Electrocatalytic upcycling of polyethylene terephthalate to commodity chemicals and H2 fuel

Modulating Adsorption Behavior by Single-site Pt on RuO2 for Efficient Electrosynthesis of Glycolic Acid from Plastic Wastes

Electrochemical upcycling of polyethylene terephthalate (PET) wastes into valuable glycolic acid (GA) is an ideal solution for resource utilization. However, simultaneously achieving high activity and selectivity remains challenging due to the over-oxidation and C-C cleavage during ethylene glycol (EG) oxidation in PET hydrolysate. Herein, we develop an atomically isolated Pt on RuO2 (Pt1/RuO2) catalyst composed of high-density Pt-Ru interfaces that ensure single-site adsorption of EG, enrich surface *OH coverage and weaken *CO-CH2OH intermediate adsorption, thereby synergistically promoting GA generation. Specifically, Pt1/RuO2 delivers a remarkable mass activity of 8.09 A/mgPt, as well as a high GA Faradaic efficiency (95.3 %) and selectivity (96.9 %). Under membrane electrode assembly conditions, Pt1/RuO2 realizes a stable electrolysis over 500 h at 6 A with a GA yield rate of 4.06 g h-1. In-depth theoretical and in situ spectroscopic investigations reveal the synergy between isolated Pt and oxophilic RuO2 plays a crucial role in high-efficiency EG-to-GA conversion. This study offers valuable insights for the rational design of advanced catalysts for GA synthesis from PET wastes via a single-site doped bimetallic strategy.

Product Oriented Upcycling of Waste Polyethylene Terephthalate Plastic and Carbon Dioxide via Decoupled Electrolysis

End-of-life plastics and carbon dioxide (CO2) are anthropogenic waste carbon resources; it is imperative to develop efficient technologies to convert them to value-added products. Here we report the upcycling of polyethylene terephthalate (PET) plastic and CO2 toward valuable potassium diformate, terephthalic acid, and H2 fuel via decoupled electrolysis. This product-oriented process is realized by two electrolyzers: (1) a solid-state-electrolyte based CO2 electrolyzer and (2) a solid-polymer-electrolyte-based PET electrolyzer. Using a bismuth-based catalyst, the CO2 electrolyzer showed more than 140 h continuous operation at current of 250 mA, resulting in 850 mL pure HCOOH solution with a concentration of 683 mM. Furthermore, we constructed a solid-polymer-electrolyte electrolyzer with an electrode area of 50 cm2 for the electrooxidation of ethylene glycol to formate, achieving 30 A of current at ~1.9 V cell voltage and 80 % formate Faradaic efficiency. With this electrolyzer, we demonstrated the efficient transformation of PET hydrolysate to a mixture of terephthalate and formate. Additionally, combining CO2 derived HCOOH and PET electrolyte, we obtained recycled terephthalic acid and potassium diformate. This work provides an integrated strategy for the valorization of waste carbon resources with less using external resources.

Electrocatalytic reforming of polyethylene terephthalate waste plastics into high-value-added chemicals with green hydrogen generation

Electrochemical reforming offers a sustainable strategy for converting plastic waste into high-value-added chemicals and hydrogen fuel. Herein, a cost-effective NiFe-filmed electrode with a Tremella-like nanostructure was developed using an ultrasonic immersion etching method. This electrode enabled the electro-reforming of ethylene glycol (EG, a monomer of polyethylene terephthalate (PET)) into valuable commodity chemicals, with coproduction of hydrogen fuel. This system demonstrated notable electrocatalytic performance, achieving a current density of 100 mA/cm2 at a low overpotential of 1.52 V vs. reversible hydrogen electrode (RHE). It also exhibits notable selectivity (94.4 %) and Faradaic efficiency (94.3 %) for formate production. Furthermore, in a proof-of-concept demonstration, real-world PET plastic waste was successfully utilized to produce potassium diformate and terephthalic acid with properties comparable to those of commercial products. This study provides a comprehensive strategy for designing cost-effective catalysts for plastic electro-upcycling and lays a foundation for advancing the circular economy of plastic waste.

Deciphering the Role of Second Metal in M-Ni (M = Fe, Ni, and Mn) Heterobimetallic Electrocatalysts in Controlling the HAT versus Hydride Transfer Mechanism for the Dehydrogenation of Alcohols

The second 3d-transition metal incorporation in Ni-(oxy)hydroxide has a drastic effect on alkaline OER and alcohol dehydrogenation reactivity. While Mn incorporation suppresses the alkaline OER, it greatly improves the alcohol dehydrogenation reactivity. A complete reversal of reactivity is obtained when Fe is incorporated, which shows better performance for alkaline OER with poor alcohol dehydrogenation reactivity. The role of the second 3d-metal is elusive due to the lack of systematic mechanistic studies. In this report, we thoroughly analyzed a series of M─Ni (M = Fe, Ni, Mn) (oxy)hydroxides derived from electrochemical activation of M-MOF grown on nickel foam for its electrochemical activity in alkaline OER and aliphatic, benzyl alcohol dehydrogenation. With the help of pH-dependence and kinetic isotope effect studies, the potential-determining step (PDS) and the rate-determining step (RDS) have been elucidated. The Hammett analysis revealed critical information about the transition state and offered insight into the hydrogen atom transfer (HAT) versus hydride transfer (HT) for alcohol dehydrogenation operative in various heterobimetallic electrocatalysts. Further, the superior alcohol dehydrogenation reactivity of NiMn catalyst for PET hydrolysate electro-oxidation is extended to afford valuable chemicals with concomitant production of hydrogen.

Manipulating Interfacial Water Via Metallic Pt1Co6 Sites on Self-Adaptive Metal Phosphides to Enhance Water Electrolysis

Metallizing active sites to control the structural and kinetic dissociation of water at the catalyst-electrolyte interface, along with elucidating its mechanism under operating conditions, is a pivotal innovation for the hydrogen evolution reaction (HER). Here, a design of singly dispersed Pt-Co sites in a fully metallic state on nanoporous Co2P, tailored for HER, is introduced. An anion-exchange-membrane water electrolyzer equipped with this catalyst can achieve the industrial current densities of 1.0 and 2.0 A cm-2 at 1.71 and 1.85 V, respectively. It is revealed that the singly dispersed Pt-Co sites undergo self-adaptive distortion under operating conditions, which form a Pt1Co6 configuration with a strongly negative charge that optimizes reactant binding and reorganizes the interfacial water structure, resulting in an improved concentration of potassium (K+) ions in the closest ion plane. The K+ ions interact cooperatively with H2O (K·H2O), which strengthens the Pt-H binding interaction and facilitates the polarization of the H─OH bond, leading to improved HER activity. This study not only propels the advancement of cathodic catalysts for water electrolysis but also delineates a metallization strategy and an interface design principle, thereby enhancing electrocatalytic reaction rates.

Protective effect of curcumin against microplastic and nanoplastics toxicity

Microplastics and nanoplastics (MNPs) are present in urban dust and the aquatic environments of industrialized cities. MNPs in the human body accumulate in the lymphoid follicles, Peyer's patches of the gastrointestinal tract, and pulmonary vascular endothelial cells, which slowly result in toxicity. Since previous studies introduced curcumin as a natural protective agent against environmental toxins, we reviewed preclinical studies that had used curcumin to protect organs or cells from toxicity secondary to exposure to MNPs. It was found that exposure to MNPs resulted in osteolysis, immunotoxicity, thyroid disturbances, nephrotoxicity, neurotoxicity, hepatotoxicity, pulmonary toxicity, gastrointestinal toxicity, cardiovascular toxicity, and especially endocrine, and reproductive toxicity. Nevertheless, except for one study reviewed, curcumin restored all oxidative and histopathological damages induced by MNPs to normal due to curcumin's inherent antioxidant, antiapoptotic, anti-inflammatory, and anti-proliferative properties.

Polyoxometalated metal-organic framework superstructure for stable water oxidation

Stable, nonprecious catalysts are vital for large-scale alkaline water electrolysis. Here, we report a grafted superstructure, MOF@POM, formed by self-assembling a metal-organic framework (MOF) with polyoxometalate (POM). In situ electrochemical transformation converts MOF into active metal (oxy)hydroxides to produce a catalyst with a low overpotential of 178 millivolts at 10 milliamperes per square centimeter in alkaline electrolyte. An anion exchange membrane water electrolyzer incorporating this catalyst achieves 3 amperes per square centimeter at 1.78 volts at 80°C and stable operation at 2 amperes per square centimeter for 5140 hours at room temperature. In situ electrochemical spectroscopy and theoretical studies reveal that the synergistic interactions between metal atoms create a fast electron-transfer channel from catalytic iron and cobalt sites, nickel, and tungsten in the polyoxometalate to the electrode, stabilizing the metal sites and preventing dissolution.

Photocatalytic Conversion of Polyester-Derived Alcohol into Value-Added Chemicals by Engineering Atomically Dispersed Pd Catalyst

Photoreforming presents a promising strategy for upcycling waste polyester-derived alcohol into valuable chemicals. However, it remains a great challenge due to its low performance and unsatisfactory selectivity toward high-value C2 products. Here, we report the highly efficient and selective conversion of ethylene glycol (EG, a monomer of polyethylene terephthalate (PET)) to glycolaldehyde using atomically dispersed Pd species supported on TiO2 catalyst. A glycolaldehyde production rate of 5072 μmol gcat -1 h-1 with a selectivity of 90.0 % and long-term durability can be achieved. Experimental and theoretical results show that Pd single atoms can enhance the photocatalytic activity by enriching the photogenerated holes, which are the dominant species for the selective oxidation of EG to glycolaldehyde. More importantly, the adsorption of EG molecules on the catalysts is significantly promoted, which is subsequently transformed into RO⋅ radicals, a crucial intermediate in producing glycolaldehyde. Additionally, Pd single atoms on TiO2 enable the reduction of the glycolaldehyde desorption barrier, thereby facilitating high selectivity and inhibiting further oxidation to C1 products. This work provides new insights into the photocatalytic conversion of polyester wastes by atomic engineering.

Electrocatalytic Ethylene Glycol to Long-Chain C3+ α-Hydroxycarboxylic Acids via Cross-Coupling with Primary Alcohols

Electrocatalytic conversion of ethylene glycol (EG) into α-hydroxycarboxylic acids (α-HCAs) holds great importance for advancing sustainable chemical development since EG is widely accessible in polyethylene terephthalate (PET) plastic and biomass. Herein, we report the direct electrocatalytic cross-coupling of EG and primary C1-C4 alcohol, producing carbon-chain-propagated C3-C6 α-HCAs over a gold (Au) catalyst. Taking EG and methanol (MeOH) cross-coupling to lactic acid (LA) as an example, experimental evidence shows that stabilization of the aldehyde intermediates (glycolaldehyde and formaldehyde from EG and MeOH, respectively) without overoxidation is important for the following cross-coupling via aldol condensation and thus LA formation. Based on this understanding, we systematically modulate the catalyst and reaction conditions, achieving a high LA productivity of 268.1 μmol cm-2 h-1 with a Faradaic efficiency of 28.7% at a constant current of 100 mA cm-2. The carbon-chain propagation strategy shows generality for EG cross-coupling with C1-C4 primary alcohols, successfully producing C3-C6 α-HCAs. As a proof of concept, a postconsumer PET bottle is converted to LA with a good productivity of 224.5 μmol cm-2 in a 2 h electrolysis. This work demonstrates the possibility of the electrocatalytic strategy to convert EG into long-chain compounds via C-C bond cross-coupling, representing a crucial step toward building a sustainable society.

State-of-the-art and perspectives of hydrogen generation from waste plastics

Waste plastic utilization and hydrogen production present significant economic and social challenges but also offer opportunities for research and innovation. This review provides a comprehensive analysis of the latest advancements and innovations in hydrogen generation coupled with waste plastic recycling. It explores various strategies, including pyrolysis, gasification, aqueous phase reforming, photoreforming, and electrocatalysis. Pyrolysis and gasification in combination with catalytic reforming or water gas-shift are currently the most feasible and scalable technologies for hydrogen generation from waste plastics, with pyrolysis operating in an oxygen-free environment and gasification in the presence of steam, though both require high energy inputs. Aqueous phase reforming operates at moderate temperatures and pressures, making it suitable for oxygenated plastics, but it faces challenges related to feedstock limitations, catalyst costs and deactivation. Photoreforming and electrocatalytic reforming are emerging, sustainable methods that use sunlight and electricity, respectively, to convert plastics into hydrogen. Still, they suffer from low efficiency, scalability issues, and limitations to specific plastic types like oxygenated polymers. The challenges and solutions to commercializing plastic-to-hydrogen technologies, drawing on global industrial case studies have been outlined. Maximizing hydrogen productivity and selectivity, minimizing energy consumption, and ensuring stable operation and scaleup of plastic recycling are crucial parameters for achieving commercial viability.

Selective Electrocatalytic Production of Formic Acid from Plastic Waste Using a Nickel Metal-Organic Framework Constructed from a Biomass-Derived Ligand

A novel nickel-based metal organic framework (MOF) [Ni(FDC)(CH3OH)1.5(H2O)0.5](H2O)0.35 (UOW-6) utilizing biomass-derived 2,5-furan dicarboxylate (FDC) as a ligand is reported as an electrocatalyst for anodic ethylene glycol (EG) oxidation with cathodic hydrogen evolution. The MOF structure was analyzed using single crystal X-ray-diffraction, thermogravimetric analysis (TGA) and thermodiffractometry, to establish its structure and verify phase purity. The material was dropcast on carbon fiber paper as a catalyst, and by using a three-electrode system, UOW-6 requires only 1.47 V to attain a current density of 50 mA cm-2. During oxidation of the EG, UOW-6 shows unprecedented selectivity towards formic acid with a Faradaic efficiency of 94 % and remarkable stability over 20 days. The combination of electrochemical measurements and in situ Raman confirmed in situ formed NiOOH at the surface of UOW-6 as the catalytically active sites for EG oxidation. This work not only presents a pioneering application of FDC-based MOFs for polyethylene terephthalate (PET) upcycling but also underscores the potential of electrocatalysis in advancing sustainable plastic valorization strategies.

