Acid anion electrolyte effects on platinum for oxygen and hydrogen electrocatalysis

Rational Dual-Atom Design to Boost Oxygen Reduction Reaction on Iron-Based Electrocatalysts

The oxygen reduction reaction (ORR) is critical for energy conversion technologies like fuel cells and metal-air batteries. However, advancing efficient and stable ORR catalysts remains a significant challenge. Iron-based single-atom catalysts (Fe SACs) have emerged as promising alternatives to precious metals. However, their catalytic performance and stability remain constrained. Introducing a second metal (M) to construct Fe─M dual-atom catalysts (Fe─M DACs) is an effective strategy to enhance the performance of Fe SACs. This review provides a comprehensive overview of the recent advancements in Fe-based DACs for ORR. It begins by examining the structural advantages of Fe─M DACs from the perspectives of electronic structure and reaction pathways. Next, the precise synthetic strategies for DACs are discussed, and the structure-performance relationships are explored, highlighting the role of the second metal in improving catalytic activity and stability. The review also covers in situ characterization techniques for real-time observation of catalytic dynamics and reaction intermediates. Finally, future directions for Fe─M DACs are proposed, emphasizing the integration of advanced experimental strategies with theoretical simulations as well as artificial intelligence/machine learning to design highly active and stable ORR catalysts, aiming to expand the application of Fe─M DACs in energy conversion and storage technologies.

Role of Water in Green Carbon Science

Within the context of green chemistry, the concept of green carbon science emphasizes carbon balance and recycling to address the challenge of achieving carbon neutrality. The fundamental processes in this field are oxidation and reduction, which often involve simple molecules such as CO2, CO, CH4, CHx, and H2O. Water plays a critical role in nearly all oxidation-reduction processes, and thus, it is a central focus of research in green carbon science. Water can act as a direct source of dihydrogen in reduction reactions or participate in oxidation reactions, frequently involving O-O coupling to produce hydrogen peroxide or dioxygen. At the atomic level, this coupling involves the statistically unfavorable proximity of two atoms, requiring optimization through a catalytic process influenced by two types of factors, as described by the authors. Extrinsic factors are related to geometrical and electronic criteria associated with the catalytic metal, involving its d-orbitals (or bands in the case of zerovalent metals and electrodes). Intrinsic factors are related to the coupling of oxygen atoms via their p-orbitals. At the mesoscopic or microscopic scale, the reaction medium typically consists of mixtures of lipophilic and hydrophilic phases with water, which may exist under supercritical conditions or as suspensions of microdroplets. These reactions predominantly occur at phase interfaces. A comprehensive understanding of the phenomena across these scales could facilitate improvements and even lead to the development of novel conversion processes.

Halogen Thermochemistry Assessed with Density Functional Theory: Systematic Errors, Swift Corrections and Effects on Electrochemistry

Despite its sizable errors, density functional theory (DFT) is extensively used to evaluate thermochemical properties of gases, liquids and their interfaces with solids. As numerous halogen-containing compounds appear as reactants, products and/or electrolytes in electrochemical reactions, and ionic effects are currently an active area of research, it is important to evaluate the accuracy of DFT for halogen thermochemistry. Herein, we assess the formation energies of interhalogens, hydrogen halides, diatomic and atomic halogens and their ions using six widespread functionals at the GGA, meta-GGA and hybrid levels. We observe that DFT errors with respect to experiments are correlated with the electronegativity of the species and there are systematic trends across functionals, such that swift corrections were devised. Specifically, the average of the mean absolute errors for the six functionals decreased from 0.19 eV before the corrections to 0.08 eV after them. Besides, the overall maximum absolute error (MAX) decreased from 0.76 to 0.44 eV and the average of the MAXs decreased from 0.51 to 0.24 eV. Finally, we illustrate the qualitative and quantitative impact of gas-phase errors on the predictions of surface Pourbaix diagrams.

