In metalloenzymes, precise control of metal-metal distance and coordination environment enables challenging catalytic transformations. This often involves hydrogen bonding in the second coordination sphere. Although many homogeneous systems aim to mimic these features, the capture and characterization of transient coordination events remains a challenge. Exploring the first di-iron complex of the rotationally flexible dinucleating ligand 1,1 ',5,5 ',6,6 '-hexamethyl-4,4 '-bis(picolinimino)-2,2 '-bibenzimidazole, report an unexpected, entropy-driven ligand-exchange equilibrium which we describe by means of variable temperature studies in solution, key species fully structurally characterized in crystallo, and a mechanistic study in silico. This comprehensive experimental and computational characterization of the ligand and complex revealed how the central C-C bond enables adaptation to different metal-metal distances. Cooling a methanol solution of the complex induces a color change from green to blue which is attributed to the reversible substitution of chlorido ligands by methanol. Density functional theory calculations suggest that this ligand exchange is driven by the change in entropy inherent to the reduction of temperature. Under controlled conditions, electrochemical analysis reveals two accessible redox events: a fully reversible redox process at -0.05 V vs Fc/Fc+ and a series of irreversible reduction reactions at more negative potentials. The resemblance of these redox features with those in established iron catalysts highlights the potential of this system to support catalytic transformations under certain conditions.

We demonstrate the feasibility of a process for the direct and easily accessible production of high purity H 2 from seawater with no membrane involved. Green hydrogen production is inherently bound to the use of water electrolyzers, a technology that suffers from the use of highly pure water, with additional costs and loss in the overall energy efficiency, and of polymeric membranes, that are in many cases based on fluorinated compounds. The anodic oxygen evolution reaction is substituted by chlorine evolution reaction. Evolved chlorine rapidly reacts forming hypochlorite ions, that are subsequently decomposed into O 2 and chloride ions in a fixed bed reactor containing a Ni based catalyst. The results show that both on simulated and on real seawater, H 2 purity reaches 98%, and that the final concentration of hypochlorite falls around 0.2 mM (10 ppm). Thanks to the use of two identical Pt oxide electrodes, current reversal avoids the deposition of scale/limestone derived solids at the cathode, thus increasing the robustness of the process.

Ligand systems used for electrochemical reductions commonly comprise single metal centres. This is opposed to complexes with two or more adjacent metals which are significantly less studied. In order to fill this gap a Fe dimer embedded into the 1,1 ',5,5 ',6,6 '-hexamethyl-4,4 '-bis(picolinimino)-2,2 '-bibenzimidazole (Mebpbbi) ligand system is studied in the present work with focus on electrochemical properties in acetonitrile solution. A combination of cyclic voltammetry and density functional theory (DFT) reveals that the complex is present at least as an open, non-bridged, and a closed, (& micro;-Cl)2 bridged complex. Both forms possess very different redox properties and ligand exchange energetics. The presence of a stable reversible electron transfer couple for the non-bridged complex is promising for electrocatalytic reactions. Surprisingly, our calculations demonstrate that the iron ions essentially maintain their charge while the ligand accommodates the charges involved in the different redox steps.

To achieve a sustainable future, the electrification of the chemical manufacturing industry is crucial. The electrochemical CO2 reduction reaction (CO2RR) offers a promising pathway to produce value-added chemicals and fuels, including methanol─a key chemical building block and energy carrier. This approach presents a carbon-neutral alternative to conventional, fossil fuel-based methanol production. However, replacing well-established thermochemical processes and achieving cost-competitive production requires the development of highly efficient and selective catalysts for CO2-to-methanol conversion, as well as systematic device-level optimization. In this Perspective, we discuss the potential of methanol production via CO2RR and provide an overview of recent advances in catalyst development. We also propose experimental protocols for methanol quantification, emphasizing the critical need for rigorous evaluation of catalysts to ensure the validity and reproducibility of results, and demonstrating boron phosphide as an irreproducible case. We review seminal studies on CO2RR by cobalt phthalocyanine to make methanol, and current understanding of the reaction mechanistic details. Lastly, we discuss the challenges associated with its translation into practical devices and outline future research opportunities to advance electrochemical CO2RR for methanol production at scale.