Stable Ni(II) sites in Prussian blue analogue for selective, ampere-level ethylene glycol electrooxidation

The industrial implementation of coupled electrochemical hydrogen production systems necessitates high power density and high product selectivity for economic viability and safety. However, for organic nucleophiles (e.g., methanol, urea, and amine) electrooxidation in the anode, most catalytic materials undergo unavoidable reconstruction to generate high-valent metal sites under harsh operation conditions, resulting in competition with oxygen evolution reaction. Here, we present unique Ni(II) sites in Prussian blue analogue (NiFe-sc-PBA) that serve as stable, efficient and selective active sites for ethylene glycol (EG) electrooxidation to formic acid, particularly at ampere-level current densities. Our in situ/operando characterizations demonstrate the robustness of Ni(II) sites during EG electrooxidation. Molecular dynamics simulations further illustrate that EG molecule tends to accumulate on the NiFe-sc-PBA surface, preventing hydroxyl-induced reconstruction in alkaline solutions. The stable Ni(II) sites in NiFe-sc-PBA anodes exhibit efficient and selective EG electrooxidation performance in a coupled electrochemical hydrogen production flow cell, producing high-value formic acid compared to traditional alkaline water splitting. The coupled system can continuously operate at stepwise ampere-level current densities (switchable 1.0 or 1.5 A cm-2) for over 500 hours without performance degradation.

Pulsed electrosynthesis of glycolic acid through polyethylene terephthalate upcycling over a mesoporous PdCu catalyst

Electrocatalytic upcycling of polyethylene terephthalate (PET) plastics offers a promising and sustainable route that not only addresses serious waste pollution but also produces high value-added chemicals. Despite some important achievements, their activity and selectivity have been slower than needed. In this work, pulsed electrocatalysis is employed to engineer chemisorption properties on a lamellar mesoporous PdCu (LM-PdCu) catalyst, which delivers high activity and stability for selective electrosynthesis of high value-added glycolic acid (GA) from PET upcycling under ambient conditions. LM-PdCu is synthesized by in situ nucleation and attachment strategy along assembled lamellar templates, whose stacked morphology and lamellar mesoporous structure kinetically accelerate selective desorption of GA and expose fresh active sites of metal catalysts for continuous electrocatalysis at pulsed mode. This strategy thus delivers GA Faraday efficiency of >92% in wide potential windows, yield rate of reaching 0.475 mmol cm-2 h-1, and cycling stability of exceeding 20 cycles for electrocatalytic PET upcycling. Moreover, pulsed electrocatalysis discloses good electrocatalytic performance for scaled-up GA electrosynthesis from real bottle waste plastics. This work presents a sustainable route for selective electrosynthesis of value-added chemicals through upcycling of various waste feedstocks.

Circular Economy and Chemical Conversion for Polyester Wastes

Polyester waste in the environment threatens public health and environmental ecosystems. Chemical recycling of polyester waste offers a dual solution to ensure resource sustainability and ecological restoration. This minireview highlights the traditional recycling methods and novel recycling strategies of polyester plastics. The conventional strategy includes pyrolysis, carbonation, and solvolysis of polyesters for degradation and recycling. Furthermore, the review delves into exploring emerging technologies including hydrogenolysis, electrocatalysis, photothermal, photoreforming, and enzymatic for upcycling polyesters. It emphasizes the selectivity of products during the polyester conversion process and elucidates conversion pathways. More importantly, the separation and purification of the products, the life cycle assessment, and the economic analysis of the overall recycling process are essential for evaluating the environmental and economic viability of chemical recycling of waste polyester plastics. Finally, the review offers perspective into the future challenges and developments of chemical recycling in the polyester economy.

Incorporating Ordered Indium Sites into Rhodium for Ultra-Low Potential Electrocatalytic Conversion of Ethylene Glycol to Glycolic Acid

The upcycling of polyethylene terephthalate (PET)-derived ethylene glycol (EG) to glycolic acid (GA, a biodegradable polymer monomer) via electrocatalysis not only produces valuable chemicals but also mitigates plastic pollution. However, the current reports for electrooxidation of EG-to-GA usually operate at reaction potentials of >1.0 V vs reversible hydrogen electrode (RHE), much higher than the theoretical potential (0.065 V vs RHE), resulting in substantial energy wastage. Herein, body-centered cubic RhIn intermetallic compounds (IMCs) anchored on carbon support (denoted as RhIn/C) are synthesized, which shows excellent performance for the EG-to-GA with an onset potential of only 0.35 V vs RHE, lower than the values reported in current literature. The catalyst also possesses satisfactory GA selectivity (85% at 0.65 V vs RHE). Experimental results combined with density functional theory calculations demonstrate that RhIn IMCs enhance the adsorption of EG and OH-, facilitating the generation of reactive oxygen species and thereby improving catalytic performance. RhIn/C also exhibits excellent electrocatalytic performance for hydrogen evolution reaction, ensuring that it can be used as a bifunctional catalyst in the two-electrode system for EG electrooxidation coupled with hydrogen production. This work opens new avenues for reducing the energy consumption of electrocatalytic upcycling of PET-derived EG and clean energy production.

High-Performance Electrocatalysts of Potassium Lactate Oxidation for Hydrogen and Solid Potassium Acetate Production

With the increasing use of polylactic acid (PLA), more attention is turning to its post-treatment. Current methods such as natural decomposition, composting, and incineration are limited by significant carbon dioxide emissions and resource waste. Here, an efficient electrocatalytic conversion approach is presented to transform PLA waste into high-value chemicals, particularly potassium acetate (AA-K). By combining experimental and theoretical calculation, a high-performance catalyst Ni(Co)OOH is developed, which exhibits a current density of 403 mA cm⁻2 at 1.40 V (vs RHE) with 96% Faraday efficiency for AA-K in the electrooxidation of potassium lactate (LA-K, the product of PLA degradation in KOH). Through in situ spectroscopy techniques and density functional theory calculations, the structural regulation of the catalyst, and reaction pathways of the electrooxidation are elucidated. Further experiments demonstrate the superior catalytic performance of the Ni(Co)OOH catalyst in an industrial-scale tandem system. In 2 h of electrolysis, 320 g of PLA waste produces 232 L of H₂, yielding 1200 g of AA-K with 97% purity after neutralization and drying. The system demonstrates high conversion efficiency (approaching 97%) for diverse real PLA waste forms, including powder, cups, fibers, and cloth. This research provides a scalable and sustainable approach for PLA waste upcycling.

Electrocatalytic Conversion of Glucose into Renewable Formic Acid Using "Electron-Withdrawing" MoO3 Support under Mild Conditions

Electrocatalysis is a sustainable and effective approach to produce value-added chemical commodities from biomass, where highly effective catalyst is required. Since transition metal hydroxide is a feasible catalyst for electrochemical biomass conversion, rational optimization of its electrocatalytic activity is highly desired. Herein, electrocatalytic activity of glucose oxidation is significantly optimized by reducing the electron density at Ni active sites, which is achieved by depositing Ni(OH)2 at "electron-withdrawing" MoO3 support (Ni(OH)2MoO3-x). As results, the formation of active sites (NiOOH) and the adsorption of glucose are simultaneously facilitated in Ni(OH)2MoO3-x, which effectively converts glucose to formic acid (FA) with remarkable yield and Faraday efficiency (≈90.5 and 98%, respectively), far superior to conventional β-Ni(OH)2 catalyst (≈22.5 and 58.9%, respectively). In addition to a novel strategy for efficient FA production from glucose, this work offers valuable insights into the rational optimization of electrocatalytic oxidation of biomass-based substrates.