Unraveling Oxyanion Effects on Oxygen Evolution Electrocatalysis of Nickel Hydr(oxy)oxides: The Critical Role of Fe Impurities

Electrolyte modulation can enhance the performance of electrocatalysts for the oxygen evolution reaction (OER) by tailoring the electrocatalyst-electrolyte interface, but the role of anion additives remains controversial. Herein, we report our findings on unraveling the effects of oxyanions (NO3-, SO42-, and PO43-) and identifying Fe impurities as the key factor driving OER activity enhancement in Ni hydr(oxy)oxide model catalysts. Fe impurities, introduced via oxyanion salts, significantly enhance OER activity, while oxyanions themselves have minimal direct impact when Fe ions are removed. Our results, including operando Raman spectroscopy, reveal that Fe enhances Ni reducibility/redox reversibility. X-ray absorption spectroscopy and density functional theory calculations indicate that Fe preferentially adsorbs on Ni surface sites with higher deprotonation energy. These findings reveal the critical role of surface-adsorbed Fe in modulating Ni hydr(oxy)oxide activity and highlight overlooked impurity effects in electrocatalysis when studying additive effects in electrolyte modulation.

Employing a Zn-air/Photo-Electrochemical Cell for In Situ Generation of H2O2 for Onsite Control of Pollutants

Industrial production of hydrogen peroxide (H2O2) is energy-intensive and generates unwanted byproducts. Herein, an alternative production strategies of H2O2 are demonstrated in a Zn-air and a photoelectrochemical cell. Employing an optimally produced reduced graphene oxide (rGO) electrocatalyst@air-cathode, an impressive power density of 320 Wmgeo -2 (geo = geometric area) is achieved along with a high H2O2 production rate of 3.17 mol mgeo -2h-1 (operating potential = 0.8 V). Systematic investigations reveal the critical role of specific functional groups (viz. C─O─C, chemisorbed O2, C≐C) to be responsible for enhancing the yield of H2O2. The in situ generated superoxide (O2˙) and hydroxyl radicals (˙OH) act as oxidants to efficiently degrade onsite, a model textile dye pollutant (viz. rhodamine B) inside the Zn-air cell. Using the identical rGO as the photoelectrode in an H-type cell, the H2O2 production is remarkably enhanced under visible light illumination. Simultaneously, the onsite pollutant degradation occurs five times faster than the Zn-air cell (at the same operating potential = 0.8 V). This work opens a new paradigm for electrosynthesis, wherein an underlying redox can be utilized to synthesize industrial chemicals for onsite control of environmental pollution sustainably.

Oxidation of interfacial cobalt controls the pH dependence of the oxygen evolution reaction

Transition metal oxides often undergo dynamic surface reconstruction under oxygen evolution reaction conditions to form the active state, which differs in response to the electrolyte pH. The resulting pH dependency of catalytic activity is commonly observed but poorly understood. Herein we track Co oxidation state changes at different pH-directed (hydr)oxide/electrolyte interfaces using operando X-ray absorption spectroscopy characterizations. Combined with in situ electrochemical analyses, we establish correlations between Co redox dynamics, the flat band potential and Co oxidation state changes to explain the pH dependency of the oxygen evolution activity. Alkaline environments provide a low flat band potential that yields a low-potential Co redox transformation, which favours surface reconstruction. Neutral and acidic environments afford an anodic shift of the Co redox transformation that increases the catalytic overpotential. The larger overpotential in neutral environments is attributable to poor Co atom polarizability and slow Co oxidation state changes. These findings reveal that interfacial Co oxidation state changes directly determine the pH dependency of the oxygen evolution reaction activity.

Crystal-size-dependent Optical Properties of H-atoms on the Nodes of Ti-based Metal-organic Framework

Proton-coupled electron transfer (PCET) reactions are fundamental to energy storage and conversion processes. By coupling electrons with protons, the net charge neutrality is retained, preventing electrode decomposition due to charge imbalance. PCET reactions with equimolar amounts of protons and electrons can be considered as a net H-atom transfer (HAT) reaction. Many redox-active metal-organic frameworks (MOFs) have demonstrated that the inorganic nodes and/or the organic linkers can be tailored to undergo HAT reactions. In particular, the Ti-oxo nodes of the MOF focused on this work, Ti-MIL-125, can accept up to two H-atoms. H-atom binding on the nodes of Ti-MIL-125 has long been known to correlate with the color change in the crystals from white to blue-black, but its exact optical properties, such as molar extinction coefficient (ϵ) and wavelength with maximum ϵ, λmax, have yet to be determined. The presented work determines these parameters using colloidally stable Ti-MIL-125 of three different crystallite sizes. These studies revealed that both parameters are highly dependent on the crystal size and are likely indicating a distortion of the Ti-oxo nodes at the crystal surface. Together, these highlight the importance of considering defects in understanding HAT reactions of otherwise structurally uniform and periodic MOFs.

Self-Reconstruction of High Entropy Alloys for Efficient Alkaline Hydrogen Evolution

Alkaline water (H2O) electrolysis is currently a commercialized green hydrogen (H2) production technology, yet the unsatisfactory hydrogen evolution reaction (HER) performance severely limits its energy conversion efficiency and cost reduction. Herein, PtRu2.9Fe0.15Co1.5Ni1.3 high entropy alloys (HEAs) is synthesized and subsequently exploited electrochemically induced structural oxidation processes to construct self-reconfigurable HEAs, as an efficient alkaline HER catalyst. The optimized self-reconstructed PtRu2.9Fe0.15Co1.5Ni1.3 HEAs with the HEAs and cobalt rutheniate interface (HEAs-Co2RuO4) exhibits excellent alkaline HER performance, requiring just 11.8 mV to obtain a current density (j) of 10 mA cm-2 in 1 m KOH. And the j on HEAs-Co2RuO4 is 41.8 mA cm-2 at 0.07 VRHE, 2.0 and 6.1 times higher than PtRu2.9Fe0.15Co1.5Ni1.3 HEAs and 20% Pt/C. Mechanism studies reveal that the improved alkaline HER performance of HEAs-Co2RuO4 is due to the formation of HEAs-Co2RuO4, which significantly shrinks the Helmholtz layer, provides a new fast material transport channel, boosts H2O adsorption, and reduces hydrogen adsorption, and thus accelerates the alkaline HER. This research not only throws new light on the self-reconstruction of catalysts but also provides guidance for the rational design of efficient electrocatalysts.

Small extracellular vesicles derived from sequential stimulation of canine adipose-derived mesenchymal stem cells enhance anti-inflammatory activity

BACKGROUND

Small extracellular vesicles (sEVs) derived from mesenchymal stem cells (MSCs) are recognized for their therapeutic potential in immune modulation and tissue repair, especially in veterinary medicine. This study introduces an innovative sequential stimulation (IVES) technique, involving low-oxygen gas mixture preconditioning using in vitro fertilization gas (IVFG) and direct current electrical stimulation (ES20), to enhance the anti-inflammatory properties of sEVs from canine adipose-derived MSCs (cAD-MSCs). Initial steps involved isolation and comprehensive characterization of cAD-MSCs, including morphology, gene expression, and differentiation potentials, alongside validation of the electrical stimulation protocol. IVFG, ES20, and IVES were applied simultaneously with a control condition. Stimulated cAD-MSCs were evaluated for morphological changes, cell viability, and gene expressions. Conditioned media were collected and purified for sEV isolation on Day1, Day2, and Day3. To validate the efficacy of IVES for sEV production, various analyses were conducted, including microscopic examination, surface marker assessment, zeta-potential measurement, protein quantification, nanoparticle tracking analysis, and determination of anti-inflammatory activity.

RESULTS

We found that IVES demonstrated non-cytotoxicity and induced crucial genotypic changes associated with sEV production in cAD-MSCs. Interestingly, IVFG influenced cellular adaptation, while ES20 induced hypoxia activation. By merging these stimulations, IVES enhanced sEV stability and quality profiles. The cAD-MSC-derived sEVs exhibited anti-inflammatory activity in lipopolysaccharide-induced RAW264.7 macrophages, emphasizing their improved effectiveness without cytotoxicity or immunogenicity. These effects were consistent across day 3 collection, indicating the establishment of an effective protocol for sEV production.

CONCLUSIONS

This research established an innovative sequential stimulation method with positive impact on sEV characteristics including stability, quality, and anti-inflammatory activity. This study not only contributes to the enhancement of sEV production but also sheds light on their functional aspects for therapeutic interventions.

