Probing the dynamics of molecular catalysts at electrode-electrolyte interfaces is essential for understanding catalytic mechanisms. Structure-specific spectroscopic methods are particularly powerful for examining electrocatalytic interfaces but are mostly used under steady-state conditions. Herein, we combined surface-enhanced infrared absorption spectroscopy (SEIRAS) with phase-sensitive detection (PSD) to investigate the dynamics of a molecular Ir-based water oxidation catalyst at the Au-electrolyte interface. We found that the amplitude of the absorbance of the catalyst is anticorrelated to that of interfacial water. This anticorrelation can be understood by the adsorption of the electrooxidized catalyst on the electrode and concurrent displacement of interfacial water. The infrared signals from the interface exhibit an increasing phase lag with respect to the electrode potential with an increasing scan rate of the potential. Kinetic modeling suggests that the potential-dependent adsorption-desorption kinetics of the molecular catalyst on the electrode gives rise to this phase lag. This study shows that PSD-SEIRAS is a powerful tool for investigating the interfacial dynamics of electrocatalytic systems.

Triphenylene (TP) based 2-dimensional (2D) metal-organic frameworks (MOFs) have attracted growing interest as photoconductive materials for sensing, photo(electro)catalysis, energy storage, and optoelectronic applications. However, the fundamental understanding of the factors that govern charge transport mechanisms in these materials remains poorly understood. In this work, we combine multiple spectroscopic techniques, including steady state X-ray absorption and UV-Visible-NIR absorption spectroscopy, transient absorption spectroscopy, and first-principles calculations, to examine the origins of charge transport behaviors in hexahydroxytriphenylene (HHTP) based MOFs. We found that the metal-to-ligand charge-transfer band is governed by the identity of the metal node, highlighting the important role of metal-ligand d-π interactions, whereas the near-infrared absorption band depends strongly on film thickness, reflecting the contribution of interlayer π-π interactions. Our findings identify two distinct strategies for tuning charge transport mechanisms in these emerging materials and provide new mechanistic insights to guide the rational design of HHTP-based MOFs for practical device applications.

The direct and selective oxidation of light alkanes into value-added liquid chemicals under mild conditions remains a long-standing challenge in catalysis. Here, we report a heterogeneous photocatalyst based on site-isolated decatungstate (DT) anions immobilized on SBA-15 via a silatrane linker (sil-DT). Under UV-light irradiation at room temperature and ambient pressure, the catalyst selectively oxidizes propane to acetone and exhibits an acetone production rate of 11.2 mmol gDT-1 h-1 , a total liquid product selectivity of 89.0%, and an acetone fraction of 69.0% within the liquid products. In contrast, bulk sodium DT (NaDT) shows negligible activity under identical conditions. Spectroscopic and computational studies reveal that the high catalytic performance arises from the uniform dispersion and site isolation of DT species, which retain the photo-physical properties of their homogeneous counterparts. This work demonstrates the critical role of molecular dispersion in enabling selective light-driven alkane oxidation and offers a sustainable route for propane valorization.

Polyolefins are ubiquitous in consumer products but are notoriously difficult to recycle due to the inherent incompatibility of their common varieties. Current approaches to addressing this challenge often involve relatively complex syntheses or may compromise the properties of the parent materials. Here, a method is developed to compatibilize mixed polyolefins via acid-base interactions. With a single-step photocatalytic process, acid or base functionality can be readily installed onto polyolefins. The combination of acid- and base-modified polyolefins functions as a compatibilizers. Incorporating them into polyolefin blends results in excellent mechanical strength, with up to a 96-fold increase in ductility (from 22% to 2110%). Importantly, compatibilization can be readily achieved on postconsumer polyolefin mixtures. Furthermore, direct functionalization and compatibilization of polyolefin blends is achieved.