Selective Asymmetric Hydrogenation of Waste Polyethylene Terephthalate via Controlled Sorption through Precisely Tuned Moderate Acid Sites

The partial hydrogenation of waste polyethylene terephthalate (PET) offers a great opportunity to produce valuable chemicals, yet achieving precise catalytic control remains challenging. Herein, for the first time, we realized one-pot selective hydrogenation of waste PET to p-toluic acid (p-TA) with a record-high yield of 53.4%, alongside a 36.4% yield of p-xylene (PX), using a specially designed PtW/MCM-48 catalyst. Mechanistic investigations revealed that the exceptional catalytic performance arises from synergistic interaction between Pt nanoparticles and WOx species. Low-valent WOx enhances Pt dispersion, while Pt stabilizes WOx as low-polymerized polytungstates. The moderate acidity of PtW1.5/MCM-48 ensures controlled desorption of p-TA, preventing overhydrogenation to PX. The catalyst demonstrated robust performance with real-world PET waste. Life cycle assessment and technical and economic evaluation further highlight its practical feasibility. This study establishes a sustainable pathway for PET chemical upcycling and provides a framework for designing advanced catalysts for selective hydrogenation reactions, addressing critical challenges in circular chemistry and plastic waste management.

Surface Coverage Tuning for Suppressing Over-Oxidation: A Case of Photoelectrochemical Alcohol-to-Aldehyde/Ketone Conversion

Suppressing over-oxidation is a crucial challenge for various chemical intermediate synthesis in heterogeneous catalysis. The distribution of oxidative species and the substrate coverage, governed by the direction of electron transfer, are believed to influence the oxidation extent. In this study, we presented an experimental realization of surface coverage modulation on a photoelectrode using a photo-induced charge activation method. Through the surface coverage modulation, both pre-oxidized alcohol substrates and surface coverage were increased, which not only improved the reaction kinetics but also suppressed the over-oxidation of the generated aldehydes/ketones. As a demonstration, the Faradaic efficiency for the conversion of glycerol to dihydroxyacetone increased from 31.8 % to 46.8 % (with selectivity rising from 47.6 % to 71.3 %), from 73.4 % to 87.8 % for benzyl alcohol to benzyl aldehyde (selectivity increasing from 76.7 % to 92.4 %) and from 4.2 % to 53.6 % for ethylene glycol to glycolaldehyde (selectivity increasing from 6.2 % to 62.7 %). Our findings offer a promising strategy for the production of high-value carbon products in heterogeneous catalysis.

Emerging Biochemical Conversion for Plastic Waste Management: A Review

In recent years, vast amounts of plastic waste have been released into the environment worldwide, posing a severe threat to human health and ecosystems. Despite the partial success of traditional plastic waste management technologies, their limitations underscore the need for innovative approaches. This review provides a comprehensive overview of recent advancements in chemical and biological technologies for converting and utilizing plastic waste. Key topics include the technical parameters, characteristics, processes, and reaction mechanisms underlying these emerging technologies. Additionally, the review highlights the importance of conducting economic analyses and life cycle assessments of these emerging technologies, offering valuable insights and establishing a robust foundation for future research. By leveraging the literature from the last five years, this review explores innovative chemical approaches, such as hydrolysis, hydrogenolysis, alcoholysis, ammonolysis, pyrolysis, and photolysis, which break down high-molecular-weight macromolecules into oligomers or small molecules by cracking or depolymerizing specific chemical groups within plastic molecules. It also examines innovative biological methods, including microbial enzymatic degradation, which employs microorganisms or enzymes to convert high-molecular-weight macromolecules into oligomers or small molecules through degradation and assimilation mechanisms. The review concludes by discussing future research directions focused on addressing the technological, economic, and scalability challenges of emerging plastic waste management technologies, with a strong commitment to promoting sustainable solutions and achieving lasting environmental impact.

Progress on Photo-, Electro-, and Photoelectro-Catalytic Conversion of Recalcitrant Polyethylene, Polypropylene, and Polystyrene - A Review

Recalcitrant waste plastics such a polyethylene, polypropylene, and polystyrene are difficult to recycle and are mostly disposed of in landfills and eventually leached into the environmental as micro- and nano-plastics. This review explores how photo-, electro-, and combined photoelectro-catalytic processes can assist in the degradation and upcycling of waste plastic into different chemicals and mitigate their release to the environment. In this work, we discuss how the different reaction mechanisms proceed, explore the current relevant literature, and highlight the developments needed to advance the field.

Hydrogenating Polyethylene Terephthalate into Degradable Polyesters

The recycling and upcycling of polyethylene terephthalate (PET), the most widely used polyester plastic globally, has attracted growing attention concerning its disposal as non-degradable waste in the natural environment. Transforming end-of-life PET into (bio)degradable polyester offers a novel approach to managing its waste. In this study, we introduce a simple process capable of converting waste PET into degradable polyester, polyethylene terephthalate-polyethylene-1,4-cyclohexanedicarboxylate (PET-PECHD), by partly hydrogenating the aromatic rings (x) into aliphatic ones (y). The polyesters with variable x/y compositions ranging from 100/0 to 0/100 can be achieved, and the molecular weight (Mw) can be maintained when x/y >87/13 due to the nonobvious depolymerization. Pronounced depolymerization would occur with deeper hydrogenation, which generates a blend of PET-PECHD and polyethylene-1,4-cyclohexanedicarboxylate (PECHD) with lower Mw, and finally a single-type polymer PECHD. The PET-PECHD demonstrates comparable thermal stability and mechanical strength compared to PET, along with superior extensibility, barrier properties, and (bio)degradability in acidic, alkaline solutions, and moist soil. This research highlights the potential for cost-effective, large-scale production of degradable polyester from real-life plastic waste.

Rapid Surface Reconstruction of Amorphous-Crystalline NiO for Industrial-Scale Electrocatalytic PET Upcycling

The conversion of plastic waste into valuable chemicals through innovative and selective nano-catalysts offers significant economic benefits and positive environmental impacts. However, our current understanding of catalyst design capable of achieving industrial-grade current densities is limited. Herein, we develop a self-supported amorphous-crystalline NiO electrocatalyst for the electrocatalytic upcycling of polyethylene terephthalate (PET) into formate and hydrogen fuel. The catalyst achieves an industrial current density of over 1 A cm-2 at 1.5 V vs. RHE, with an 80 % Faradaic efficiency and a formate production rate of 7.16 mmol cm-2 h-1. In situ Raman spectroscopy, X-ray absorption spectroscopy, and density functional theory calculations reveal that the rapid transformation of amorphous-crystalline NiO into γ-NiOOH at the amorphous-crystalline interface provides a thermodynamic advantage for formate desorption, leading to the high activity required for industrial applications, which is challenging to achieve for fully crystalline NiO. A techno-economic analysis indicates that recycling waste PET using this catalytic process could generate a profit of $582 per ton. This work presents a cost-effective and highly efficient approach to promoting the sustainable utilization of waste PET.

Selective Recycling of Mixed Polyesters via Heterogeneous Photothermal Catalysis

The selective recycling of mixed plastic wastes with similar structural units is challenging. While heterogeneous catalysis shows potential for selective recycling, challenges such as complex mass transfer at multiphase interfaces and unclear catalytic mechanisms have slowed progress. In this study, a breakthrough in recycling mixed polyester wastes is introduced using heterogeneous photothermal catalysis. By adding co-solvents, the difficulties associated with multiphase interfacial mass transfer are overcome. Grain boundary (GB)-rich CeO2 photothermal catalysts are used to selectively glycolyze mixed poly(ethylene terephthalate) (PET) and poly(bisphenol A carbonate) (PC) plastics into bisphenol A (BPA) and bis(2-hydroxyethyl) terephthalate (BHET), achieving yields of 97.8% and 93.4%, respectively. The high concentration of oxygen vacancies in GB-rich CeO2 catalysts adjusts the adsorption energy of intermediates, leading to more selective and efficient depolymerization compared to GB-poor CeO2 catalysts. The economic and environmental analysis demonstrates that this process, which utilizes heterogeneous photothermal catalysis, provides significant energy savings and carbon reduction, representing a major advancement in mixed plastic waste recycling.

Recent Advances and Perspectives on Coupled Water Electrolysis for Energy-Saving Hydrogen Production

Overall water splitting (OWS) to produce hydrogen has attracted large attention in recent years due to its ecological-friendliness and sustainability. However, the efficiency of OWS has been forced by the sluggish kinetics of the four-electron oxygen evolution reaction (OER). The replacement of OER by alternative electrooxidation of small molecules with more thermodynamically favorable potentials may fundamentally break the limitation and achieve hydrogen production with low energy consumption, which may also be accompanied by the production of more value-added chemicals than oxygen or by electrochemical degradation of pollutants. This review critically assesses the latest discoveries in the coupled electrooxidation of various small molecules with OWS, including alcohols, aldehydes, amides, urea, hydrazine, etc. Emphasis is placed on the corresponding electrocatalyst design and related reaction mechanisms (e.g., dual hydrogenation and N-N bond breaking of hydrazine and C═N bond regulation in urea splitting to inhibit hazardous NCO- and NO- productions, etc.), along with emerging alternative electrooxidation reactions (electrooxidation of tetrazoles, furazans, iodide, quinolines, ascorbic acid, sterol, trimethylamine, etc.). Some new decoupled electrolysis and self-powered systems are also discussed in detail. Finally, the potential challenges and prospects of coupled water electrolysis systems are highlighted to aid future research directions.

Self-assembled Gap-Rich PdMn Nanofibers with High Mass/Electron Transport Highways for Electrocatalytic Reforming of Waste Plastics

Innovating nanocatalysts with both high intrinsic catalytic activity and high selectivity is crucial for multi-electron reactions, however, their low mass/electron transport at industrial-level currents is often overlooked, which usually leads to low comprehensive performance at the device level. Herein, a Cl-/O2 etching-assisted self-assembly strategy is reported for synthesizing a self-assembled gap-rich PdMn nanofibers with high mass/electron transport highway for greatly enhancing the electrocatalytic reforming of waste plastics at industrial-level currents. The self-assembled PdMn nanofiber shows excellent catalytic activity in upcycling waste plastics into glycolic acid, with a high current density of 223 mA cm-2@0.75 V (vs RHE), high selectivity (95.6%), and Faraday efficiency (94.3%) to glycolic acid in a flow electrolyzer. Density functional theory calculation, X-ray absorption spectroscopy combined with in situ electrochemical Fourier transform infrared spectroscopy reveals that the introduction of highly oxophilic Mn induces a downshift of the d-band center of Pd, which optimizes the adsorption energy of the reaction intermediates on PdMn surface, thereby facilitating the desorption of glycolic acid as a high-value product. Computational fluid dynamics simulations confirm that the gap-rich nanofiber structure is conducive for mass transfer to deliver an industrial-level current.

Photoelectrochemical Ethylene Glycol Oxidization Coupled with Hydrogen Generation Using Metal Oxide Photoelectrodes

Photoelectrochemical (PEC) water splitting represents a promising approach for harnessing solar energy and transforming it into storable hydrogen. However, the complicated 4-electron transfer process of water oxidation reaction imposes kinetic limitations on the overall efficiency. Herein, we proposed a strategy by substituting water oxidation with the oxidation of ethylene glycol (EG), which is a hydrolysis byproduct of polyethylene terephthalate (PET) plastic waste. To achieve this, we developed and synthesized BiVO4/NiCo-LDH photoanodes capable of achieving a high Faradaic efficiency (FE) exceeding 85 % for the oxidation of EG to formate in a strongly alkaline environment. The reaction mechanism was further elucidated using in situ FTIR spectroscopy. Additionally, we successfully constructed an unassisted PEC device for EG oxidation and hydrogen generation by pairing the translucent Mo : BiVO4/NiCo-LDH photoanode with a state-of-the-art Cu2O photocathode, resulting in an approximate photocurrent density of 2.3 mA/cm2. Our research not only offers a PEC pathway for converting PET plastics into valuable chemicals but also enables simultaneous hydrogen production.

Cation-Vacancy Engineering in Cobalt Selenide Boosts Electrocatalytic Upcycling of Polyester Thermoplastics at Industrial-Level Current Density

The past decades have witnessed the increasing accumulation of plastics, posing a daunting environmental crisis. Among various solutions, converting plastics into value-added products presents a significant endeavor. Here, an electrocatalytic upcycling route that efficiently converts waste poly(butylene terephthalate) plastics into high-value succinic acid with high Faradaic efficiency of 94.0% over cation vacancies-rich cobalt selenide catalyst is reported, showcasing unprecedented activity (1.477 V vs. RHE) to achieve an industrial-level current density of 1.5 A cm-2, and featuring a robust operating durability (≈170 h). In particular, when combining butane-1,4-diol monomer oxidation (BOR) with hydrogen evolution using the cation vacancy-engineered cobalt selenide as bifunctional catalyst, a relatively low cell voltage of 1.681 V is required to reach 400 mA cm-2, manifesting an energy-saving efficiency of ≈15% compared to pure water splitting. The mechanism and reaction pathways of BOR over the vacancies-rich catalyst are first revealed through theoretical calculations and in-situ spectroscopic investigations. The generality of this catalyst is evidenced by its powerful electrocatalytic activity to other polyester thermoplastics such as poly(butylene succinate) and poly(ethylene terephthalate). These electrocatalytic upcycling strategies can be coupled with the reduction of small molecules (e.g., H2O, CO2, and NO3 -), shedding light on energy-saving production of value-added chemicals.

Electrosynthesis of ethylene glycol from biomass glycerol

Ethylene glycol, a widely used chemical, has a large global capacity exceeding 40 million tons per year. Nevertheless, its production is heavily reliant on fossil fuels, resulting in substantial CO2 emissions. Herein, we report an approach for electrochemically producing ethylene glycol from biomass glycerol. This process involves glycerol electrooxidation to glycolaldehyde at anode, which is subsequently electro-reduced to ethylene glycol at cathode. While the anode reaction has been reported, the cathode reaction remains a challenge. An electrodeposited electrode with metallic Cu catalyst enables us to achieve glycolaldehyde-to-ethylene glycol conversion with an exceptional faradaic efficiency of about 80%. Experimental and theoretical studies reveal that metallic Cu catalyst facilitates the C=O activation, promoting glycolaldehyde hydrogenation into ethylene glycol. We further assemble a zero-gap electrolyzer and demonstrate ethylene glycol electrosynthesis from glycerol to give a decent production rate of 1.32 mmol cm-2 h-1 under a 3.48 V cell voltage. The carbon intensity assessment based on a valid assumption reveals that our strategy may reduce CO2 emissions by over 80 million tons annually compared to conventional fossil fuel routes.

Advanced systems for enhanced CO2 electroreduction

Carbon dioxide (CO2) electroreduction has extraordinary significance in curbing CO2 emissions while simultaneously producing value-added chemicals with economic and environmental benefits. In recent years, breakthroughs in designing catalysts, optimizing intrinsic activity, developing reactors, and elucidating reaction mechanisms have continuously driven the advancement of CO2 electroreduction. However, the industrialization of CO2 electroreduction remains a challenging task, with high energy consumption, high costs, limited reaction products, and restricted application scenarios being the issues that urgently need to be addressed. To accelerate the progress of CO2 electroreduction towards practical application, this review shifts the research focus from catalysts to aspects such as reactions and systems, aiming to improve reaction efficiency, reduce technical costs, expand the range of products, and enhance selectivity, offering readers a new perspective. In particular, innovative and specific design strategies such as CO2 reduction coupled with alternative oxidation, co-reduction reaction of CO2 and C/N/O/S-containing species, cascade systems, and integrated CO2 capture and reduction systems are discussed in detail. Additionally, personal views on the opportunities and future challenges of the aforementioned innovative strategies are provided, offering new insights for the future research and development of CO2 electroreduction.

Advanced Catalysts for the Chemical Recycling of Plastic Waste

Plastic products bring convenience to various aspects of the daily lives due to their lightweight, durability and versatility, but the massive accumulation of post-consumer plastic waste is posing significant environmental challenges. Catalytic methods can effectively convert plastic waste into value-added feedstocks, with catalysts playing an important role in regulating the yield and selectivity of products. This review explores the latest advancements in advanced catalysts applied in thermal catalysis, microwave-assisted catalysis, photocatalysis, electrocatalysis, and enzymatic catalysis reaction systems for the chemical recycling of plastic waste into valuable feedstocks. Specifically, the pathways and mechanisms involved in the plastics recycling process are analyzed and presented, and the strengths and weaknesses of various catalysts employed across different reaction systems are described. In addition, the structure-function relationship of these catalysts is discussed. Herein, it is provided insights into the design of novel catalysts applied for the chemical recycling of plastic waste and outline challenges and future opportunities in terms of developing advanced catalysts to tackle the "white pollution" crisis.

Chemical transformation of polyurethane into valuable polymers

Polyurethanes are an important class of synthetic polymers, widely used in a variety of applications ranging from everyday items to advanced tools in societal infrastructure. Their inherent cross-linked structure imparts exceptional durability and flexibility, yet this also complicates their degradation and recycling. Here we report a heterogeneous catalytic process that combines methanolysis and hydrogenation with a CO2/H2 reaction medium, effectively breaking down PU waste consisting of urethane and ester bonds into valuable intermediates like aromatic diamines and lactones. These intermediates are then converted into functional polymers: polyimide (PI), noted for its exceptional thermal and electrical insulation, and polylactone (P(BL-co-CL)), a biodegradable alternative to traditional plastics. Both polymers exhibit enhanced performance compared to existing commercial products. This approach not only contributes to the valorization of plastic waste but also opens new avenues for the creation of high-performance materials.

Catalytic oxidation upcycling of polyethylene terephthalate to commodity carboxylic acids

Catalytic upcycling of polyethylene terephthalate (PET) into high-value oxygenated products is a fascinating process, yet it remains challenging. Here, we present a one-step tandem strategy to realize the thermal catalytic oxidation upcycling of PET to terephthalic acid (TPA) and high-value glycolic acid (GA) instead of ethylene glycol (EG). By using the Au/NiO with rich oxygen vacancies as catalyst, we successfully accelerate the hydrolysis of PET, accompanied by obtaining 99% TPA yield and 87.6% GA yield. The results reveal that the oxygen vacancies in NiO (NiO-Ov) support tend to adsorb hydrolysis product TPA, preferentially ensuring the strong adsorption of EG at the Au-NiO interface. Moreover, during the EG oxidation process, the Au-NiO interface, composed of two types of structures, quasi "AuNi alloy" and NiO-Ov, simultaneously promote the C-H bond activation, where Ni in "AuNi alloy" exhibits an oxytropism effect to anchor the C = O bond of the intermediate, while the residual O in NiO-Ov pillages the H in the C-H bond. Such Au/NiO catalyst is further extended to promote the thermal catalytic oxidation upcycling of other polyethylene glycol esters to GA with excellent catalytic performance.

Metabolic engineering of Escherichia coli for upcycling of polyethylene terephthalate waste to vanillin

Polyethylene terephthalate (PET) waste presents a significant environmental challenge due to its durability and resistance to degradation. Innovative approaches for upcycling PET waste into high-value chemicals can mitigate these issues while contributing to a circular economy. In this study, we developed a multi-enzyme cascade system in E. coli to convert PET-derived monomer terephthalic acid (TPA) into vanillin (VAN). The metabolic engineering approach was then employed to increase VAN production, including 1) inhibition of VAN degradation by knocking out endogenous aldehyde reductases and alcohol dehydrogenases and 2) enhancement of TPA uptake by modifying membrane proteins to increase cell permeability. The engineered E. coli demonstrated a VAN production of 658.55 mg/L from 1992 mg/L of TPA with a molar conversion rate of 71.1 %, representing the highest production of VAN using TPA as the substrate. Additionally, the engineered E. coli effectively converted post-consumer PET waste into VAN under mild conditions, with the highest production of 259.2 mg/L in 20× diluted PET hydrolysates, highlighting its potential for application in PET waste upcycling. This approach not only provides an environmentally friendly alternative to traditional chemical synthesis but also offers substantial economic benefits by transforming low-value waste into high-value chemicals.

Upcycling of waste polyesters for the development of a circular economy

The rapidly increasing production and widespread application of plastics have brought convenience to our lives, but they have consumed a huge amount of nonrenewable fossil energy, leading to additional CO2 emissions and generation of an enormous amount of plastic waste (also called white pollution). Chemical recycling and upcycling of waste plastic products (also called waste plastic refineries) into recycled monomers and/or valuable chemicals can decrease the dependence on fossil energy and/or reduce the emission of CO2, enabling the full utilization of carbon resources for the development of a circular economy. Polyesters, a vital class of plastics, are ideal feedstocks for chemical recycling due to the easily depolymerizable ester bonds compared to polyolefins. Among them, polyethylene terephthalate (PET) is the most widely used product, making its chemical recycling to a circular carbon resource a hot topic with significant concerns. In this feature article, recent progress in depolymerization of waste polyesters (PET and/or PET-containing materials) and the subsequent upgrading of depolymerized monomers (or intermediates) to valuable chemicals was reviewed and prospected. Newly reported technologies, such as thermal catalysis, photocatalysis, electrocatalysis, and biocatalysis, were discussed. The achievements, challenges, and potential of industrial applications of chemical recycling of polyesters were addressed.

Selective Oxidation of Polyesters via PdCu-TiO2 Photocatalysts in Flow

Catalytic upcycling of plastic wastes offers a sustainable circular economy. Selective conversion of the most widely used polyester, polyethylene terephthalate (PET), under ambient conditions is practically attractive because of low energy consumption and carbon footprint. Here, we report selective, aerobic conversion of PET in a flow reactor using TiO2 photocatalyst modified with atomic Pd and metallic PdCu (Pd1Cu0.4-TiO2) under ambient conditions. We demonstrate that atomically synergistic Pd1Cu0.4-TiO2 exhibits a formate evolution of 4707 μmol g-1 h-1 with a selectivity of 92.3% together with trace COx released. Importantly, we show that this corresponds to 10-103 times greater activity than reported photocatalytic systems. We confirm that synergy between atomic Pd and metallic PdCu boosts directional charge transfer and oxygen-induced C-C cleavage and inhibits product decomposition. We conclude that photocatalytic waste plastic-to-chemical conversion is sustainable via targeted engineering of atomically synergistic catalysts and reaction systems.

Self-sacrificing and self-supporting biomass carbon anode-assisted water electrolysis for low-cost hydrogen production

Electrooxidation of renewable and CO2-neutral biomass for low-cost hydrogen production is a promising and green technology. Various biomass platform molecules (BPMs) oxidation assisted hydrogen production technologies have obtained noticeable progress. However, BPMs anodic oxidation is highly dependent on electrocatalysts, and the oxidation mechanism is ambiguous. Meanwhile, the complexity and insolubility of natural biomass severely constrain the efficient utilization of biomass resources. Here, we develop a self-sacrificing and self-supporting carbon anode (SSCA) using waste corncobs. The combined results from multiple characterizations reveal that the structure-property-activity relationship of SSCA in carbon oxidation reaction (COR). Theoretical calculations demonstrate that carbon atoms with a high spin density play a pivotal role in reducing the adsorption energy of the reactive oxygen intermediate (*OH) during the transition from OH- to *OH, thereby promoting COR. Additionally, the HER||COR system allows driving a current density of 400 [Formula: see text] at 1.24 V at 80 °C, with a hydrogen production electric consumption of 2.96 kWh Nm-3 (H2). The strategy provides a ground-breaking perspective on the large-scale utilization of biomass and low-energy water electrolysis for hydrogen production.

Electrochemical Upgrading of Waste Polylactic Acid Plastic for the Coproduction of C2 Chemicals and Green Hydrogen

Tandem alkali-catalyzed hydrolysis and alkaline electrolysis have gradually become appealing avenues for the reformation of polyester plastics into high-value-added chemicals and green hydrogen with remarkable environmental and economic benefits. In this study, an electrochemical upcycling strategy was developed for the electrocatalytic oxidation of polylactic acid (PLA) hydrolysate into valued C2 chemicals (i.e., acetate) and hydrogen fuel using N, P-doped CuOx nanowires (NW) supported on nickel foam (NF) as the electrocatalyst. This 3D well-integrated catalyst was easily prepared from a Cu(OH)2 NW/NF precursor with Saccharomycetes as a green and safe P and N source. The electrocatalyst can efficiently catalyze the lactate monomer derived from the hydrolysis of PLA waste to acetate with high selectivity and exhibits a lower onset potential for the lactate oxidation reaction (LOR) than for water oxidation, saving 224 mV to deliver a current density of 30 mA/cm2. The experimental results reveal that the plausible pathway of the LOR on these CuOx NW involves oxidation and subsequent decarboxylation. Divalent copper species have been verified to be active sites for LOR via in situ Raman spectroscopy.

Energy-Saving Ambient Electrosynthesis of Nylon-6 Precursor Coupled with Electrocatalytic Upcycling of Polyethylene Terephthalate

Cyclohexanone oxime is an important intermediate in the chemical industry, especially for the manufacture of nylon-6. The traditional cyclohexanone oxime production strongly relies on cyclohexanone-hydroxylamine and cyclohexanone ammoxidation processes, which require harsh reaction conditions and consume considerable amounts of energy. Herein, direct electrosynthesis of cyclohexanone oxime is reported from environmental pollutants nitrite and cyclohexanone with almost 100% yield by using low-cost Cu2Se nanosheets as electrocatalysts. Combination of in situ Fourier transform infrared spectroscopy and theoretical calculations verifies that the p-d orbital hybridization between Cu and Se elements could synergistically optimize the surface electronic structure and enable improved adsorption and formation of the key active N intermediate NH2OH*, thereby enhancing cyclohexanone/nitrite-to-cyclohexanone oxime conversion over the Cu2Se nanosheets. Based on these, an efficient asymmetric co-electrolysis system is further demonstrated by coupling cyclohexanone/nitrite-to-cyclohexanone oxime conversion with the upcycling of polyethylene terephthalate plastics, achieveing energy-saving simultaneously production of value-added products (cyclohexanone oxime and glycolic acid).

Electrocatalytic Valorization of Nitrate and Polyester Plastic for Simultaneous Production of Ammonia and Glycolic Acid

Electrochemical upcycling of nitrate and polyester plastic into valuable products is an ideal solution to realize the resource utilization. Here, the co-production of ammonia (NH3) and glycolic acid (GA) via electrochemical upcycling of nitrate and polyethylene terephthalate (PET) plastics over mesoporous Pd3Au film on Ni foam (mPd3Au/NF), which is synthesized by micelle-assisted replacement method, is proposed. The mPd3Au/NF with well-developed mesoporous structure provides abundant active sites and facilitated transfer channels and strong electronic effect. As such, the mPd3Au/NF exhibits high Faraday efficiencies of 97.28% and 95.32% at 0.9 V for the formation of NH3 and GA, respectively. Theoretical results indicate that the synergistic effect of Pd and Au can optimize adsorption energy of key intermediates *NOH and *OCH2-CH2OH on active sites and increase bond energy of C─C band, thereby improving the activity and selectivity for the formation of NH3 and GA. This work proposes a promising strategy for the simultaneous conversation of nitrate and PET plastic into high-value NH3 and GA.

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02 mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

Facilitating Formate Selectivity via Optimizing eg* Band Broadening in NiMn Hydroxides for Ethylene Glycol Electro-Oxidation

Ethylene glycol electro-oxidation reaction (EGOR) on nickel-based hydroxides (Ni(OH)2) represents a promising strategy for generating value-added chemicals, i.e. formate and glycolate, and coupling water-electrolytic hydrogen production. The high product selectivity was one of the most significant area of polyols electro-oxidation process. Yet, developing Ni(OH)2-based EGOR electrocatalyst with highly selective product remains a challenge due to the unclear cognition about the EGOR mechanism. Herein, Mn-doped Ni(OH)2 catalysts were utilized to investigate the EGOR mechanism. Experimental and calculation results reveal that the electronic states of eg* band play an important role in the catalytic performance and the product selectivity for EGOR. Broadening the eg* band could effectively enhance the adsorption capacity of glyoxal intermediates. On the other hand, this enhanced adsorption could lead to reduced side reactions associated with glycolate formation, simultaneously promoting the cleavage of C-C bonds. Consequently, the selectivity for formate was notably augmented by these enhancements. This work offers new insights into the regulation of catalyst electronic states for improving polyol electrocatalytic activity and product selectivity.

Membrane-Free Electrocatalytic Co-Conversions of PBS Waste Plastics and Maleic Acid into High-Purity Succinic Acid Solid

Plastic pollution, an increasingly serious global problem, can be addressed through the full lifecycle management of plastics, including plastics recycling as one of the most promising approaches. System design, catalyst development, and product separation are the keys in improving the economics of electrocatalytic plastics recycling. Here, a membrane-free co-production system was devised to produce succinic acid (SA) at both anode and cathode respectively by the co-electrolysis of polybutylene succinate (PBS) waste plastics and biomass-derived maleic acid (MA) for the first time. To this end, Cr3+-Ni(OH)2 electrocatalyst featuring much enhanced 1,4-butanediol (BDO) oxidation reaction (BOR) activity has been synthesized and the role of doped Cr has been revealed as an "electron puller" to accelerate the rate-determining step (RDS) in the Ni2+/Ni3+ cycling. Impressively, an extra-high SA production rate of 3.02 g h-1 and ultra-high apparent Faraday efficiency towards SA (FEapparent=181.5 %) have been obtained. A carbon dioxide-assisted sequential precipitation approach has been developed to produce high-purity SA and byproduct NaHCO3 solids. Preliminary techno-economic analysis demonstrates that the reported system is economically profitable and promising for future industrial applications.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Wood-Structured Nanomaterials as Highly Efficient, Self-Standing Electrocatalysts for Water Splitting