Hydrogen Peroxide Electrosynthesis via Selective Oxygen Reduction Reactions Through Interfacial Reaction Microenvironment Engineering

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a compelling alternative for decentralized and on-site H2O2 production compared to the conventional anthraquinone process. To advance this electrosynthesis system, there is growing interest in optimizing the interfacial reaction microenvironment to boost electrocatalytic performance. This review consolidates recent advancements in reaction microenvironment engineering for the selective electrocatalytic conversion of O2 to H2O2. Starting with fundamental insights into interfacial electrocatalytic mechanisms, an overview of various strategies for constructing the favorable local reaction environment, including adjusting electrode wettability, enhancing mesoscale mass transfer, elevating local pH, incorporating electrolyte additives, and employing pulsed electrocatalysis techniques is provided. Alongside these regulation strategies, the corresponding analyses and technical remarks are also presented. Finally, a summary and outlook on critical challenges, suggesting future research directions to inspire microenvironment engineering and accelerate the practical application of H2O2 electrosynthesis is delivered.

Metal-Independent Correlations for Site-Specific Binding Energies of Relevant Catalytic Intermediates

Establishing energy correlations among different metals can accelerate the discovery of efficient and cost-effective catalysts for complex reactions. Using a recently introduced coordination-based model, we can predict site-specific metal binding energies (ΔE M) that can be used as a descriptor for chemical reactions. In this study, we have examined a range of metals including Ag, Au, Co, Cu, Ir, Ni, Os, Pd, Pt, Rh, and Ru and found linear correlations between predicted ΔE M and adsorption energies of CH and O (ΔE CH and ΔE O) at various coordination environments for all the considered metals. Interestingly, all the metals correlate with one another under specific surface site coordination, indicating that different metals are interrelated in a particular coordination environment. Furthermore, we have tested and verified for PtPd- and PtIr-based alloys that they follow a similar behavior. Moreover, we have expanded the metal space by taking some early transition metals along with a few s-block metals and shown a cyclic behavior of the adsorbate binding energy (ΔE A) versus ΔE M. Therefore, ΔE CH and ΔE O can be efficiently interpolated between metals, alloys, and intermetallics based on information related to one metal only. This simplifies the process of screening new metal catalyst formulations and their reaction energies.

Integrated electrocatalytic synthesis of ammonium nitrate from dilute NO gas on metal organic frameworks-modified gas diffusion electrodes

The electrocatalytic conversion of NO offers a promising technology for not only removing the air pollutant but also synthesizing valuable chemicals. We design an integrated-electrocatalysis cell featuring metal organic framework (MOF)-modified gas diffusion electrodes for simultaneous capture of NO and generation of NH4NO3 under low-concentration NO flow conditions. Using 2% NO gas, the modified cathode exhibits a higher NH4+ yield and Faradaic efficiency than an unmodified cathode. Notably, the modified cathode shows a twofold increase in NH4+ production with 20 ppm NO gas supply. Theoretical calculations predict favorable transfer of adsorbed NO from the adsorption layer to the catalyst layer, which is experimentally confirmed by enhanced NO mass transfer from gas to electrolyte across the modified electrode. The adsorption layer-modified anode also exhibits a higher NO3- yield for NO electro-oxidation compared to the unmodified electrode under low NO concentration flow. Among various integrated-cell configurations, a single-chamber setup produces a higher NH4NO3 yield than a double-chamber setup. Furthermore, a higher NO utilization efficiency is obtained with a single-gasline operation mode, where the NO-containing gas flows sequentially from the cathode to the anode.

Advancing H2O2 electrosynthesis: enhancing electrochemical systems, unveiling emerging applications, and seizing opportunities

Hydrogen peroxide (H2O2) is a highly desired chemical with a wide range of applications. Recent advancements in H2O2 synthesis center on the electrochemical reduction of oxygen, an environmentally friendly approach that facilitates on-site production. To successfully implement practical-scale, highly efficient electrosynthesis of H2O2, it is critical to meticulously explore both the design of catalytic materials and the engineering of other components of the electrochemical system, as they hold equal importance in this process. Development of promising electrocatalysts with outstanding selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while well-configured electrolyzers determine the practical implementation of large-scale H2O2 production. In this review, we systematically summarize fundamental mechanisms and recent achievements in H2O2 electrosynthesis, including electrocatalyst design, electrode optimization, electrolyte engineering, reactor exploration, potential applications, and integrated systems, with an emphasis on active site identification and microenvironment regulation. This review also proposes new insights into the existing challenges and opportunities within this rapidly evolving field, together with perspectives on future development of H2O2 electrosynthesis and its industrial-scale applications.

Ultrasmall and Highly Dispersed Pt Entities Deposited on Mesoporous N-doped Carbon Nanospheres by Pulsed CVD for Improved HER

Vapor-based deposition techniques are emerging approaches for the design of carbon-supported metal powder electrocatalysts with tailored catalyst entities, sizes, and dispersions. Herein, a pulsed CVD (Pt-pCVD) approach is employed to deposit different Pt entities on mesoporous N-doped carbon (MPNC) nanospheres to design high-performance hydrogen evolution reaction (HER) electrocatalysts. The influence of consecutive precursor pulse number (50-250) and deposition temperature (225-300 °C) are investigated. The Pt-pCVD process results in highly dispersed ultrasmall Pt clusters (≈1 nm in size) and Pt single atoms, while under certain conditions few larger Pt nanoparticles are formed. The best MPNC-Pt-pCVD electrocatalyst prepared in this work (250 pulses, 250 °C) reveals a Pt HER mass activity of 22.2 ± 1.2 A mg-1 Pt at -50 mV versus the reversible hydrogen electrode (RHE), thereby outperforming a commercially available Pt/C electrocatalyst by 40% as a result of the increased Pt utilization. Remarkably, after optimization of the Pt electrode loading, an ultrahigh Pt mass activity of 56 ± 2 A mg-1 Pt at -50 mV versus RHE is found, which is among the highest Pt mass activities of Pt single atom and cluster-based electrocatalysts reported so far.

Facet-Dependent Oxygen Evolution Reaction Activity of IrO2 from Quantum Mechanics and Experiments

The diversity of chemical environments present on unique crystallographic facets can drive dramatic differences in catalytic activity and the reaction mechanism. By coupling experimental investigations of five different IrO2 facets and theory, we characterize the detailed elemental steps of the surface redox processes and the rate-limiting processes for the oxygen evolution reaction (OER). The predicted complex evolution of surface adsorbates and the associated charge transfer as a function of applied potential matches well with the distinct redox features observed experimentally for the five facets. Our microkinetic model from grand canonical quantum mechanics (GC-QM) calculations demonstrates mechanistic differences between nucleophilic attack and O-O coupling across facets, providing the rates as a function of applied potential. These GC-QM calculations explain the higher OER activity observed on the (100), (001), and (110) facets and the lower activity observed for the (101) and (111) facets. This combined study with theory and experiment brings new insights into the structural features that either promote or hinder the OER activity of IrO2, which are expected to provide parallels in structural effects on other oxide surfaces.

Condensed Layer Deposition of Nanoscopic TiO2 Overlayers on High-Surface-Area Electrocatalysts

Encapsulating an electrocatalytic material with a semipermeable, nanoscopic oxide overlayer offers a promising approach to enhancing its stability, activity, and/or selectivity compared to an unencapsulated electrocatalyst. However, applying nanoscopic oxide encapsulation layers to high-surface-area electrodes such as nanoparticle-supported porous electrodes is a challenging task. This study demonstrates that the recently developed condensed layer deposition (CLD) method can be used for depositing nanoscopic (sub-10 nm thick) titanium dioxide (TiO2) overlayers onto high-surface-area platinized carbon foam electrodes. Characterization of the overlayers by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) showed that the films are amorphous, while X-ray photoelectron spectroscopy confirmed that they exhibit TiO2 stoichiometry. Electrodes were also characterized by hydrogen underpotential deposition (Hupd) and carbon monoxide (CO) stripping, demonstrating that the Pt electrocatalysts remain electrochemically active after encapsulation. Additionally, copper underpotential deposition (Cuupd) measurements revealed that TiO2 overlayers are effective at blocking Cu2+ from reaching the TiO2/Pt buried interface and were used to estimate that between 43 and 98% of Pt surface sites were encapsulated. Overall, this study shows that CLD is a promising approach for depositing nanoscopic protective overlayers on high-surface-area electrodes.