One of the ultimate goals of photocatalysis is the direct utilzation of solar energy into the production of useful chemical products. In particular the direct photocatalytic water splitting to produce molecular hydrogen as a versatile, sustainable and ecologically friendly fuel is of great interest. This goal has motivated numerous research efforts to develop and improve corresponding photochemical molecular devices. However, it is fair to say that most of these efforts concentrated on the identification of the light-driven electron transfer processes within these devices, whereas the mechanistic details of the hydrogen evolution reaction remained largely unexplored. Here we present a first-principles based theoretical study of a photochemical molecular device that combines the determination of the light-driven electron transfer processes with the elucidation of the mechanistic details of the photo-induced hydrogen evolution reaction.

The discovery of new materials for electrochemical CO2 reduction can take inspiration from biology and geology. Indeed, in the context of the hydrothermal vent theory of the Emergence of Life, alkaline vents represent a system of significant interest. These vents involve an alkaline, H2 and HS− rich fluid that meets the carbonic acidulous primordial ocean, resulting in the precipitation of a mineral barrier composed of iron sulfides and oxyhydroxides. This inorganic membrane separates the two fluids, generating an electrochemical potential difference. This ΔE can be dissipated by coupling CO2 reduction (on the acidic side) with H2 or HS-oxidation (on the alkaline side), potentially leading to the generation of the very first organic molecules on Earth. In this study, mackinawite [FeSm] and violarite [Fe,Ni)3S4] were synthesized through homogeneous precipitation, their structures and electrochemical properties were characterized. Electrodes based on these materials were prepared and tested for CO2 reduction. It was found that FeSm can reduce CO2 to formic acid and methanol, while (Fe,Ni)3S4 preferentially generates formic acid and carbon monoxide at − 0.82 V vs RHE. The results also indicate that very low overpotential is required for HCOOH generation on mackinawite. The proof that CO2 reduction under these conditions occurs electrochemically, rather than purely chemically, is evidenced by the absence of CO2 reduction products without the application of an electrical bias. Although the efficiency of these materials is currently limited, the potential for CO2 reduction using earth-abundant elements such as iron, nickel, and sulfur is promising. Further engineering of these materials could lead to cost-effective technology.

Chlorinated trityl radicals functionalized with electron-donating groups are promising red-emitting materials for optoelectronic and spintronic applications, overcoming the spin-statistical limit of conventional emitters. Donor functionalization induces charge transfer character, enhancing photoluminescence quantum yield, which depends on the donor strength and its orientation. However, donor functionalized tris(trichlorophenyl)methyl radicals show lower quantum yield than their perchlorinated derivatives, likely due to weaker donor-acceptor electronic coupling and enhanced non-radiative decay. We present a novel trityl derivative with two additional chlorines that restrict the orientation of the donor to a nearly perpendicular arrangement towards the trityl plane, minimizing vibronic coupling and non-radiative losses. Spectroscopic and computational studies reveal that this steric con-straint improves the photoluminescence quantum yield compared to the tris(trichlorophenyl)methyl analogues. These findings highlight the potential of donor-acceptor decoupling to enable efficient, red-shifted emission, offering a design strategy for high-performance radical emitters.

The optimized geometry of Intermediates from Photocatalytic Hydrogen Evolution Reaction of RuPtI2 Photocatalyst are obtained from Density Functional Theory (DFT) calculation. Here, the B3LYP/def2svp level of theory within MeCN (SMD Implicit Solvent Model) are implemented for geometry optimization. For correcting the electronic energy, M06/def2TZVP is used in this mechanistic study. All of calculation are done by Gaussian 16 Software. The name of Intermediates are following the original paper and its Supplementary Information.

Conversion of CO2 to hard carbon is an interesting technology for the removal of carbon dioxide from the atmosphere. Recently, it was shown that CeO2 can selectively catalyse this reaction but we still lack information regarding the reaction mechanism. Using density functional theory (DFT) modelling we explore possible reaction mechanisms that allow for the polymerization of CO2. According to our computations the reaction is initialized by the adsorption of CO2 in an oxygen vacancy. Owing to the rich defect chemistry of ceria a large number of suitable sites are available at the surface. C-C bond formation is achieved through an aldol condensation type mechanism which comprises the electrochemical elimination of water to form a carbene. This carbene then performs a nucleophilic attack on CO2 . The reaction mechanism possesses significant similarities to the corresponding reaction in synthetic organic chemistry. Since the mechanism is completely generic it allows for all relevant steps of the formation of hard carbon like chain growth, chain linkage and the formation of side chains or aromatic rings. Surprisingly, ceria mainly serves as an anchor for CO2 in an oxygen vacancy while all other subsequent reaction steps are almost completely independent from the catalyst. These insights are important for the development of novel catalysts for CO2 reduction and may also lead to new reactions for the electrosynthesis of organic molecules.

P2-type layered oxides are attractive cathode active materials for sodium-ion batteries, however, these materials typically suffer from detrimental Na+/vacancy orderings. In this work, we investigate the origin as well as the influence of the transition metal ratio on Na+/vacancy orderings in P2-type cathode materials. A combination of X-ray diffraction (XRD), neutron diffraction, advanced electrochemical methods, operando XRD and DFT calculations is applied to study Na+/vacancy orderings in P2-NaxNi1/3Mn2/3O2 and P2-NaxMn3/4Ni1/4O2. In P2-NaxNi1/3Mn2/3O2, a honeycomb Ni/Mn superstructure leads to charge ordering within the transition metal slab and pronounced Na+/vacancy orderings, causing distinct voltage jumps at specific sodium contents (x = 2/3, 1/2 and 1/3). For P2-Na0.60Mn3/4Ni1/4O2, the Ni/Mn superstructure is disrupted, resulting in more complex charge orderings within the transition metal slab, partially suppressed Na+/vacancy orderings and an overall smoother potential profile. Based on our findings, guidelines to suppress Na+/vacancy orderings in P2-type cathode materials for sodium-ion batteries are postulated and discussed with respect to electrochemical measurements of various transition metal compositions. These guidelines can serve to predict the tendency towards Na+/vacancy orderings for a given cathode composition or to design new cathode compositions for enhanced cycle life based on the absence of Na+/vacancy orderings.

Formox, a highly energy-intensive process, currently serves as the primary source of formaldehyde (HCHO), for which there is a crucial and steadily growing chemical demand. The alternative electrochemical production of HCHO from C1 carbon sources such as CO2 and CO is still in its early stages, with even the few identified cases lacking mechanistic rationalization. In this study, we demonstrate that cobalt phthalocyanine (CoPc) immobilized on multiwalled carbon nanotubes (MW-CNTs) constitutes an excellent electrocatalytic system for producing HCHO with productivity through the direct reduction of CO, the two-electron reduction product of CO2. By carefully adjusting both the pH and the applied potential, we identified conditions that enable the production of HCHO with a partial current density of 0.64 mA cm-2 (17.5% Faradaic efficiency, FE) and a total FE of 61.2% for the liquid products (formaldehyde and methanol). A reduction mechanism is proposed.

