 2 with different electron-rich group as π group. Both J_SC and V_OC of 3 and 4 are improved as compared with those of 1 and 2, which breaks the normal "trade-off" rule. As a result, the power conversion efficiency (PCE) of 3 and 4 is improved, especially for 3. The aggregation effect is also considered to evaluate the overall performance, which is favorable to further enhance the reliability of theoretical design.

A theoretical multiscale treatment of protein-protein electron transfer: The ferredoxin/ferredoxin-NADP(+) reductase and flavodoxin/ferredoxin-NADP(+) reductase systems

In the photosynthetic electron transfer (ET) chain, two electrons transfer from photosystem I to the flavin-dependent ferredoxin-NADP(+) reductase (FNR) via two sequential independent ferredoxin (Fd) electron carriers. In some algae and cyanobacteria (as Anabaena), under low iron conditions, flavodoxin (Fld) replaces Fd as single electron carrier. Extensive mutational studies have characterized the protein-protein interaction in FNR/Fd and FNR/Fld complexes. Interestingly, even though Fd and Fld share the interaction site on FNR, individual residues on FNR do not participate to the same extent in the interaction with each of the protein partners, pointing to different electron transfer mechanisms. Despite of extensive mutational studies, only FNR/Fd X-ray structures from Anabaena and maize have been solved; structural data for FNR/Fld remains elusive. Here, we present a multiscale modelling approach including coarse-grained and all-atom protein-protein docking, the QM/MM e-Pathway analysis and electronic coupling calculations, allowing for a molecular and electronic comprehensive analysis of the ET process in both complexes. Our results, consistent with experimental mutational data, reveal the ET in FNR/Fd proceeding through a bridge-mediated mechanism in a dominant protein-protein complex, where transfer of the electron is facilitated by Fd loop-residues 40-49. In FNR/Fld, however, we observe a direct transfer between redox cofactors and less complex specificity than in Fd; more than one orientation in the encounter complex can be efficient in ET.

Mechanisms for control of biological electron transfer reactions

Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions.