Liquid Metal-Enabled Tunable Synthesis of Nanoporous Polycrystalline Copper for Selective CO2-to-Formate Electrochemical Conversion.

Copper-based catalysts exhibit high activity in electrochemical CO2 conversion to value-added chemicals. However, achieving precise control over catalysts design to generate narrowly distributed products remains challenging. Herein, a gallium (Ga) liquid metal-based approach is employed to synthesize hierarchical nanoporous copper (HNP Cu) catalysts with tailored ligament/pore and crystallite sizes. The nanoporosity and polycrystallinity are generated by dealloying intermetallic CuGa2 formed after immersing pristine Cu foil in liquid Ga in a basic or acidic solution. The liquid metal-based approach allows for the transformation of monocrystalline Cu to the polycrystalline HNP Cu with enhanced CO2 reduction reaction (CO2RR) performance. The dealloyed HNP Cu catalyst with suitable crystallite size (22.8 nm) and nanoporous structure (ligament/pore size of 45 nm) exhibits a high Faradaic efficiency of 91% toward formate production under an applied potential as low as -0.3 VRHE. The superior CO2RR performance can be ascribed to the enlarged electrochemical catalytic surface area, the generation of preferred Cu facets, and the rich grain boundaries by polycrystallinity. This work demonstrates the potential of liquid metal-based synthesis for improving catalysts performance based on structural design, without increasing compositional complexity.

Ru-Induced Defect Engineering in Co3O4 Lattice for High Performance Electrochemical Reduction of Nitrate to Ammonium.

Amidst these growing sustainability concerns, producing NH4 + via electrochemical NO3 - reduction reaction (NO3RR) emerges as a promising alternative to the conventional Haber-Bosch process. In a pioneering approach, this study introduces Ru incorporation into Co3O4 lattices at the nanoscale and further couples it with electroreduction conditioning (ERC) treatment as a strategy to enhance metal oxide reducibility and induce oxygen vacancies, advancing NH4 + production from NO3RR. Here, supported by a suite of ex situ and in situ characterization measurements, the findings reveal that Ru enrichment promotes Co species reduction and oxygen vacancy formation. Further, as evidenced by the theoretical calculations, Ru integration lowers the energy barrier for oxygen vacancy formation, thereby facilitating a more energy-efficient NO3RR-to-NH4 + pathway. Optimal catalytic activity is realized with a Ru loading of 10 at.% (named 10Ru/Co3O4), achieving a high NH4 + production rate (98 nmol s-1 cm-2), selectivity (97.5%) and current density (≈100 mA cm-2) at -1.0 V vs RHE. The findings not only provide insights into defect engineering via the incorporation of secondary sites but also lay the groundwork for innovative catalyst design aimed at improving NH4 + yield from NO3RR. This research contributes to the ongoing efforts to develop sustainable electrochemical processes for nitrogen cycle management.

From Plastic Waste to Green Hydrogen and Valuable Chemicals Using Sunlight and Water.

Over 79 % of 6.3 billion tonnes of plastics produced from 1950 to 2015 have been disposed in landfills or found their way to the oceans, where they will reside for up to hundreds of years before being decomposed bringing upon significant dangers to our health and ecosystems. Plastic photoreforming offers an appealing alternative by using solar energy and water to transform plastic waste into value-added chemical commodities, while simultaneously producing green hydrogen via the hydrogen evolution reaction. This review aims to provide an overview of the underlying principles of emerging plastic photoreforming technologies, highlight the challenges associated with experimental protocols and performance assessments, discuss recent global breakthroughs on the photoreforming of plastics, and propose perspectives for future research. A critical assessment of current plastic photoreforming studies shows a lack of standardised conditions, hindering comparison amongst photocatalyst performance. Guidelines to establish a more accurate evaluation of materials and systems are proposed, with the aim to facilitate the translation of promising fundamental discovery in photocatalysts design.

Electrosynthesis of Hydrogen Peroxide through Selective Oxygen Reduction: A Carbon Innovation from Active Site Engineering to Device Design.

Electrochemical synthesis of hydrogen peroxide (H2 O2 ) through the selective oxygen reduction reaction (ORR) offers a promising alternative to the energy-intensive anthraquinone method, while its success relies largely on the development of efficient electrocatalyst. Currently, carbon-based materials (CMs) are the most widely studied electrocatalysts for electrosynthesis of H2 O2 via ORR due to their low cost, earth abundance, and tunable catalytic properties. To achieve a high 2e- ORR selectivity, great progress is made in promoting the performance of carbon-based electrocatalysts and unveiling their underlying catalytic mechanisms. Here, a comprehensive review in the field is presented by summarizing the recent advances in CMs for H2 O2 production, focusing on the design, fabrication, and mechanism investigations over the catalytic active moieties, where an enhancement effect of defect engineering or heteroatom doping on H2 O2 selectivity is discussed thoroughly. Particularly, the influence of functional groups on CMs for a 2e- -pathway is highlighted. Further, for commercial perspectives, the significance of reactor design for decentralized H2 O2 production is emphasized, bridging the gap between intrinsic catalytic properties and apparent productivity in electrochemical devices. Finally, major challenges and opportunities for the practical electrosynthesis of H2 O2 and future research directions are proposed.

Understanding the Role of (W, Mo, Sb) Dopants in the Catalyst Evolution and Activity Enhancement of Co3 O4 during Water Electrolysis via In Situ Spectroelectrochemical Techniques.

Unlocking the potential of the hydrogen economy is dependent on achieving green hydrogen (H2 ) production at competitive costs. Engineering highly active and durable catalysts for both oxygen and hydrogen evolution reactions (OER and HER) from earth-abundant elements is key to decreasing costs of electrolysis, a carbon-free route for H2 production. Here, a scalable strategy to prepare doped cobalt oxide (Co3 O4 ) electrocatalysts with ultralow loading, disclosing the role of tungsten (W), molybdenum (Mo), and antimony (Sb) dopants in enhancing OER/HER activity in alkaline conditions, is reported. In situ Raman and X-ray absorption spectroscopies, and electrochemical measurements demonstrate that the dopants do not alter the reaction mechanisms but increase the bulk conductivity and density of redox active sites. As a result, the W-doped Co3 O4 electrode requires ≈390 and ≈560 mV overpotentials to reach ±10 and ±100 mA cm-2 for OER and HER, respectively, over long-term electrolysis. Furthermore, optimal Mo-doping leads to the highest OER and HER activities of 8524 and 634 A g-1 at overpotentials of 0.67 and 0.45 V, respectively. These novel insights provide directions for the effective engineering of Co3 O4 as a low-cost material for green hydrogen electrocatalysis at large scales.

Advancing MXene Electrocatalysts for Energy Conversion Reactions: Surface, Stoichiometry, and Stability.

MXenes, due to their tailorable chemistry and favourable physical properties, have great promise in electrocatalytic energy conversion reactions. To exploit fully their enormous potential, further advances specific to electrocatalysis revolving around their performance, stability, compositional discovery and synthesis are required. The most recent advances in these aspects are discussed in detail: surface functional and stoichiometric modifications which can improve performance, Pourbaix stability related to their electrocatalytic operating conditions, density functional theory and advances in machine learning for their discovery, and prospects in large scale synthesis and solution processing techniques to produce membrane electrode assemblies and integrated electrodes. This Review provides a perspective that is complemented by new density functional theory calculations which show how these recent advances in MXene material design are paving the way for effective electrocatalysts required for the transition to integrated renewable energy systems.

Engineering Multidefects on Cex Si1- x O2- δ Nanocomposites for the Catalytic Ozonation Reaction.

Herein, it is shown that by engineering defects on Cex Si1- x O2- δ nanocomposites synthesized via flame spray pyrolysis, oxygen vacancies can be created with an increased density of trapped electrons, enhancing the formation of reactive oxygen species (ROSs) and hydroxyl radicals in an ozone-filled environment. Spectroscopic analysis and density functional theory calculations indicate that two-electron oxygen vacancies (OV 0 ) or peroxide species, and their degree of clustering, play a critical role in forming reactive radicals. It is also found that a higher Si content in the binary oxide imposes a high OV 0 ratio and, consequently, higher catalytic activity. Si inclusion in the nanocomposite appears to stabilize the surface oxygen vacancies as well as increase the reactive electron density at these sites. A mechanistic study on effective ROSs generated during catalytic ozonation reveals that the hydroxyl radical is the most effective ROS for organic degradation and is formed primarily through H2 O2 generation in the presence of the OV 0 . Examining the binary oxides offers insights on the contribution of oxygen vacancies and their state of charge to catalytic reactions, in this instance for the catalytic ozonation of organic compounds.

Two-Dimensional Ultra-Thin Nanosheets with Extraordinarily High Drug Loading and Long Blood Circulation for Cancer Therapy.

Nanoparticle drug delivery is largely restricted by the low drug loading capacity of nanoparticle carriers. To address this critical challenge and maximize the potential of nanoparticle drug delivery, a 2D ultra-thin layered double hydroxide (LDH) nanosheet with exceptionally high drug loading, excellent colloidal stability, and prolonged blood circulation for cancer treatment is constructed. The nanosheet is synthesized via a biocompatible polymer-assisted bottom-up method and exhibits an ultra-thin 2D sheet-like structure that enables a considerable amount of cargo anchoring sites available for drug loading, leading to an extraordinary 734% (doxorubicin/nanoparticle mass ratio) drug loading capacity. Doxorubicin delivered by the nanosheet remains stable on the nanosheet carrier under the physiological pH condition, while showing sustained release in the tumor microenvironment and the intracellular environment, thus demonstrating on-demand drug release as a result of pH-responsive biodegradation of nanosheets. Using in vitro and in vivo 4T1 breast cancer models, the nanosheet-based ultra-high drug-loading system demonstrates even enhanced therapeutic performance compared to the multilayered LDH-based high drug-loading system, in terms of increased cellular uptake efficiency, prolonged blood circulation, superior therapeutic effect, and reduced systemic toxicity.

Highly Selective Metal-Free Electrochemical Production of Hydrogen Peroxide on Functionalized Vertical Graphene Edges.

Electrochemical generation of hydrogen peroxide (H2 O2 ) is an attractive alternative to the energy-intensive anthraquinone oxidation process. Metal-free carbon-based materials such as graphene show great promise as efficient electrocatalysts in alkaline media. In particular, the graphene edges possess superior electrochemical properties than the basal plane. However, identification and enhancement of the catalytically active sites at the edges remain challenging. Furthermore, control of surface wettability to enhance gas diffusion and promote the performance in bulk electrolysis is largely unexplored. Here, a metal-free edge-rich vertical graphene catalyst is synthesized and exhibits a superior performance for H2 O2 production, with a high onset potential (0.8 V versus reversible hydrogen electrode (RHE) at 0.1 mA cm-2 ) and 100% Faradaic efficiency at various potentials. By tailoring the oxygen-containing functional groups using various techniques of electrochemical oxidation, thermal annealing and oxygen plasma post-treatment, the edge-bound in-plane ether-type (COC) groups are revealed to account for the superior catalytic performance. To manipulate the surface wettability, a simple vacuum-based method is developed to effectively induce material hydrophobicity by accelerating hydrocarbon adsorption. The increased hydrophobicity greatly enhances gas transfer without compromising the Faradaic efficiency, enabling a H2 O2 productivity of 1767 mmol gcatalyst -1 h-1 at 0.4 V versus RHE.

Improved carrier dynamics in nickel/urea-functionalized carbon nitride for ethanol photoreforming.

Photoreforming has been shown to accelerate the H2 evolution rate compared to water splitting due to thermodynamically favorable organic oxidation. In addition, the potential to simultaneously produce solar fuel and value-added chemicals is a significant benefit of photoreforming. To achieve an efficient and economically viable photoreforming process, the selection and design of an appropriate photocatalyst is essential. Carbon nitride is promising as a metal-free photocatalyst with visible light activity, high stability, and low fabrication cost. However, it typically exhibits poor photogenerated charge carrier dynamics, thereby resulting in low photocatalytic performance. Herein, we demonstrate improved carrier dynamics in urea-functionalized carbon nitride with in situ photodeposited Ni cocatalyst (Ni/Urea-CN) for ethanol photoreforming. In the presence of 1 mM Ni2+ precursor, an H2 evolution rate of 760.5 µmol h-1 g-1 and an acetaldehyde production rate of 888.2 µmol h-1 g-1 were obtained for Ni/Urea-CN. The enhanced activity is ascribed to the significantly improved carrier dynamics in Urea-CN. The ability of oxygen moieties in the urea group to attract electrons and to increase the hole mobility via a positive shift in the valence band promotes an improvement in the overall carrier dynamics. In addition, high crystallinity and specific surface area of the Urea-CN contributed to accelerating charge separation and transfer. As a result, the electrons were efficiently transferred from Urea-CN to the Ni cocatalyst for H2 evolution while the holes were consumed during ethanol oxidation. The work demonstrates a means by which carrier dynamics can be tuned by engineering carbon nitride via edge functionalization.