Carbon dioxide reduction reaction (CO2 RR) is a promising method for converting CO2 into value-added products. CO2 RR over single atom catalysts (SAC) is widely known to result in chemical compounds such as carbon monoxide and formic acid that contain only one carbon atom (C1). Indeed, at least two active sites are commonly believed to be required for C-C coupling to synthesize compounds such as ethanol and propylene (C2+ ) from CO2 . However, experimental evidence suggests that Iron Phthalocyanine (PcFe), which possesses only a single metal center, can produce a trace amount of C2+ products. To the best of our knowledge, the mechanism by which C2+ products are formed over a SAC such as PcFe is still unknown. Using density functional theory (DFT), we analyzed the mechanism of CO2 RR to C1 and C2+ products over PcFe. Due to the high concentration of bicarbonate at pH=7, CO2 RR competes with HCO3 – reduction. Our computations indicate, that bicarbonate reduction is significantly more favourable. However, the rate of this reaction is influenced by H3 O+ concentration. For the formation of C2+ products, our computations reveals that C-C coupling proceeds through the reaction between in-situ formed CO and PcFe("0")-CH2 or PcFe("-I")-CH2 intermediates. This reaction step is highly exergonic and requires only low activation energies of 0.44 eV and 0.24 eV for PcFe("0")-CH2 and PcFe("-I")-CH2 . The DFT results, in line with experimental evidence, suggest that C2+ compounds are produced over PcFe at low potentials whereas CH4 is still the main post-CO product.

•The most accurate guess of the absolute potential in water is 4.31(±0.07) eV.•The most accurate guess of the proton solvation energy in water is −11.38(±0.07) eV.•Predictions in non-aqueous solvents are unreliable owing to shortcomings of the implicit solvation models.

Proton-electron transfer (PET) reactions are rather common in chemistry and crucial in energy storage applications. How electrons and protons are involved or which mechanism dominates is strongly molecule and pH dependent. It is the nature of the participants in the reaction that dictates how electrons and protons are involved and which mechanism dominates. Quantum chemical methods can be used to assess redox potential and acidity constant values but the computations are rather time consuming. In this work, supervised machine learning (ML) models are used to predict PET reactions and analyze molecular space. The data for ML have been created by density functional theory (DFT) calculations. Random Forest Regression models are trained and tested on a dataset that we created. The dataset contains more than 8200 organic molecules that each underwent a two-proton two-electron transfer process. Both structural and chemical descriptors are used. The HOMO of the reactant and LUMO of the product participating in the oxidation reaction appeared to be inversely associated with \oxE. Trained models using a SMILES-based descriptor can efficiently predict the pKa and redox potential with a mean absolute error of less than 1 and 66 mV, respectively. High prediction accuracy of $R^2 > 0.76$ and $> 0.90$ was also obtained on the external test set for redox potential and pKa, respectively. This hybrid DFT-ML study can be applied to speed up the screening of quinone-type molecules for energy storage and other applications.

Carbon dioxide reduction is a promising approach to convert CO2 to value-added products. Carbon dioxide electroreduction is commonly performed at neutral pH where CO2, H2CO3, HCO3-, and CO3-2 are in equilibrium. Despite this, only CO2 is commonly considered as the active species while H2CO3, HCO3-, and CO3-2 (carbonate species) are neglected. Using density functional theory (DFT), we investigate the contribution of carbonate species in the CO2 electroreduction reaction over a Fe-porphyrin (Fe(ppy)) model system. We find that the hydrogen evolution reaction (HER) is blocked by a high activation barrier of 1.54 eV associated with the Fe("I") (ppy)-H formation. This is opposed to the reduction of H2CO3 and HCO3- whose rate-limiting step requires significantly lower activation energies of approximately 0.4 eV. Direct CO2 reduction on the other hand requires to overcome a rate-limiting barrier of 0.95 eV for the CO2 adsorption step. Based on these results we suggest that H2CO3 and HCO3- are the true reactants for the electrochemical "CO2"RR over Fe(ppy).

