16 Search Results

Semiconducting polymers are being explored for electrochemical and photoelectrochemical energy transformation and storage applications. For these applications, it is critical to understand how ion insertion from the electrolyte into polymer electrodes modulates the polymer electronic structure and electron doping levels. Here, this study explores electrochemical cation insertion in the n-type conjugated redox polymer P90, composed of alternating naphthalene diimide (NDI) acceptor and bithiophene (T2) donor units, where the NDI units are functionalized with heptaethylene glycol (HEG, 90%) and 2-octyl dodecyl (OD, 10%) side chains. By combining in situ techniques (UV-vis absorption and Raman spectroscopies with electrochemistry), structural analysis using exmore » situ grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) calculations, we reveal that dications enable negative polaron and bipolaron formation in the P90 at less reducing potentials while supporting more bipolaron formation than the monocations; moreover, larger dications with smaller hydrated radii increase the maximum P90 electron doping level. We also determine that the monocations lead to more thermodynamically stabilized polarons compared with the dications. These findings highlight the critical role of cation identity in tuning electrochemical charging, charge stabilization, and electronic structure of n-type conjugated redox polymers, providing guidance on the rational design of polymer-based (photo)electrochemical applications.« less

Photoelectrochemical (PEC) carbon dioxide reduction reaction (CO₂RR) has been considered as a promising route to convert and store solar energy into chemical fuels. It is crucial to find suitable photoelectrode materials that are photo-catalytically active and exhibit excellent photochemical stability. One of the promising contenders is ZnTe with the ∼2.26 eV band gap and prolonged stability under CO₂RR PEC conditions. Herein, a new telluride based thin-film ZnGa₂Te₄ photocathode with lower band gap and stronger visible light absorption compared to ZnTe is synthesized and characterized using a combinatorial sputtering technique. A two-step annealing method with excess Te supply is implemented tomore » synthesize nearly stoichiometric ZnGa₂Te₄ absorber material with a zincblende-derived tetragonal crystal structure confirmed by synchrotron X-ray and electron diffraction. Theoretical calculations show that ZnGa₂Te₄ has suitable direct bandgap (∼1.86 eV) and high absorption coefficient ∼10⁵ cm⁻¹, in agreement with experimentally prepared films. Transient absorption spectroscopy reveals the biexponential decay dynamics, with time constants, τ₁ ∼ 0.04, and τ₂ ∼ 0.65 μs in microsecond time scales and provides the optical transition pathways for this semiconductor thin film. PEC measurements show that the ZnGa₂Te₄ photocurrent densities are comparable to the widely investigated ZnTe photocathodes or even surpass it under simulated sunlight condition. ZnGa₂Te₄ samples demonstrate promising photoelectrochemical stability, maintaining consistent performance under illumination. The inclusion of diaryliodonium additive substantially increases its CO₂RR selectivity to ∼60%. These findings open a new avenue for the synthesis of telluride-based thin-film photocathodes for further exploration and will motivate future research to integrate this potential photocathode material into PEC devices.« less

Colloidal organic nanoparticles (oNPs) have emerged as a promising category of photocatalyst, thanks to their long-lived surface-bound charges, electronic tunability, and strong absorption in the visible spectrum. Our previous research has established a direct correlation between charge generation in oNPs and their photocatalytic activity, highlighting their effectiveness as a framework for stable, long-lived free carriers. However, oNPs have been restricted to use only in aqueous environments as a result of being synthesized via either nano-emulsion or nano-precipitation procedures. Herein, we present a method for transferring oNP photocatalysts from water into polar non-aqueous solvents while retaining their long-term colloidal stability. Wemore » observed that the polymer chains in the solvent-transferred oNPs rearrange from a predominantly H-aggregate structure in water to a combination of H- and J-aggregate characteristics in N,N-dimethylformamide, suggesting a dynamic rearrangement in response to the new solvent environment. Importantly, transient absorption and time-resolved microwave conductivity measurements confirm that the solvent-transferred oNPs maintain their ability to generate free charges at an internal heterojunction. This development opens unique opportunities for eventually leveraging light-generated, long-lived electrons and holes in synthetic redox chemistry across diverse solvent environments, a direction that will be explored in future studies.« less