Constructing Interfacial Boron-Nitrogen Moieties in Turbostratic Carbon for Electrochemical Hydrogen Peroxide Production.

The electrochemical oxygen reduction reaction (ORR) provides a green route for decentralized H2 O2 synthesis, where a structure-selectivity relationship is pivotal for the control of a highly selective and active two-electron pathway. Here, we report the fabrication of a boron and nitrogen co-doped turbostratic carbon catalyst with tunable B-N-C configurations (CNB-ZIL) by the assistance of a zwitterionic liquid (ZIL) for electrochemical hydrogen peroxide production. Combined spectroscopic analysis reveals a fine tailored B-N moiety in CNB-ZIL, where interfacial B-N species in a homogeneous distribution tend to segregate into hexagonal boron nitride domains at higher pyrolysis temperatures. Based on the experimental observations, a correlation between the interfacial B-N moieties and HO2 - selectivity is established. The CNB-ZIL electrocatalysts with optimal interfacial B-N moieties exhibit a high HO2 - selectivity with small overpotentials in alkaline media, giving a HO2 - yield of ≈1787 mmol gcatalyst -1 h-1 at -1.4 V in a flow-cell reactor.

Manipulating the Fate of Charge Carriers with Tungsten Concentration: Enhancing Photoelectrochemical Water Oxidation of Bi2 WO6.

Bismuth tungstate (Bi2 WO6 ) thin film photoanode has exhibited an excellent photoelectrochemical (PEC) performance when the tungsten (W) concentration is increased during the fabrication. Plate-like Bi2 WO6 thin film with distinct particle sizes and surface area of different exposed facets are successfully prepared via hydrothermal reaction. The smaller particle size in conjunction with higher exposure extent of electron-dominated {010} crystal facet leads to a shorter electron transport pathway to the bulk surface, assuring a lower charge transfer resistance and thus minimal energy loss. In addition, it is proposed based on the results from conductive atomic force microscopy that higher W concentration plays a crucial role in facilitating the charge transport of the thin film. The "self-doped" of W in Bi2 WO6 will lead to the higher carrier density and improved conductivity. Thus, the variation in the W concentration during a synthesis can be served as a promising strategy for future W based photoanode design to achieve high photoactivity in water splitting application.

Accelerating Electron-Transfer and Tuning Product Selectivity Through Surficial Vacancy Engineering on CZTS/CdS for Photoelectrochemical CO2 Reduction.

Copper-based chalcogenides have been considered as potential photocathode materials for photoelectrochemical (PEC) CO2 reduction due to their excellent photovoltaic performance and favorable conduction band alignment with the CO2 reduction potential. However, they suffer from low PEC efficiency due to the sluggish charge transfer kinetics and poor selectivity, resulting from random CO2 reduction reaction pathways. Herein, a facile heat treatment (HT) of a Cu2 ZnSnS4 (CZTS)/CdS photocathode is demonstrated to enable significant improvement in the photocurrent density (-0.75 mA cm-2 at -0.6 V vs RHE), tripling that of pristine CZTS, as a result of the enhanced charge transfer and promoted band alignment originating from the elemental inter-diffusion at the CZTS/CdS interface. In addition, rationally regulated CO2 reduction selectivity toward CO or alcohols can be obtained by tailoring the surficial sulfur vacancies by HT in different atmospheres (air and nitrogen). Sulfur vacancies replenished by O-doping is shown to favor CO adsorption and the CC coupling pathway, and thereby produce methanol and ethanol, whilst the CdS surface with more S vacancies promotes CO desorption capability with higher selectivity toward CO. The strategy in this work rationalizes the interface charge transfer optimization and surface vacancy engineering simultaneously, providing a new insight into PEC CO2 reduction photocathode design.

Industrial carbon dioxide capture and utilization: state of the art and future challenges.

Dramatically increased CO2 concentration from several point sources is perceived to cause severe greenhouse effect towards the serious ongoing global warming with associated climate destabilization, inducing undesirable natural calamities, melting of glaciers, and extreme weather patterns. CO2 capture and utilization (CCU) has received tremendous attention due to its significant role in intensifying global warming. Considering the lack of a timely review on the state-of-the-art progress of promising CCU techniques, developing an appropriate and prompt summary of such advanced techniques with a comprehensive understanding is necessary. Thus, it is imperative to provide a timely review, given the fast growth of sophisticated CO2 capture and utilization materials and their implementation. In this work, we critically summarized and comprehensively reviewed the characteristics and performance of both liquid and solid CO2 adsorbents with possible schemes for the improvement of their CO2 capture ability and advances in CO2 utilization. Their industrial applications in pre- and post-combustion CO2 capture as well as utilization were systematically discussed and compared. With our great effort, this review would be of significant importance for academic researchers for obtaining an overall understanding of the current developments and future trends of CCU. This work is bound to benefit researchers in fields relating to CCU and facilitate the progress of significant breakthroughs in both fundamental research and commercial applications to deliver perspective views for future scientific and industrial advances in CCU.

Bi-Sn Catalytic Foam Governed by Nanometallurgy of Liquid Metals.

Metallic foams, with intrinsic catalytic properties, are critical for heterogeneous catalysis reactions and reactor designs. Market ready catalytic foams are costly and made of multimaterial coatings with large sub-millimeter open cells providing insufficient active surface area. Here we use the principle of nanometallurgy within liquid metals to prepare nanostructured catalytic metal foams using a low-cost alloy of bismuth and tin with sub-micrometer open cells. The eutectic bismuth and tin liquid metal alloy was processed into nanoparticles and blown into a tin and bismuth nanophase separated heterostructure in aqueous media at room temperature and using an indium brazing agent. The CO2 electroconversion efficiency of the catalytic foam is presented with an impressive 82% conversion efficiency toward formates at high current density of -25 mA cm-2 (-1.2 V vs RHE). Nanometallurgical process applied to liquid metals will lead to exciting possibilities for expanding industrial and research accessibility of catalytic foams.

Intrinsic ORR Activity Enhancement of Pt Atomic Sites by Engineering the d-Band Center via Local Coordination Tuning.

A considerable amount of platinum (Pt) is required to ensure an adequate rate for the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. Thus, the implementation of atomic Pt catalysts holds promise for minimizing the Pt content. In this contribution, atomic Pt sites with nitrogen (N) and phosphorus (P) co-coordination on a carbon matrix (PtNPC) are conceptually predicted and experimentally developed to alter the d-band center of Pt, thereby promoting the intrinsic ORR activity. PtNPC with a record-low Pt content (≈0.026 wt %) consequently shows a benchmark-comparable activity for ORR with an onset of 1.0 VRHE and half-wave potential of 0.85 VRHE . It also features a high stability in 15 000-cycle tests and a superior turnover frequency of 6.80 s-1 at 0.9 VRHE . Damjanovic kinetics analysis reveals a tuned ORR kinetics of PtNPC from a mixed 2/4-electron to a predominately 4-electron route. It is discovered that coordinated P species significantly shifts d-band center of Pt atoms, accounting for the exceptional performance of PtNPC.

Surface strategies for catalytic CO2 reduction: from two-dimensional materials to nanoclusters to single atoms.

Redox catalysis, including photocatalysis and (photo)electrocatalysis, may alleviate global warming and energy crises by removing excess CO2 from the atmosphere and converting it to value-added resources. Nano-to-atomic two-dimensional (2D) materials, clusters and single atoms are superior catalysts because of their engineerable ultrathin/small dimensions and large surface areas and have attracted worldwide research interest. Given the current gap between research and applications in CO2 reduction, our review systematically and constructively discusses nano-to-atomic surface strategies for catalysts reported to date. This work is expected to drive and benefit future research to rationally design surface strategies with multi-parameter synergistic impacts on the selectivity, activity and stability of next-generation CO2 reduction catalysts, thus opening new avenues for sustainable solutions to climate change, energy and environmental issues, and the potential industrial economy.

