Upcycling of Spent LiFePO4 Cathodes to Heterostructured Electrocatalysts for Stable Direct Seawater Splitting.

The pursuit of carbon-neutral energy has intensified the interest in green hydrogen production from direct seawater electrolysis, given the scarcity of freshwater resources. While Ni-based catalysts are known for their robust activity in alkaline water oxidation, their catalytic sites are prone to rapid degradation in the chlorine-rich environments of seawater, leading to limited operation time. Herein, we report a Ni(OH)2 catalyst interfaced with laser-ablated LiFePO4 (Ni(OH)2/L-LFP), derived from spent Li-ion batteries (LIBs), as an effective and stable electrocatalyst for direct seawater oxidation. Our comprehensive analyses reveal that the PO43- species, formed around L-LFP, effectively repels Cl- ions during seawater oxidation, mitigating corrosion. Simultaneously, the interface between in situ generated NiOOH and Fe3(PO4)2 enhances OH- adsorption and electron transfer during the oxygen evolution reaction. This synergistic effect leads to a low overpotential of 237 mV to attain a current density of 10 mA cm-2 and remarkable durability, with only a 3.3 % activity loss after 600 h at 100 mA cm-2 in alkaline seawater. Our findings present a viable strategy for repurposing spent LIBs into high-performance catalysts for sustainable seawater electrolysis, contributing to the advancement of green hydrogen production technologies.

Photoreforming of Microplastics: Challenges and Opportunities for Sustainable Environmental Remediation.

Plastics are widely used in daily lives, but unfortunately, their inadequate recycling practices have led to the accumulation of microplastics in the environment, posing a threat to public health. The existing methods for treating microplastics are energy-intensive and environmentally damaging. In this context, photoreforming has emerged as a sustainable solution to address the microplastic crisis by simultaneously recycling them into value-added chemicals. This review presents a comprehensive overview of the application of photoreforming for upcycling microplastic. The underlying mechanisms of photoreforming reaction are discussed, followed by the exploration of recent advancements and innovative strategies in photoreforming techniques with particular emphasis on their real-world applications and potential for large-scale implementation. Also, critical factors influencing the efficiency of microplastic photoreforming are identified, providing guidance for further research and optimization.

Waste plastics upcycled for high-efficiency H2O2 production and lithium recovery via Ni-Co/carbon nanotubes composites.

The disposal and management of waste lithium-ion batteries (LIBs) and low-density polyethylene (LDPE) plastics pose significant environmental challenges. Here we show a synergistic pyrolysis approach that employs spent lithium transition metal oxides and waste LDPE plastics in one sealed reactor to achieve the separation of Li and transition metal. Additionally, we demonstrate the preparation of nanoscale NiCo alloy@carbon nanotubes (CNTs) through co-pyrolysis of LiNi0.6Co0.2Mn0.2O2 and LDPE. The NiCo alloy@CNTs exhibits excellent catalytic activity (Eonset = ~0.85 V) and the selectivity (~90%) for H2O2 production through the electrochemical reduction of oxygen. This can be attributed to the NiCo nanoalloy core and the presence of CNTs with abundant oxygen-containing functional groups (e.g., -COOH and C-O-C), as confirmed by density function theory calculations. Overall, this work presents a straightforward and green approach for valorizing and upcycling various waste LIBs and LDPE plastics.

Amphipathic Surfactant on Reconstructed Bismuth Enables Industrial-Level Electroreduction of CO2 to Formate.

Developing efficient electrocatalysts for selective formate production via the electrochemical CO2 reduction reaction (CO2RR) is challenged by high overpotential, a narrow potential window of high Faradaic efficiency (FEformate), and limited current density (Jformate). Herein, we report a hierarchical BiOBr (CT/h-BiOBr) with surface-anchored cetyltrimethylammonium bromide (CTAB) for formate-selective large-scale CO2RR electrocatalysis. CT/h-BiOBr achieves over 90% FEformate across a wide potential range (-0.5 to -1.1 V) and an industrial-level Jformate surpassing 100 mA·cm-2 at -0.7 V. In situ investigations uncover the reconstructed Bi(110) surface as the active phase, with CTAB playing a dual role: its hydrophobic alkyl chains create a CO2-enriching microenvironment, while its polar head groups fine-tune the electronic structure, fostering a highly active phase. This work provides valuable insights into the role of surfactants in electrocatalysis and guides the design of electrocatalysts for the large-scale CO2RR.