Light-driven catalytic reactions such as solar water splitting rely on photogenerated charges to promote chemical reactions that are otherwise difficult or impossible to take place. By nature, this type of reactions proceeds through cascading steps that include charge generation, transfer, and charge-neutral chemical processes. The involvement of photogenerated charges is a key feature that distinguishes photocatalytic chemical reactions from other similar reactions such as electrocatalytic ones. The synergistic effect between the rate at which photocharges are generated and the kinetics of the chemical steps is expected to be of critical importance but has received relatively little attention. In this talk, we will present our recent efforts aimed at filling in this knowledge gap. Using photoelectrochemical water oxidation as a prototypical reaction, we examined how the overall reaction rate depends on both the surface hole concentration and the catalytically active site density. A cooperative behavior among adjacent active sties was observed. The nature of the chemical steps was also found to influence the photophysical behaviors of charges within the light absorber itself. These results highlight the importance to regard the photocatalytic systems as an integrated system. They further inspire us to examine the detailed processes at the molecular level.

Solar-driven water splitting requires sufficient photovoltage to drive both water oxidation and proton reduction. Understanding the factors driving and limiting photovoltage generation is therefore crucial to optimizing photoelectrode design but has proven challenging to determine under operando conditions for photoanodes driving slow multiredox reactions such as water oxidation. In this work, operando optical spectroscopy is employed to measure the hole quasi-Fermi level (EF,p) position in model hematite photoanodes as a function of applied bias and light intensity. The quasi-Fermi level splitting determined from these data are shown be in excellent agreement with the directly measured photovoltages, demonstrating the primarily electrochemical rather than primarily electrostatic origin of photovoltage in these photoelectrodes. EF,p pinning is observed at low light intensities and biases, indicative of hole trap states lying ∼0.2 eV above the valence band edge with a density of ∼1 nm-2. Hole accumulation in these trap states is correlated with first order water oxidation. At higher light intensities and/or more anodic bias, EF,p becomes unpinned, assigned to saturation of these trap states, and correlated with the onset of third order water oxidation to molecular oxygen. Comparison with rate law analyses for other photoanodes indicates that such hole trap states may be a ubiquitous feature of metal oxides and suggests that materials processing strategies to suppress the density of such states would be a promising strategy to enhance photoanode performance.

Water oxidation holds the key to the goal of harvesting and storing solar energy in chemical bonds. This is because the reaction liberates electrons and protons from water, the only sacrificial reagent abundant enough to meet the terawatts scale need for solar fuel synthesis. Due to the high oxidizing power required to oxidize water, however, it has been exceedingly difficult to carry out this reaction using catalysts that are efficient, durable, and inexpensive at the same time. An important reason for the challenge is the lack of understanding of the reaction, especially at the molecular level. In this presentation, we will share our latest efforts and advances in this direction. Specifically, we will show our results in studying the temperature effect on photoelectrochemical (PEC) water oxidation. In the past, it has been assumed that the chemical steps of a PEC water oxidation process are the limiting factors, and raising reaction temperature is expected to accelerate the chemical steps and, hence, the overall water oxidation performance. Our experiments revealed an inverse temperature dependence for hematite-based photoelectrodes, however. It was rationalized that the effect was reporting on the chemical nature of the overall catalytic cycle for water oxidation. On hematite, the early steps in the catalytic cycle are slow. As a result, holes stored in the intermediates are more likely to back-transfer for recombination with surface electrons. Our results shed light on the complexities of PEC reactions that involve multiple electrons and multiple protons. Future research of the system should treat the overall process synergistically in order to develop a holistic view, which will play key roles in advancing our search for desired catalysts.

The oxidation of water to molecular oxygen, referred to as the oxygen evolution reaction (OER), is often the kinetic bottleneck in the formation of renewable fuels. The rate of the OER is strongly dependent on electrolyte properties, such as pH, ionic strength, and the identities of anions and cations. To advance OER catalysis, it is essential to understand the mechanisms by which the electrolyte influences the rate of the OER. In this article, we discuss recent work concerned with the effects of electrolyte cations on the OER. We examine how cations modulate apparent Arrhenius parameters, their effects on the interfacial water structure, their direct interactions with intermediates, and how they alter the rate through non-kinetic effects. The survey reveals that cations can influence the OER through a diversity of mechanisms and that their effects strongly depend on catalyst composition and reaction conditions.