Selective Electrified Propylene-to-Propylene Glycol Oxidation on Activated Rh-Doped Pd

Renewable-energy-powered electrosynthesis has the potential to contribute to decarbonizing the production of propylene glycol, a chemical that is used currently in the manufacture of polyesters and antifreeze and has a high carbon intensity. Unfortunately, to date, the electrooxidation of propylene under ambient conditions has suffered from a wide product distribution, leading to a low faradic efficiency toward the desired propylene glycol. We undertook mechanistic investigations and found that the reconstruction of Pd to PdO occurs, followed by hydroxide formation under anodic bias. The formation of this metastable hydroxide layer arrests the progressive dissolution of Pd in a locally acidic environment, increases the activity, and steers the reaction pathway toward propylene glycol. Rh-doped Pd further improves propylene glycol selectivity. Density functional theory (DFT) suggests that the Rh dopant lowers the energy associated with the production of the final intermediate in propylene glycol formation and renders the desorption step spontaneous, a concept consistent with experimental studies. We report a 75% faradic efficiency toward propylene glycol maintained over 100 h of operation.

Recent advances in the role of interfacial liquids in electrochemical reactions

The interfacial liquid, situated in proximity to an electrode or catalyst, plays a vital role in determining the activity and selectivity of crucial electrochemical reactions, including hydrogen evolution, oxygen evolution/reduction, and carbon dioxide reduction. Thus, there has been a growing interest in better understanding the behavior and the catalytic effect of its constituents. This minireview examines the impact of interfacial liquids on electrocatalysis, specifically the effects of water molecules and ionic species present at the interface. How the structure of interfacial water, distinct from the bulk, can affect charge transfer kinetics and transport of species is presented. Furthermore, how cations and anions (de)stabilize intermediates and transition states, compete for adsorption with reaction species, and act as local environment modifiers including pH and the surrounding solvent structure are described in detail. These effects can promote or inhibit reactions in various ways. This comprehensive exploration provides valuable insights for tailoring interfacial liquids to optimize electrochemical reactions.

Solutal Marangoni effect determines bubble dynamics during electrocatalytic hydrogen evolution

Understanding and manipulating gas bubble evolution during electrochemical water splitting is a crucial strategy for optimizing the electrode/electrolyte/gas bubble interface. Here gas bubble dynamics are investigated during the hydrogen evolution reaction on a well-defined platinum microelectrode by varying the electrolyte composition. We find that the microbubble coalescence efficiency follows the Hofmeister series of anions in the electrolyte. This dependency yields very different types of H2 gas bubble evolution in different electrolytes, ranging from periodic detachment of a single H2 gas bubble in sulfuric acid to aperiodic detachment of small H2 gas bubbles in perchloric acid. Our results indicate that the solutal Marangoni convection, induced by the anion concentration gradient developing during the reaction, plays a critical role at practical current density conditions. The resulting Marangoni force on the H2 gas bubble and the bubble departure diameter therefore depend on how surface tension varies with concentration for different electrolytes. This insight provides new avenues for controlling bubble dynamics during electrochemical gas bubble formation.

Electric Double Layer Effects in Electrocatalysis: Insights from Ab Initio Simulation and Hierarchical Continuum Modeling

Structures of the electric double layer (EDL) at electrocatalytic interfaces, which are modulated by the material properties, the electrolyte characteristics (e.g., the pH, the types and concentrations of ions), and the electrode potential, play crucial roles in the reaction kinetics. Understanding the EDL effects in electrocatalysis has attracted substantial research interest in recent years. However, the intrinsic relationships between the specific EDL structures and electrocatalytic kinetics remain poorly understood, especially on the atomic scale. In this Perspective, we briefly review the recent advances in deciphering the EDL effects mainly in hydrogen and oxygen electrocatalysis through a multiscale approach, spanning from the atomistic scale simulated by ab initio methods to the macroscale by a hierarchical approach. We highlight the importance of resolving the local reaction environment, especially the local hydrogen bond network, in understanding EDL effects. Finally, some of the remaining challenges are outlined, and an outlook for future developments in these exciting frontiers is provided.

Electrochemical Wastewater Refining: A Vision for Circular Chemical Manufacturing

Wastewater is an underleveraged resource; it contains pollutants that can be transformed into valuable high-purity products. Innovations in chemistry and chemical engineering will play critical roles in valorizing wastewater to remediate environmental pollution, provide equitable access to chemical resources and services, and secure critical materials from diminishing feedstock availability. This perspective envisions electrochemical wastewater refining─the use of electrochemical processes to tune and recover specific products from wastewaters─as the necessary framework to accelerate wastewater-based electrochemistry to widespread practice. We define and prescribe a use-informed approach that simultaneously serves specific wastewater-pollutant-product triads and uncovers a mechanistic understanding generalizable to broad use cases. We use this approach to evaluate research needs in specific case studies of electrocatalysis, stoichiometric electrochemical conversions, and electrochemical separations. Finally, we provide rationale and guidance for intentionally expanding the electrochemical wastewater refining product portfolio. Wastewater refining will require a coordinated effort from multiple expertise areas to meet the urgent need of extracting maximal value from complex, variable, diverse, and abundant wastewater resources.

