Emerging Nanomaterials toward Uranium Extraction from Seawater: Recent Advances and Perspectives.

Nuclear energy holds great potential to facilitate the global energy transition and alleviate the increasing environmental issues due to its high energy density, stable energy output, and carbon-free emission merits. Despite being limited by the insufficient terrestrial uranium reserves, uranium extraction from seawater (UES) can offset the gap. However, the low uranium concentration, the complicated uranium speciation, the competitive metal ions, and the inevitable marine interference remarkably affect the kinetics, capacity, selectivity, and sustainability of UES materials. To date, massive efforts have been made with varying degrees of success to pursue a desirable UES performance on various nanomaterials. Nevertheless, comprehensive and systematic coverage and discussion on the emerging UES materials presenting the fast-growing progress of this field is still lacking. This review thus challenges this position and emphatically focuses on this topic covering the current mainstream UES technologies with the emerging UES materials. Specifically, this review elucidates the causality between the physiochemical properties of UES materials induced by the intellectual design strategies and the UES performances and further dissects the relationships of materials-properties-activities and the corresponding mechanisms in depth. This review is envisaged to inspire innovative ideas and bring technical solutions for developing technically and economically viable UES materials.

Tip-like Fe-N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction.

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip-like FeN4 sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN4 sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Surface Spin Enhanced High Stable NiCo2 S4 for Energy-Saving Production of H2 from Water/Methanol Coelectrolysis at High Current Density.

Nickel based materials are promising electrocatalysts to produce hydrogen from water in alkaline media. However, the stability is of great challenge, limiting its practical material functions. Herein, a new technique for electro-deposition flower-like NiCo2 S4 nanosheets on carbon-cloth (CC@NiCo2 S4 ) is proposed for energy-saving production of H2 from water/methanol coelectrolysis at high current density by constructing array architectures and regulating surface magnetism. The optimized and fine-tuned magnetism on the surface of the electrochemical in situ grown CC@NiCo2 S4 nanosheet array result in (0 1 -1) surface universally exposed, high catalytic activity for methanol electrooxidation, and long-term stability at high current density. X-ray photoelectron spectroscopy in combination of density functional theory calculations confirm the valence electron states and spin of d electrons for the surface of NiCo2 S4 , which enhance the surface stability of catalysts. This technology may be utilized to alter the surface magnetism and increase the stability of Ni-based electrocatalytic materials in general.

A Direct Formaldehyde Fuel Cell for CO2 -Emission Free Co-generation of Electrical Energy and Valuable Chemical/Hydrogen.

Converting carbon-based molecular fuels into electricity efficiently and cleanly without emitting CO2 remains a challenge. Conventional fuel cells using noble metals as anode catalysts often suffer performance degradation due to CO poisoning and a host of problems associated with CO2 production. This study provides a CO2 -emission-free direct formaldehyde fuel cell. It enables a flow of electricity while producing H2 and valuable formate. Unlike conventional carbon-based molecules electrooxidation, formaldehyde 1-electron oxidation is performed on the Cu anode with high selectivity, thus generating formate and H2 without undergoing CO2 pathway. In addition, the fuel cell produces 0.62 Nm3 H2 and 53 mol formate per 1 kWh of electricity generated, with an open circuit voltage of up to 1 V and a peak power density of 350 mW cm-2 . This study puts forward a zero-carbon solution for the efficient utilization of carbon-based molecule fuels that generates electricity, hydrogen and valuable chemicals in synchronization.

Oxygen Vacancy-Mediated Selective C-N Coupling toward Electrocatalytic Urea Synthesis.

The electrocatalytic C-N coupling for one-step urea synthesis under ambient conditions serves as the promising alternative to the traditional urea synthetic protocol. However, the hydrogenation of intermediate species hinders the efficient urea synthesis. Herein, the oxygen vacancy-enriched CeO2 was demonstrated as the efficient electrocatalyst with the stabilization of the crucial intermediate of *NO via inserting into vacant sites, which is conducive to the subsequent C-N coupling process rather than protonation, whereas the poor selectivity of C-N coupling with protonation was observed on the vacancy-deficient catalyst. The oxygen vacancy-mediated selective C-N coupling was distinguished and validated by the in situ sum frequency generation spectroscopy. The introduction of oxygen vacancies tailors the common catalyst carrier into an efficient electrocatalyst with a high urea yield rate of 943.6 mg h-1 g-1, superior than that of partial noble-metal-based electrocatalysts. This work provides novel insights into the catalyst design and developments of coupling systems.

Pt-Co Electrocatalysts: Syntheses, Morphologies, and Applications.