The continuous demand for lithium-ion batteries (LIBs) in consumer products and electric vehicles (EVs) has raised concerns about their environmental impact when not disposed of properly. Among the components of a spent LIB, the recovery of heavy metals such as Nickel, Manganese, and Cobalt from the cathode materials is the most critical. While this goal can be achieved through processes such as biohydrometallurgy, it relies on large quantities of chemicals such as FeSO4 for the energy source, which can limit the scalability. In this work, we seek to develop a modified biohydrometallurgy process that is self-sufficient. For this purpose, we examined the feasibility of replacing FeSO4 salt with metallic Fe, which is readily available and abundant in spent batteries as protective cases. The growth profile of the autotrophic bacterium Acidithiobacillus ferrooxidans (Atf) was studied after the initial acidification with H2SO4 or HCl. The resulting culture was then used to leach model cathode materials made of NMC622 (Ni:Mn:Co=6:2:2). Near-unity leaching efficiencies were measured on all four elements of interest, Li, Ni, Mn, and Co, when compared with those by aqua regia based digestion. This new bioleaching process opens the door to efficiently recovering cathode metals while further simplifying the cultivation process, promising scaled up applications.

Water oxidation is an important reaction to provide electrons and protons that are essential for fuel forming reactions such as hydrogen generation and carbon dioxide reduction. For thermodynamic and kinetic reasons, this reaction remains a critical challenge. Due to its multi-charge nature, the reaction is also a good study platform to understand the effects of various factors on complex electrochemical reactions. While there have been extensive research on the structure-property relationship of water oxidation catalysts, the impacts of the electrolyte on the reaction have received relatively little attention. In this talk, we will present a summary of existing literatures on how water oxidation reaction is influenced by the composition of the electrolyte. Based on this discussion, we will report our own results on how a simple Langmuir adsorption model can be used to explain seemingly complex behaviors of the electrolyte. We will show that the kinetics of water oxidation is not influenced by the anions but also the cations. The results will likely find broad implications in practical electrochemical applications.

Multicarbon (Cn, where n ≥ 2) oxygenates are important industrial precursors that can be synthesized from the coupling of simple and abundant C1 feedstock such as CH4. While C2 products from this route have been reported, those involving the direct coupling of more than two C1 precursors are rare. As a proof of concept, here we report the synthesis of acetone (CH3COCH3) through the direct coupling of two CH4 and one CO using a combined photothermocatalytic approach. With TiO2 as a light absorber and Pd nanoparticle as a cocatalyst, CH4 activation and subsequent coupling with CO were achieved at 10 bar and 150 °C. A high selectivity of acetone formation among all liquid products (>80%) was measured. Experiments with isotope-labeled precursors confirmed that the product was a result of the direct coupling of CH4 and CO. The other major liquid product was acetic acid (CH3COOH), which was a result of a single coupling between CH4 and CO. The suitable binding strength between Pd and the reactive intermediates was proposed as a key reason for the high selectivity toward C3 products.

The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, systematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrOx. The results show that nitrate can suppress the reaction, resulting in a decrease in the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reaction intermediates and nitrate, suggesting that the reaction mechanism was unaffected by the anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend of Li+ approximate to Na+ approximate to K+ > Cs+ > TEA(+). The results are expected to have broad applications in electrocatalysis.

Semiconductor photoelectrochemistry is a dynamic and interdisciplinary field at the forefront of research in solar fuels, energy conversion, and catalysis. This Perspective captures the collective insights from the second Gerischer Electrochemistry Today Symposium, held at Colorado State University in Fort Collins, CO, in August 2024, which convened leading researchers, early-career scientists, and industry partners to define the critical next steps for the field. Through interactive sessions, technical talks, panel discussions, and training initiatives-including a Semiconductor Electrochemistry Bootcamp-the symposium emphasized three pillars of advancement: (i) facilitating the exchange of new ideas in semiconductor electrochemistry and charge separation; (ii) fostering the development of future researchers, research topics, and participation in the semiconductor workforce; and (iii) building community. This Energy Focus distills key themes from the meeting and identifies major knowledge gaps in the following areas: mechanisms of charge separation and recombination, role of defects and disorder, dynamic and operando characterization methods, interfacial chemistry and surface passivation, theoretical and modeling limitations, and standardization and benchmarking. The inclusive and collaborative structure of the symposium enabled the generation of this comprehensive report that will serve as a roadmap for fundamental and applied research in the rapidly evolving field of semiconductor electrochemistry over the next decade.