Role of mutations in a chemoenzymatic enantiodivergent C(sp3)-H insertion: exploring the mechanism and origin of stereoselectivity

New-to-nature enzymes have emerged as powerful catalysts in recent years for streamlining various stereoselective organic transformations. While synthetic strategies employing engineered enzymes have witnessed proliferating success, there is limited clarity on the mechanistic front and more so when considering molecular-level insights into the role of selected mutations, dramatically escalating catalytic competency and selectivity. We have investigated the mechanism and correlation between mutations and exquisite stereoselectivity of a lactone carbene insertion into the C(sp3)-H bond of substituted aniline, catalyzed by two mutants of a cytochrome P450 variant, "P411" (engineered through directed evolution) in which the axial cysteine has been mutated to serine, utilizing various computational tools. The pivotal role of S264 and L/R328 mutations in the active site has been delineated computationally using two cluster models, thus rationalizing the enantiodivergence. This report provides much-needed insights into the origin of enantiodivergence, furnishing a mechanistic framework for understanding the anchoring effects of H-bond donor residues with the lactone ring. This study is expected to have important implications in the rational design of stereodivergent enzymes and toward successful in silico enzyme designing.

Hydrogen-Bond Regulation of the Microenvironment of Ni(II)-Porphyrin Bifunctional Electrocatalysts for Efficient Overall Water Splitting

Accurately regulating the microenvironment around active sites is an important approach for boosting the overall water splitting performance of bifunctional electrocatalysts, which can drive both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in the same electrolyte. Herein, pseudo-pyridine-substituted Ni(II)-porphyrins (o-NiTPyP, m-NiTPyP, and p-NiTPyP) with pseudo-pyridine N-atoms located at the ortho-, meta-, or para-position are prepared and used as model catalysts for alkaline water splitting. Experimental and theoretical results reveal that the pseudo-pyridine N-atom positions can regulate the microenvironment around the active sites and the adsorption free energy of H-donating substances by affecting the H-bonding interaction and the NNiN bond angles of active sites, and thus those pseudo-pyridine-substituted Ni(II)-porphyrins deliver better electrocatalytic activity than the Ni(II)-tetraphenylporphyrin (NiTPP) without pseudo-pyridine N-atoms. Among them, m-NiTPyP on carbon nanotubes delivers the lowest overpotentials of 267 and 138 mV at 10 mA cm^-2 for the OER and HER, respectively. Specifically, m-NiTPyP as bifunctional electrocatalyst in an alkaline electrolyzer requires only 1.62 V to drive efficient overall water splitting at 10 mA cm^-2 while remaining durable. This work proposes a new H-bond-regulating approach of the microenvironment of electrocatalysts for effectively boosting the overall water splitting activity and deeply understanding its related mechanism.

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms, Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg^-1 _Pt and 11.7 ± 0.6 A mg^-1 _Cat at -50 mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.

Effect of Surface-Adsorbed and Intercalated (Oxy)anions on the Oxygen Evolution Reaction

As the kinetically demanding oxygen evolution reaction (OER) is crucial for the decarbonization of our society, a wide range of (pre)catalysts with various non-active-site elements (e.g., Mo, S, Se, N, P, C, Si…) have been investigated. Thermodynamics dictate that these elements oxidize during industrial operation. The formed oxyanions are water soluble and thus predominantly leach in a reconstruction process. Nevertheless, recently, it was unveiled that these thermodynamically stable (oxy)anions can adsorb on the surface or intercalate in the interlayer space of the active catalyst. There, they tune the electronic properties of the active sites and can interact with the reaction intermediates, changing the OER kinetics and potentially breaking the persisting OER *OH/*OOH scaling relations. Thus, the addition of (oxy)anions to the electrolyte opens a new design dimension for OER catalysis and the herein discussed observations deepen the understanding of the role of anions in the OER.