Spatial engineering of single-atom Fe adjacent to Cu-assisted nanozymes for biomimetic O2 activation.

The precise design of single-atom nanozymes (SAzymes) and understanding of their biocatalytic mechanisms hold great promise for developing ideal bio-enzyme substitutes. While considerable efforts have been directed towards mimicking partial bio-inspired structures, the integration of heterogeneous SAzymes configurations and homogeneous enzyme-like mechanism remains an enormous challenge. Here, we show a spatial engineering strategy to fabricate dual-sites SAzymes with atomic Fe active center and adjacent Cu sites. Compared to planar Fe-Cu dual-atomic sites, vertically stacked Fe-Cu geometry in FePc@2D-Cu-N-C possesses highly optimized scaffolds, favorable substrate affinity, and fast electron transfer. These characteristics of FePc@2D-Cu-N-C SAzyme induces biomimetic O2 activation through homogenous enzymatic pathway, resembling functional and mechanistic similarity to natural cytochrome c oxidase. Furthermore, it presents an appealing alternative of cytochrome P450 3A4 for drug metabolism and drug-drug interaction. These findings are expected to deepen the fundamental understanding of atomic-level design in next-generation bio-inspired nanozymes.

Surface-Reconstructed Ru-Doped Nickel/Iron Oxyhydroxide Arrays for Efficient Oxygen Evolution.

The generation of an active phase through dynamic surface reconstruction is a promising strategy for improving the activity of electrocatalysts. However, studies investigating the reconstruction process and its impact on the intrinsic properties of the catalysts are scarce. Herein, the surface reconstruction of NiFe2 O4 interfaced with NiMoO4 (Ru-NFO/NMO) facilitated by Ru doping is reported. The electrochemical and material characterizations demonstrate that Ru doping can regulate the electronic structure of NFO/NMO and induce the high-valence state of Ni3.6+ δ , facilitating the surface reconstruction to highly active Ru-doped NiFeOOH/NiOOH (SR-Ru-NFO/NMO). The optimized SR-Ru-NFO/NMO exhibits promising performance in the oxygen evolution reaction, displaying a low overpotential of 229 mV at 10 mA cm-2 and good stability at varying current densities for 80 h. Density functional theory calculations indicate that Ru doping can increase the electron density and optimize intermediate adsorption by shifting the d-band center downward. This work provides valuable insights into the tuning of electrocatalysts by surface reconstruction and offers a rational design strategy for the development of highly active oxygen evolution reaction electrocatalysts.

An emerging direction for nanozyme design: from single-atom to dual-atomic-site catalysts.

Nanozymes, a new class of functional nanomaterials with enzyme-like characteristics, have recently made great achievements and have become potential substitutes for natural enzymes. In particular, single-atomic nanozymes (Sazymes) have received intense research focus on account of their versatile enzyme-like performances and well-defined spatial configurations of single-atomic sites. More recently, dual-atomic-site catalysts (DACs) containing two neighboring single-atomic sites have been explored as next-generation nanozymes, thanks to the flexibility in tuning active sites by various combinations of two single-atomic sites. This minireview outlines the research progress of DACs in their synthetic approaches and the latest characterization techniques highlighting a series of representative examples of DAC-based nanozymes. In the final remarks, we provide current challenges and perspectives for developing DAC-based nanozymes as a guide for researchers who would be interested in this exciting field.

Recycling Spent Lithium-Ion Batteries Using Waste Benzene-Containing Plastics: Synergetic Thermal Reduction and Benzene Decomposition.