A simple electrochemical method and dip-coating method were both used to synthesize novel heterostructures based on copper oxide/bismuth molybdate (CuO/Bi2MoO6) thin films on fluorine-doped tin oxide (FTO) substrate. The semiconductor electrode was thoroughly characterized by XRD, photoluminescence, XPS, SEM, EDS, voltammetry and chronoamperometry. Diffuse reflectance UV-Vis was measured as well as determined the optical bandgap energies. The p- and n-type semiconductor characteristics of CuO and Bi2MoO6, respectively, were elucidated via Mott-Schottky analysis. This analysis also facilitated the determination of their flat-band potentials, enabling the construction of the energy band alignment consistent with an efficient direct Z-scheme heterostructure. A highest ciprofloxacin removal efficiency of 83.7% was achieved via photoelectrocatalytic treatment using Het, wherein singlet oxygen was identified as the predominant oxidizing species, playing a primary role in the initiation and acceleration of the ciprofloxacin molecular degradation. The ciprofloxacin degradation involves three pathways through cleavage of carbon-fluorine bonds, oxidation of the piperazine ring and the decarbonylation reactions as indicated by chromatographic analysis of the degradation products. This electrode provides valuable insights into the advancement of environmentally sustainable technologies for water treatment and pharmaceutical remediation.

The versatility of using electrodes to control catalytic reactions heralds a new paradigm in designing chemical transformations based on molecular compounds. Functionalization of molecular compounds on an electrically addressable surface offers an additional degree of freedom in controlling a catalyst’s reactivity and selectivity. Herein, we discuss the possibilities to harness electrode-supported molecular catalysts in electrocatalytic reactions and electrostatic effects observed in the surface-anchored systems recently reported. Furthermore, we summarize reported functionalization methods and outline how the proximate electrode asserts its influence on catalysis by a variety of avenues.

Although heterogeneous photo-Fenton reactions on nanoparticulate iron oxides effectively degrade organic pollutants, the underlying surface mechanisms remain debated. Here, we demonstrate how these pathways are modulated by specific hematite crystal facets. To investigate the influence of particle surface structure, methylene blue (MB) adsorption and photodegradation kinetics are examined using facet-engineered hematite nanoparticles with distinct exposed facets. The results reveal that MB photodegradation strongly depends on both pH and facet orientation. When normalized by surface area, (116) facet shows higher photodegradation activity than those with (104) or (001) facets. This enhanced activity is attributed to favorable electronic structure and surface characteristics, including a smaller optical bandgap, faster charge transfer, and superior H2O2 decomposition. In contrast, the photodegradation capacity follows (104) 〉 (116) 〉 (001), primarily due to the higher density of surface-active sites on the (104) facet. These sites promote coupled MB adsorption and degradation, enabling removal of a greater overall quantity of MB. Additionally, under high pH conditions, hematite can degrade MB in the dark, with capacities following (001) ≫ (116) 〉 (104). These findings underscore the critical catalytic role of specific hematite surfaces and advance the understanding of facet-dependent photoinduced redox chemistry at mineral-water interfaces.

We applied a classifier method to predict palladium catalysts for the formation of nonalternating polyketones via the copolymerization of CO and ethylene; current examples are limited to using phosphine sulfonate and diphosphazane monoxide supporting ligands. With the reported workflow, we discovered two new classes of palladium complexes capable of achieving the synthesis of nonalternating polyketones with a lower CO content than those made by known palladium catalysts. Our results show that we doubled the number of classes of palladium compounds that can catalyze the formation of this type of polymer. We envision that this methodology can be applied to accelerate catalyst discovery when selectivity is an important outcome.