Electrocatalytic water splitting (EWS) driven by renewable energy is widely considered an environmentally friendly and sustainable approach for generating hydrogen (H2), an ideal energy carrier for the future. However, the efficiency and economic viability of large-scale water electrolysis depend on electrocatalysts that can efficiently accelerate the electrochemical reactions taking place at the two electrodes. Wood-derived nanomaterials are well-suited for serving as EWS catalysts because of their hierarchically porous structure with high surface area and low tortuosity, compositional tunability, cost-effectiveness, and self-standing integral electrode configuration. Here, recent advancements in the design and synthesis of wood-structured nanomaterials serving as advanced electrocatalysts for water splitting are summarized. First, the design principles and corresponding strategies toward highly effective wood-structured electrocatalysts (WSECs) are emphasized. Then, a comprehensive overview of current findings on WSECs, encompassing diverse structural designs and functionalities such as supported-metal nanoparticles (NPs), single-atom catalysts (SACs), metal compounds, and heterostructured electrocatalysts based on engineered wood hosts are presented. Subsequently, the application of these WSECs in various aspects of water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting (OWS), and hybrid water electrolysis (HWE) are explored. Finally, the prospects, challenges, and opportunities associated with the broad application of WSECs are briefly discussed. This review aims to provide a comprehensive understanding of the ongoing developments in water-splitting catalysts, along with outlining design principles for the future development of WSECs.

Ultrasonic-assisted Fenton reaction inducing surface reconstruction endows nickel/iron-layered double hydroxide with efficient water and organics electrooxidation

Nickel/iron-layered double hydroxide (NiFe-LDH) tends to undergo an electrochemically induced surface reconstruction during the water oxidation in alkaline, which will consume excess electric energy to overcome the reconstruction thermodynamic barrier. In the present work, a novel ultrasonic wave-assisted Fenton reaction strategy is employed to synthesize the surface reconstructed NiFe-LDH nanosheets cultivated directly on Ni foam (NiFe-LDH/NF-W). Morphological and structural characterizations reveal that the low-spin states of Ni2+ (t2g6eg2) and Fe2+ (t2g4eg2) on the NiFe-LDH surface partially transform into high-spin states of Ni3+ (t2g6eg1) and Fe3+ (t2g3eg2) and formation of the highly active species of NiFeOOH. A lower surface reconstruction thermodynamic barrier advantages the electrochemical process and enables the NiFe-LDH/NF-W electrode to exhibit superior electrocatalytic water oxidation activity, which delivers 10 mA cm-2 merely needing an overpotential of 235 mV. Besides, surface reconstruction endows NiFe-LDH/NF-W with outstanding electrooxidation activities for organic molecules of methanol, ethanol, glycerol, ethylene glycol, glucose, and urea. Ultrasonic-assisted Fenton reaction inducing surface reconstruction strategy will further advance the utilization of NiFe-LDH catalyst in water and organics electrooxidation.

Potential cycling boosts the electrochemical conversion of polyethylene terephthalate-derived alcohol into valuable chemicals

The electrocatalytic valorization of polyethylene terephthalate-derived ethylene glycol to valuable glycolic acid offers considerable economic and environmental benefits. However, conventional methods face scalability issues due to rapid activity decay of noble metal electrocatalysts. We demonstrate that a dynamic potential cycling approach, which alternates the electrode potential between oxidizing and reducing values, significantly mitigates surface deactivation of noble metals during electrochemical oxidation of ethylene glycol. This method enhances catalyst activity by 20 times compared to a constant-potential approach, maintaining this performance for up to 60 h with minimal deactivation. In situ Raman and X-ray absorption spectroscopy show that this effectiveness results from efficient removal of surface oxide during the reaction. The strategy is applicable to polyethylene terephthalate hydrolysates and various noble metals, such as palladium, gold, and platinum, with palladium showing a high conversion rate in recent studies. Our approach offers an efficient and durable method for electrochemical upcycling of biomass-derived compounds.

PET Glycolysis to BHET Efficiently Catalyzed by Stable and Recyclable Pd-Cu/γ-Al2O3

Glycolysis of poly(ethylene terephthalate) (PET) is a prospective way for degradation of PET to its monomer bis(hydroxyethyl) terephthalate (BHET), providing the possibility for a permanent loop recycling. However, most reported glycolysis catalysts are homogeneous, making the catalyst difficult to recover and contaminating the products. Herein, we reported on the Pd-Cu/γ-Al2O3 catalyst and applied it in the glycolysis of PET as catalyst. The formed structure gave Pd-Cu/γ-Al2O3 a high active surface area, which enabled these micro-particles to work more efficiently. The PET conversion and BHET yield reached 99% and 86%, respectively, in the presence of 5 wt% of Pd-Cu/γ-Al2O3 catalyst within 80 min at 160 °C. After the reaction, the catalyst can be quickly separated by filtration, so it can be easily reused without significant loss of reactivity at least five times. Therefore, the Pd-Cu/γ-Al2O3 catalyst may contribute to an economically and environmentally improved large-scale recycling of PET fiber waste.

Spent Lithium-Ion Batteries Derived Co3O4 for Electrocatalytic Polyethylene Terephthalate Plastic Recycling

Spent lithium-ion batteries (LIBs) are an essential secondary resource containing valuable metal elements. Transforming spent LIBs into efficient catalysts through a simple process presents a promising strategy to address both metal resource scarcity and clean energy challenges. Herein, a deep eutectic solvent-assisted synthesis of Co3O4 material from spent LIBs is proposed. The obtained Co3O4 material possesses efficient and stable electrocatalytic activity for converting raw polyethylene terephthalate (PET) bottles into high-purity formic acid and terephthalic acid products under ambient conditions. As expected, the Co3O4 catalyst exhibits a high FE of 92 % with a concentration of produced potassium formate of 23.6 mM under alkaline conditions. This study presents a waste-treating-waste strategy for the simultaneous recovery of spent LIBs and PET waste in a greener manner.

Interstitial Boron Atoms in Pd Aerogel Selectively Switch the Pathway for Glycolic Acid Synthesis from Waste Plastics

Electro-reforming of poly(ethylene terephthalate) (PET) into valuable chemicals is garnering significant attention as it opens a mild avenue for waste resource utilization. However, achieving high activity and selectivity for valuable C2 products during ethylene glycol (EG) oxidation in PET hydrolysate on Pd electrocatalysts remains challenging. The strong interaction between Pd and carbonyl (*CO) intermediates leads to undesirable over-oxidation and poisoning of Pd sites, which hinders the highly efficient C2 products production. Herein, a nonmetallic alloying strategy is employed to fabricate a Pd-boron alloy aerogel (PdB), wherein B atoms are induced to regulate the electron structure and surface oxophilicity. This approach allows a remarkable mass activity of 6.71 A mgPd -1, glycolic acid (GA) Faradaic efficiency (FE) of 93.8%, and stable 100 h cyclic electrolysis. In situ experiments and density functional theory calculations reveal the contributions of B inserted in Pd lattice on highly effective EG-to-GA conversion. Interestingly, the heightened surface oxophilicity and regulated electronic structure by B incorporation weakened *CO intermediates adsorption and enhanced hydroxyl species affinity to accelerate oxidative *OH adspecies formation, thereby synergistically avoiding over-oxidation and boosting GA synthesis. This work provides valuable insights for the rational design of high-performance electrocatalysts for GA synthesis via an oxophilic B motifs incorporation strategy.