Since its inception, photoelectrochemistry has sought to power the generation of fuels, particularly hydrogen, using energy from sunlight. Efficient and durable photoelectrodes, however, remain elusive. Here we review the current state of the art, focusing our discussion on advances in photoelectrodes made in the past decade. We open by briefly discussing fundamental photoelectrochemical concepts and implications for photoelectrode function. We next review a broad range of semiconductor photoelectrodes broken down by material class (oxides, nitrides, chalcogenides, and mature photovoltaic semiconductors), identifying intrinsic properties and discussing their influence on performance. We then identify innovative in situ and operando techniques to directlymore » probe the photoelectrode|electrolyte interface, enabling direct assessment of structure–property relationships for catalytic surfaces in active reaction environments. We close by considering more complex photoelectrochemical fuel-forming reactions (carbon dioxide and nitrogen reduction, as well as alternative oxidation reactions), where product selectivity imposes additional criteria on electrochemical driving force and photoelectrode architecture. By contextualizing recent literature within a fundamental framework, we seek to provide direction for continued progress toward achieving efficient and stable fuel-forming photoelectrodes.« less

Photoelectrochemical production of fuels requires photoelectrodes that efficiently convert sunlight to electrochemical energy by producing photovoltage and photocurrent and maintain this ability over time under a variety of pH, illumination, and applied bias conditions. Work in the photovoltaic community has demonstrated that interfaces with high charge carrier selectivity provide high photovoltages. This offers a co-design opportunity to create semiconductor photoelectrodes with contact layers that are both carrier-selective and offer protection from degradation in aqueous solutions. In this work, we explored the ternary nitride ZnTiN₂ as an electronselective, protective layer for Si-based photocathodes. We demonstrated that ZnTiN₂ formed a heterojunction withmore » p-type Si that facilitated electron movement toward the ZnTiN₂ surface for light-driven reduction reactions. Across a variety of electrolyte conditions, ZnTiN₂/Si produced an open circuit voltage of ca. 400 mV vs the solution potential, while bare Si produced 220−480 mV vs the solution potential depending on conditions. ZnTiN₂ was also shown to protect Si over 72 h at open circuit in the dark in 0.1 M KHCO₃ aqueous solution at pH 10.5, with a 2.4% loss in open circuit voltage compared to a 17% loss for unprotected Si. A protective effect was also observed under illumination during methyl viologen reduction at pH 3.5 for 21 h, with a 2.5% loss in open circuit voltage observed for ZnTiN₂/Si compared to a 25% loss in open circuit voltage for unprotected Si under the same conditions. Elemental characterization revealed the presence of oxides on the surface of ZnTiN₂ that are consistent with the Pourbaix diagram after photoelectrochemical operation; these oxides appeared to support durability without hindering charge carrier extraction to drive electrochemical work. This work highlights the promise of ZnTiN₂ for durable photoelectrochemical applications.« less

We explore strategies for enhancing the electronic interaction between silicon nanocrystals (Si NCs) and surface-tethered molecular Re electrocatalysts ([Re]) as models for CO₂-reducing photocathodes. Using density functional theory (DFT) combined with electrochemical, spectroscopic, and photocatalytic measurements, we determine that the intrinsic Si (ⁱSi) NC conduction band energy in ⁱSi-[Re] assemblies is below the [Re] lowest unoccupied molecular orbital (LUMO) and singly occupied molecular orbital energies even for strongly quantum-confined 3.0-3.9 nm diameter hydrogen- and methyl-terminated ⁱSi NCs, respectively. We computationally analyze design strategies to align the semiconductor conduction band edge and electrocatalyst frontier molecular orbitals by varying the ⁱSi NCmore » size, introducing boron as a dopant in the Si NC, and modifying the attachment chemistry to the [Re] complex aryl ligand framework. Our DFT analysis identifies a target hybrid structure featuring B-doped silicon (B:Si) NCs and a direct bond between a surface atom and an sp²-hybridized carbon of the electrocatalyst bipyridine aryl ring ligand (B:Si-C_Ar[Re]). We synthesize the B:Si-C_Ar[Re] NC assembly and find evidence of direct hybridization between the B:Si NC and the surface [Re] electrocatalyst LUMO using electrochemical measurements and transient absorption spectroscopy. This work provides a blueprint for the design of new Si photocathode-molecular electrocatalyst hybrids for CO₂ reduction and related fuel-forming photocatalytic conversions.« less

Ambient temperature growth on Si produces a polycrystalline ZnTiN ₂ film while Sn-assisted growth on sapphire at elevated temperature results in a single-crystal-like ZnTiN ₂ film with significantly reduced sub-bandgap absorption.