Pt-Co electrocatalysts have attracted significant attention because of their excellent performance in many electrochemical reactions. This review focuses on Pt-Co electrocatalysts designed and prepared for electrocatalytic applications. First, the various synthetic methods and synthesis mechanisms are systematically summarized; typical examples and core synthesis parameters are discussed for regulating the morphology and structure. Then, starting with the design and structure-activity relationship of catalysts, the research progress of the morphologies and structures of Pt-Co electrocatalysts obtained based on various strategies, the structure-activity relationship between them, and their properties are summarized. In addition, the important electrocatalytic applications and mechanisms of Pt-Co catalysts, including electrocatalytic oxidation/reduction and bifunctional catalytic reactions, are described and summarized, and their high catalytic activities are discussed on the basis of their mechanism and active sites. Moreover, the advanced electrochemical in situ characterization techniques are summarized, and the challenges and direction concerning the development of high-performance Pt-Co catalysts in electrocatalysis are discussed.

Unravelling the origin of long-term stability for Cs+ and Sr2+ solidification inside sodalite.

Cesium (Cs+) and strontium (Sr2+) ions are the main fission byproducts in the reprocessing of spent nuclear fuels for nuclear power plants. Their long half-live period (30.17 years for 137Cs and 28.80 years for 90Sr) makes them very dangerous radionuclides. Hence the solidification of Cs+ and Sr2+ is of paramount importance for preventing them from entering the human food chain through water. Despite tremendous efforts for solidification, the long-term stability remains a great challenge due to the experimental limitation and lack of good evaluation indicators for such long half-life radionuclides. Using density functional theory (DFT), we investigate the origin of long-term stability for the solidification of Cs+ and Sr2+ inside sodalite and establish that the exchange energy and the diffusion barrier play an important role in gaining the long-term stability both thermodynamically and kinetically. The acidity/basicity, solvation, temperature, and diffusion effect are comprehensively studied. It is found that solidification of Cs+ and Sr2+ is mainly attributed to the solvation effect, zeolitic adsorption ability, and diffusion barriers. The present study provides theoretical evidence to use geopolymers to adsorb Cs+ and Sr2+ and convert the adsorbed geopolymers to zeolites to achieve solidification of Cs+ and Sr2+ with long-term stability.

p-d Orbital Hybridization Induced by a Monodispersed Ga Site on a Pt3 Mn Nanocatalyst Boosts Ethanol Electrooxidation.

Constructing monodispersed metal sites in heterocatalysis is an efficient strategy to boost their catalytic performance. Herein, a new strategy using monodispersed metal sites to tailor Pt-based nanocatalysts is addressed by engineering unconventional p-d orbital hybridization. Thus, monodispersed Ga on Pt3 Mn nanocrystals (Ga-O-Pt3 Mn) with high-indexed facets was constructed for the first time to drive ethanol electrooxidation reaction (EOR). Strikingly, the Ga-O-Pt3 Mn nanocatalyst shows an enhanced EOR performance with achieving 8.41 times of specific activity than that of Pt/C. The electrochemical in situ Fourier transform infrared spectroscopy results and theoretical calculations disclose that the Ga-O-Pt3 Mn nanocatalyst featuring an unconventional p-d orbital hybridization not only promote the C-C bond-breaking and rapid oxidation of -OH of ethanol, but also inhibit the generation of poisonous CO intermediate species. This work discloses a promising strategy to construct a novel nanocatalysts tailored by monodispersed metal site as efficient fuel cell catalysts.

Transforming Electrocatalytic Biomass Upgrading and Hydrogen Production from Electricity Input to Electricity Output.

Integrating biomass upgrading and hydrogen production in an electrocatalytic system is attractive both environmentally and in terms of sustainability. Conventional electrolyser systems coupling anodic biosubstrate electrooxidation with hydrogen evolution reaction usually require electricity input. Herein, we describe the development of an electrocatalytic system for simultaneous biomass upgrading, hydrogen production, and electricity generation. In contrast to conventional furfural electrooxidation, the employed low-potential furfural oxidation enabled the hydrogen atom of the aldehyde group to be released as gaseous hydrogen at the anode at a low potential of approximately 0 VRHE (vs. RHE). The integrated electrocatalytic system could generate electricity of about 2 kWh per cubic meter of hydrogen produced. This study may provide a transformative technology to convert electrocatalytic biomass upgrading and hydrogen production from a process requiring electricity input into a process to generate electricity.

Understanding the Roles of Electrogenerated Co3+ and Co4+ in Selectivity-Tuned 5-Hydroxymethylfurfural Oxidation.