The inherent instability and low solubility of polysulfides in Mg-based electrolytes contribute to the poor performance of magnesium-sulfur (Mg-S) battery systems. To address these challenges, we utilize a combination of first-principle theory, spectroscopy, and electrochemical measurements to investigate the chemistry of Mg polysulfides. Our study reveals the critical role of polysulfide species present in the battery electrolyte in determining electrochemical stability and performance. Through detailed atomistic-level explorations of polysulfide conformations and their role in Mg-S chemistry, corroborated by experiments, we discover that the disproportionation of long-chain Mg polysulfides into shorter-chain compounds is thermodynamically favored at room temperature. In contrast, multiple polysulfide radical species can form under electrochemical conditions. Meanwhile, the dissociation of Mg2+ from the coordinating polysulfide anions is highly unfavorable regardless of the solvent used. Our theoretical predictions for UV-vis, Raman, and electron paramagnetic resonance (EPR) spectra, which account for the full ensemble of polysulfide conformers and species at thermodynamic equilibrium, align well with experimental data and facilitate reference peak assignments for future in situ studies of Mg-S systems. Furthermore, we separate the electrochemical contributions from the entire conformational ensemble by calculating the reduction potentials for the dominant Mg polysulfide species to clarify the principal redox pathways during the electrochemical cycling of Mg-S batteries. This theoretical electrochemical data is applied to explain key features in the discharge curve of an experimental Mg-S electrochemical cell. Our integrated approach provides important insights into the mechanistic behavior of Mg polysulfides in electrochemical systems. In particular, by dissecting the conformer-dependent thermal and electrochemical reactivities of Mg2+-polysulfide complexes, we enhance the fundamental understanding of their chemistry and establish new foundations for optimizing Mg-S battery design.

In this study, heterostructures based on Bismuth molybdite/iron oxide (Bi2MoO6/Fe2O3) thin films were fabricated by a dip-coating technique using precursor solutions. The heterostructures were deposited on fluorine-doped tin oxide glass substrates. From a detailed characterization using X-ray diffraction and X-ray photoelectron spectroscopy, the formation of the orthorhombic phase for Bi2MoO6 and the co-existence of hematite and maghemite in Fe2O3 was demonstrated. Meanwhile, the field emission scanning electron microscopy cross-section images confirm the formation of well-defined Bi2MoO6 film under the Fe2O3 deposition. The optical band gap energies for the heterostructure obtained were estimated from the diffuse reflectance spectra and ranged from 2.3 to 3.5 eV. Photoluminescence analysis revealed an improved separation and faster transfer of photogenerated electrons and holes for the Bi2MoO6/Fe2O3 (Het) film. The best oxytetracycline (OTC) removal percentage through photoelectrocatalytic treatment was 96.85% using the Het. Besides, were carried out the variation of parameters which affect the OTC photoelectrocatalytic degradation as pH, potential applied, and scavenger assay. The 1O2 was the oxidant predominate, which attack the OTC ring to initiate and accelerate the degradation process. Based on the analysis of degradation intermediates and characteristics of Bi2MoO6/Fe2O3, possible degradation pathways and mechanisms of OTC were displayed. An enhancement of oxytetracycline degradation efficiency of Het fabricated compared to pristine oxides was achieved mainly due to avoid the charge recombination of photogenerated electron-hole pairs provided by Direct Z-scheme heterostructure. Finally, the Het fabricated represents a promising material for efficient and sustainable pharmaceutical removal applications.

Rechargeable Mg batteries are a promising energy storage technology to overcome the limitations inherent to Li ion batteries. A critical challenge in advancing Mg batteries is the lack of suitable cathode materials. In this work, we report a cathode design that incorporates S functionality into two-dimensional metal-organic-frameworks (2D-MOFs). This new cathode material enables good Mg2+ storage capacity and outstanding cyclability. It was found that upon the initial Mg2+ insertion and disinsertion, there is an apparent structural transformation that crumbles the layered 2D framework, leading to amorphization. The resulting material serves as the active material to host Mg2+ through reduction and/or oxidation of S and, to a limited extent, O. The reversible nature of S and O redox chemistry was confirmed by spectroscopic characterizations and validated by density functional calculations. Importantly, during the Mg2+ insertion and disinsertion process, the 2D nature of the framework was maintained, which plays a key role in enabling the high reversibility of the MOF cathode.