Abstract Finding an alternative to Cr(VI) as catalyst for the conversion of hypochlorite/hypochlorous acid to chlorate is of critical importance to render the industrial chlorate process safe and sustainable. Recently, telluric acid was identified as a potential replacement but its performance under industrial conditions and its interactions with other parts of the process are still unknown. These factors are elucidated by a combination of density functional theory (DFT) modeling and pilot plant studies. Our results indicate, that the addition of telluric acid indeed has a beneficial effect on the decomposition of HOCl to chlorate. The increased performance, shown as a decreased oxygen formation and an increase in anodic current efficiency. It is mostly related to a buffering effect and an increased selectivity for chlorate formation. Unfortunately, a low cathodic current efficiency was achieved due to reduction of telluric acid to solid Te/TeO2 particles in the electrolyte and at the cathode. Despite the benefits of buffering effects and increased selectivity for chlorate formation, telluric acid is unsuitable as replacement for Cr(VI) in the chlorate process due to lack of compatibility with all process conditions.

CO 2 reduction is typically performed at neutral pH. Under these conditions CO 2 is in equilibrium with H 2 CO 3 , HCO 3 − and CO 3 2− . However, despite their presence so far most studies solely focus on the contribution of CO 2 while carbonate species as alternative reactants are generally neglected. Using density functional theory (DFT) modelling we explore the possible contribution of these carbonate species to the overall CO 2 reduction activity for a Fe porphyrin model catalyst. Considering only reaction Gibbs free energies, we find the reduction of carbonic acid (H 2 CO 3 ), bicarbonate (HCO 3 − ) and CO 2 to be equally likely. However, owing to a very high activation barrier for the initial adsorption of CO 2 onto the catalyst, bicarbonate and carbonic acid reduction are found to be several orders of magnitude faster. These data are used to model the pH dependence of the reaction rates of the different reactants. These results confirm that carbonic acid and bicarbonate are the most likely reactants independent of the pH and reactor setup.

Understanding the structure and chemical bonding in water dimers is central to the study of many (photo-)electrochemical oxidation reactions. Two structures of the water dimer radical cation, namely, proton-transfer and hemi-bonded structures, have been suggested using density functional theory (DFT) and coupled cluster singles, doubles, and perturbative triples [CCSD(T)]. Both structures are identified by us as local minima, and their relative stability strongly depends on the level of theory. The exact exchange correlates linearly to the energy difference between both local minima. DFT functionals with less than 20 percent exact exchange predict the hemi-bonded structure to be more stable, while more than 20 percent of the exact exchange stabilizes the proton-transfer structure. The latter structure is also confirmed by CCSD(T) benchmark computations. These computations, furthermore, indicate that the oxidized water dimer consists of a hydronium cation (H3O+) and an HO· radical. These results are reproduced by DFT functionals with more than 50% of exact exchange (BHandH, M06-2X, and M06-HF). The transition barrier for the interconversion from the proton-transfer to the hemi-bonded structure is 0.6 eV, while the reverse reaction has a barrier of 0.1 eV.

Chlorate is produced through electrolysis of a chloride containing electrolyte in an undivided cell. Cr(VI) is added to the electrolyte in order to minimize the amount of oxygen formed through the homogeneous decomposition of hypochlorite. Despite the importance of Cr(VI) for the chlorate process we posses only very limited knowledge regarding the active Cr(VI) species and mechanisms through which it aids chlorate formation and inhibits O 2 evolution. Using density functional theory (DFT) modeling we present for the first time a detailed reaction mechanism for the chromate catalyzed chlorate formation. Our calculations indicate, that the reaction is initialized by the formation of a Cr(VI)‐O−ClOCl species which forms Cr(VI)‐OClO intermediate. This step is found to be rate determining with a rate constant which is comparable to the disproportionation reaction without catalyst. Chlorate is then obtained either through an uncatalyzed oxidation of chlorite to chlorate or the nucleophilic attack of OCl − followed by a second Cl − elimination step. The comparison of the activity of the different Cr(VI) species reveals that only CrO 4 2− is active whereas HCrO 4 − and Cr 2 O 7 2− display sluggish kinetics.

The mixture of CO and H2, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO2 and H2O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO2 and H2O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20–50 °C. The experimental results show that for all the applied potentials the ratio of H2/CO increases with increasing temperature. Interestingly, at −0.6 VRHE and 40 °C, the H2/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at −1.0 VRHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pKa value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.