Spent lithium-ion batteries (LIBs) and benzene-containing polymers (BCPs) are two major pollutants that cause serious environmental burdens. Herein, spent LIBs and BCPs are copyrolyzed in a sealed reactor to generate Li2CO3, metals, and/or metal oxides without emitting toxic benzene-based gases. The use of a closed reactor allows the sufficient reduction reaction between the BCP-derived polycyclic aromatic hydrocarbon (PAH) gases and lithium transition metal oxides, achieving the Li recovery efficiencies of 98.3, 99.9, and 97.5% for LiCoO2, LiMn2O4, and LiNi0.6Co0.2Mn0.2O2, respectively. More importantly, the thermal decomposition of PAHs (e.g., phenol and benzene) is further catalyzed by the in situ generated Co, Ni, and MnO2 particles, which forms metal/carbon composites and thus prevent the emissions of toxic gases. Overall, the copyrolysis in a closed system paves a green way to synergistically recycle spent LIBs and handle waste BCPs.

Highly Stable Sb/C Anode for K+ and Na+ Energy Storage Enabled by Pulsed Laser Ablation and Polydopamine Coating.

Potassium- and sodium-ion batteries (PIBs and SIBs) have great potential as the next-generation energy application owing to the natural abundance of K and Na. Antimony (Sb) is a suitable alloying-type anode for PIBs and SIBs due to its high theoretical capacity and proper operation voltage; yet, the severe volume variation remains a challenge. Herein, a preparation of N-doped carbon-wrapped Sb nanoparticles (L-Sb/NC) using pulsed laser ablation and polydopamine coating techniques, is reported. As the anode for PIB and SIB, the L-Sb/NC delivers superior rate capabilities and excellent cycle stabilities (442.2 and 390.5 mA h g-1 after 250 cycles with the capacity decay of 0.037% and 0.038% per cycle) at the current densities of 0.5 and 1.0 A g-1 , respectively. Operando X-ray diffraction reveals the facilitated and stable potassiation and sodiation mechanisms of L-Sb/NC enabled by its optimal core-shell structure. Furthermore, the SIB full cell fabricated with L-Sb/NC and Na3 V2 (PO4 )2 F3 shows outstanding electrochemical performances, demonstrating its practical energy storage application.

Rational design and structural engineering of heterogeneous single-atom nanozyme for biosensing.

Nanozymes, an emerging family of heterogeneous nanomaterials with enzyme-like characteristics, offer significant advantages as alternatives to natural enzymes for diverse biocatalytic applications. Nevertheless, the inhomogeneous configuration of nanomaterials makes it extremely challenging to develop nanozymes of desired performance and reaction mechanism. Single-atom nanozymes (SAzymes) that are composed of single-atomic active sites may provide an answer to these challenges with remarkable enzyme-like activity and specificity. The well-defined coordination microenvironments of SAzymes offer a suitable model system to investigate the structure-activity relationship and thus bridge the gap between natural enzyme and nanozyme. In this review, we would first present an overview of discoveries, advantages, and classifications of SAzymes. Then, we would discuss the reaction mechanism, design principles, and biosensing applications of a series of typical SAzymes with a focus on the rational design strategies for targeted reaction and the effort to uncover the catalytic mechanism at the atomic scale. Finally, we would provide the challenges and future perspectives of SAzymes as the next-generation nanozymes.

Tuning the Site-to-Site Interaction in Ru-M (M = Co, Fe, Ni) Diatomic Electrocatalysts to Climb up the Volcano Plot of Oxygen Electroreduction.

The modulating of the geometric and electronic structures of metal-N-C atomic catalysts for improving their performance in catalyzing oxygen reduction reactions (ORRs) is highly desirable yet challenging. We herein report a delicate "encapsulation-substitution" strategy for the synthesis of paired metal sites in N-doped carbon. With the regulation of the d-orbital energy level, a significant increment in oxygen electroreduction activity was demonstrated in Ru-Co diatomic catalyst (DAC) compared with other diatomic (Ru-Fe and Ru-Ni) and single-atomic counterparts. The Ru-Co DAC efficiently reduces oxygen with a halfwave potential of 0.895 V vs RHE and a turnover frequency of 2.424 s-1 at 0.7 V, establishing optimal thermodynamic and kinetic behaviors in the triple-phase reaction under practical conditions. Moreover, the Ru-Co DAC electrode displays bifunctional activity in a gas diffusion Zn-air battery with a small voltage gap of 0.603 V, outperforming the commercial Pt/C|RuO2 catalyst. Our findings provide a clear understanding of site-to-site interaction on ORR and a benchmark evaluation of atomic catalysts with correlations of diatomic structure, energy level, and overall catalytic performance at the subnanometer level.

Observing Electrocatalytic Processes via In Situ Electrochemical Scanning Tunneling Microscopy: Latest Advances.

Electrocatalysis is the foundation of many techniques currently used to address environmental and energy problems. Therefore, understanding the electrocatalytic processes is essential to guide the rational design of electrocatalysts. Scanning tunneling microscopy (STM), developed in the 1980s, remains one of the few techniques that allow surface imaging at the atomic level, making it incredibly useful in electrocatalytic research. In this review, we introduced the basic concept and latest applications of the STM technique for in situ studies of electrocatalytic processes, particularly its capability in active site identification, species adsorption/desorption analysis, surface reconstruction imaging, and electrocatalyst dissolution detection, as well as its advantages and limitations.

Laser-Ablated Red Phosphorus on Carbon Nanotube Film for Accelerating Polysulfide Conversion toward High-Performance and Flexible Lithium-Sulfur Batteries.

The use of a conducting interlayer between separator and cathode is one of the most promising methods to trap lithium polysulfides (LiPSs) for enhancing the performance of lithium-sulfur (Li-S) batteries. Red phosphorus nanoparticles (RPEN )-coated carbon nanotube (CNT) film (RPEN @CF) is reported herein as a novel interlayer for Li-S batteries, which shows strong chemisorption of LiPSs, good flexibility, and excellent electric conductivity. A pulsed laser ablation method is engaged for the ultrafast production of RPEN of uniform morphology, which are deposited on the CNT film by a direct spinning method. The RPEN @CF interlayer provides pathways for effective Li+ and electron transfer and strong chemical interaction with LiPSs. The S/RPEN @CF electrode shows a superior specific capacity of 782.3 mAh g-1 (3 C-rate) and good cycling performances (769.5 mAh g-1 after 500 cycles at 1 C-rate). Density functional theory calculations reveal that the morphology and dispersibility of RPEN are crucial in enhancing Li+ and electron transfer kinetics and effective trap of LiPSs. This work demonstrates the possibility of using the RPEN @CF interlayer for the enhanced electrochemical performances of Li-S batteries and other flexible energy storage devices.

Synergies of Fe Single Atoms and Clusters on N-Doped Carbon Electrocatalyst for pH-Universal Oxygen Reduction.

Single atomic metal-N-C materials have attracted immense interest as promising candidates to replace noble metal-based electrocatalysts for the oxygen reduction reaction (ORR). The coordination environment of metal-N-C active centers plays a critical role in determining their catalytic activity and durability, however, attention is focused only on the coordination of metal atoms. Herein, Fe single atoms and clusters co-embedded in N-doped carbon (Fe/NC) that deliver the synergistic enhancement in pH-universal ORR catalysis via the four-electron pathway are reported. Combining a series of experimental and computational analyses, the geometric and electronic structures of catalytic sites in Fe/NC are revealed and the neighboring Fe clusters are shown to weaken the binding energies of the ORR intermediates on Fe-N sites, hence enhancing both catalytic kinetics and thermodynamics. This strategy provides new insights into the understanding of the mechanism of single atom catalysis.

Improving the performance stability of direct seawater electrolysis: from catalyst design to electrode engineering.

Direct seawater electrolysis opens a new opportunity to lower the cost of hydrogen production from current water electrolysis technologies. To facilitate its commercialization, the challenges of long-term performance stability of electrochemical devices need to be first addressed and realized. This minireview summarised the common causes of performance decline during seawater electrolysis, from chemical reactions at the electrode surface to physical damage to the cell. The problems triggered by the impurities in seawater are specifically discussed. Following these issues, we further outlined the ongoing effort of counter-measurements: from electrocatalyst optimization to electrode engineering and cell design. The recent progress in selectivity tuning, surface protection, gas diffusion, and cell configuration is highlighted. In the final remark, we emphasized the need for a consensus on evaluating the stability of seawater electrolysis in the current literature.

Interface Engineering of a 2D-C3N4/NiFe-LDH Heterostructure for Highly Efficient Photocatalytic Hydrogen Evolution.

Photocatalytic water splitting offers an economic and sustainable pathway for producing hydrogen as a zero-emission fuel, but it still suffers from low efficiencies limited by visible-light absorption capacity and charge separation kinetics. Herein, we report an interface-engineered 2D-C3N4/NiFe layered double hydroxide (CN/LDH) heterostructure that shows highly enhanced photocatalytic hydrogen evolution reaction (HER) rate with excellent long-term stability. The morphology and band gap structure of NiFe-LDH are precisely regulated by employing NH4F as a structure-directing agent, which enables a fine interfacial tuning via coupling with 2D-C3N4. The formation of a type II interface in CN/LDH enlarges the active surface area and promotes the charge separation efficiency, leading to an HER rate of 3087 µmol g-1 h-1, which is 14 times higher than that of 2D-C3N4. This study highlights a rational interface engineering strategy for the formation of a heterostructure with a proper hole transport co-catalyst for designing effective water-splitting photocatalysts.

Few-Layer Tellurium: Cathodic Exfoliation and Doping for Collaborative Hydrogen Evolution.

2D tellurium is a suitable electrocatalyst support that can assist electron transport while hosting active sites, yet its production remains challenging. Herein, a cathodic exfoliation method that can exfoliate Te crystal directly to Te nanosheets at low potential, also enabling simultaneous transition metal doping on Te nanosheet surface is presented. In situ Raman spectra and ex situ characterizations reveal that the cathodic exfoliation relies on the electrostatic repulsion between Te flakes covered with in situ generated ditelluride (Te2 2- ) anions. The Te2 2- anions can anchor metal ions to the surface, and the doping concentration can be tuned by adjusting the concentration of metal ion in the electrolyte. The metal-doped Te nanosheets exhibit highly improved hydrogen evolution activities. In particular, Pt-doped Te outperforms polycrystalline Pt at high overpotential. A collaborative hydrogen production mechanism via Volmer-Heyrovsky pathway is suggested: Te2 2- adsorbs protons and assists the mass transfer to adjacent Pt atoms where the protons are reduced and released as hydrogen.

Photocatalytic CO2 Reduction Enabled by Interfacial S-Scheme Heterojunction between Ultrasmall Copper Phosphosulfide and g-C3N4.

Transition metal phosphosulfides (TMPSs) have gained much interest due to their highly enhanced photocatalytic activities compared to their corresponding phosphides and sulfides. However, the application of TMPSs on photocatalytic CO2 reduction remains a challenge due to their inappropriate band positions and rapid recombination of photogenerated electron-hole pairs. Herein, we report ultrasmall copper phosphosulfide (us-Cu3P|S) nanocrystals anchored on 2D g-C3N4 nanosheets. Systematic studies on the interaction between us-Cu3P|S and g-C3N4 indicate the formation of an S-scheme heterojunction via interfacial P-N chemical bonds, which acts as an electron transfer channel and facilitates the separation and migration of photogenerated charge carriers. Upon the composite formation, the band structures of us-Cu3P|S and g-C3N4 are altered to enable the enhanced photocatalytic CO generation rate of 137 µmol g-1 h-1, which is eight times higher than that of pristine g-C3N4. The unique phosphosulfide structure is also beneficial for the enhanced electron transfer rate and provides abundant active sites. This first application of Cu3P|S to photocatalytic CO2 reduction marks an important step toward the development of TMPSs for photocatalytic applications.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Surface Engineering of MoS2 via Laser-Induced Exfoliation in Protic Solvents.

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS2 ) is considered a promising nonprecious candidate to substitute Pt-based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one-step exfoliation of bulk 2H-MoS2 to ultrastable few-layer MoS2 nanosheets. Such prepared MoS2 nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H-to-1T phase transition under laser irradiation. MoS2 exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm-2 and Tafel slope of 54 mV dec-1 .