N,P Co-Coordinated Manganese Atoms in Mesoporous Carbon for Electrochemical Oxygen Reduction.

The increasing interest in fuel cell technology encourages the development of efficient and low-cost electrocatalysts to replace the Pt based materials for catalyzing the cathodic oxygen reduction reaction (ORR). In the present work, a nitrogen and phosphorus co-coordinated manganese atom embedded mesoporous carbon composite (MnNPC-900) is successfully prepared via a polymerization of o-phenylenediamine followed by calcination at 900 °C. The MnNPC-900 composite shows a high ORR activity in alkaline media, offering an onset potential of 0.97 V, and a half-wave potential of 0.84 V (both vs reversible hydrogen electrode) with a loading of 0.4 mg cm-2 . This performance not only exceeds its phosphorus-free counterpart (MnNC-900), but also is comparable to the Pt/C catalyst under identical measuring conditions. The significantly enhanced ORR performance of MnNPC-900 can be ascribed to: i) the introduction of phosphorus assists the generation of mesopores during the pyrolysis and endows the MnNPC-900 composite with large surface area and pore volume, thus facilitating the mass transfer process and increases the number of exposed active sites. ii) The formation of N,P co-coordinated atomic-scale Mn sites (MnNx Py ), which modifies the electronic configuration of the Mn atoms and thereby boosts the ORR catalytic activity.

Ferrous ion as a reducing agent in the generation of antibiofilm nitric oxide from a copper-based catalytic system.

The work found that the electron-donating properties of ferrous ions (Fe2+) can be used for the conversion of nitrite (NO2-) into the biofilm-dispersing signal nitric oxide (NO) by a copper(II) complex (CuDTTCT) catalyst, a potentially applicable biofilm control technology for the water industries. The availability of Fe2+ varied depending on the characteristics of the aqueous systems (phosphate- and carbonate-containing nitrifying bacteria growth medium, NBGM and phosphate buffered saline, PBS at pH 6 to 8, to simulate conditions typically present in the water industries) and was found to affect the production of NO from nitrite by CuDTTCT (casted into PVC). Greater amounts of NO were generated from the CuDTTCT-nitrite-Fe2+ systems in PBS compared to those in NBGM, which was associated with the reduced extent of Fe2+-to-Fe3+ autoxidation by the iron-precipitating moieties phosphates and carbonate in the former system. Further, acidic conditions at pH 6.0 were found to favor NO production from the catalytic system in both PBS and NBGM compared to neutral or basic pH (pH 7.0 or 8.0). Lower pH was shown to stabilize Fe2+ and reduce its autoxidation to Fe3+. These findings will be beneficial for the potential implementation of the NO-generating catalytic technology and indeed, a 'non-killing' biofilm dispersal activity of CuDTTCT-nitrite-Fe2+ was observed on nitrifying bacteria biofilms in PBS at pH 6.

Photocorrosion of Cuprous Oxide in Hydrogen Production: Rationalising Self-Oxidation or Self-Reduction.

Cuprous Oxide (Cu2 O) is a photocatalyst with severe photocorrosion issues. Theoretically, it can undergo both self-oxidation (to form copper oxide (CuO)) and self-reduction (to form metallic copper (Cu)) upon illumination with the aid of photoexcited charges. There is, however, limited experimental understanding of the "dominant" photocorrosion pathway. Both photocorrosion modes can be regulated by tailoring the conditions of the photocatalytic reactions. Photooxidation of Cu2 O (in the form of a suspension system), accompanied by corroded morphology, is kinetically favourable and is the prevailing deactivation pathway. With knowledge of the dominant deactivation mode of Cu2 O, suppression of self-photooxidation together with enhancement in its overall photocatalytic performance can be achieved after a careful selection of sacrificial hole (h+ ) scavenger. In this way, stable hydrogen (H2 ) production can be attained without the need for deposition of secondary components.