The Co-based electrocatalyst is among the most promising candidates for electrochemical oxidation of 5-hydroxymethylfurfural (HMF). However, the intrinsic active sites and detailed mechanism of this catalyst remains unclear. We combine experimental evidence and a theoretical study to show that electrogenerated Co3+ and Co4+ species act as chemical oxidants but with distinct roles in selective HMF oxidation. It is found that Co3+ is only capable of oxidizing formyl group to produce carboxylate while Co4+ is required for the initial oxidation of hydroxyl group with significantly faster kinetics. As a result, the product distribution shows explicit dependence on the Co oxidation states and selective production of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 2,5-furandicarboxylic acid (FDCA) are achieved by tuning the applied potential. This work offers essential mechanistic insight on Co-catalyzed organic oxidation reactions and might guide the design of more efficient electrocatalysts.

Metal-Tuned Acetylene Linkages in Hydrogen Substituted Graphdiyne Boosting the Electrochemical Oxygen Reduction.

Different from graphene with the highly stable sp2 -hybridized carbon atoms, which shows poor controllability for constructing strong interactions between graphene and guest metal, graphdiyne has a great potential to be engineered because its high-reactive acetylene linkages can effectively chelate metal atoms. Herein, a hydrogen-substituted graphdiyne (HsGDY) supported metal catalyst system through in situ growth of Cu3 Pd nanoalloys on HsGDY surface is developed. Benefiting from the strong metal-chelating ability of acetylenic linkages, Cu3 Pd nanoalloys are intimately anchored on HsGDY surface that accordingly creates a strong interaction. The optimal HsGDY-supported Cu3 Pd catalyst (HsGDY/Cu3 Pd-750) exhibits outstanding electrocatalytic activity for the oxygen reduction reaction (ORR) with an admirable half-wave potential (0.870 V), an impressive kinetic current density at 0.75 V (57.7 mA cm-2 ) and long-term stability, far outperforming those of the state-of-the-art Pt/C catalyst (0.859 V and 15.8 mA cm-2 ). This excellent performance is further highlighted by the Zn-air battery using HsGDY/Cu3 Pd-750 as cathode. Density function theory calculations show that such electrocatalytic performance is attributed to the strong interaction between Cu3 Pd and CC bonds of HsGDY, which causes the asymmetric electron distribution on two carbon atoms of CC bond and the strong charge transfer to weaken the shoulder-to-shoulder π conjugation, eventually facilitating the ORR process.

Interfacial Electronic Modulation of Dual-Monodispersed Pt-Ni3S2 as Efficacious Bi-Functional Electrocatalysts for Concurrent H2 Evolution and Methanol Selective Oxidation.

Constructing the efficacious and applicable bi-functional electrocatalysts and establishing out the mechanisms of organic electro-oxidation by replacing anodic oxygen evolution reaction (OER) are critical to the development of electrochemically-driven technologies for efficient hydrogen production and avoid CO2 emission. Herein, the hetero-nanocrystals between monodispersed Pt (~ 2 nm) and Ni3S2 (~ 9.6 nm) are constructed as active electrocatalysts through interfacial electronic modulation, which exhibit superior bi-functional activities for methanol selective oxidation and H2 generation. The experimental and theoretical studies reveal that the asymmetrical charge distribution at Pt-Ni3S2 could be modulated by the electronic interaction at the interface of dual-monodispersed heterojunctions, which thus promote the adsorption/desorption of the chemical intermediates at the interface. As a result, the selective conversion from CH3OH to formate is accomplished at very low potentials (1.45 V) to attain 100 mA cm-2 with high electronic utilization rate (~ 98%) and without CO2 emission. Meanwhile, the Pt-Ni3S2 can simultaneously exhibit a broad potential window with outstanding stability and large current densities for hydrogen evolution reaction (HER) at the cathode. Further, the excellent bi-functional performance is also indicated in the coupled methanol oxidation reaction (MOR)//HER reactor by only requiring a cell voltage of 1.60 V to achieve a current density of 50 mA cm-2 with good reusability.

Atomic Diffusion Engineered PtSnCu Nanoframes with High-Index Facets Boost Ethanol Oxidation.

Electrochemical ethanol oxidation is crucial to directly convert a biorenewable liquid fuel with high energy density into electrical energy, but it remains an inefficient reaction even with the best catalysts. To boost ethanol oxidation, developing multimetallic nanoalloy has emerged as one of the most effective strategies, yet faces a challenge in the rational engineering of multimetallic active-site ensembles at atomic-level. Herein, starting from typical PtCu nanocrystals, an atomic Sn diffusion strategy is developed to construct well-defined Pt47Sn12Cu41 octopod nanoframes, which is enclosed by high-index facets of n (111)-(111), such as {331} and {221}. Pt47Sn12Cu41 achieves a high mass activity of 3.10 A mg-1 Pt and promotes the C-C bond breaking and oxidation of poisonous CO intermediate, representing a state-of-the-art electrocatalyst toward ethanol oxidation in acidic electrolyte. Density functional theory （DFT） calculations have confirmed that the introduction of Sn improves the electroactivity by uplifting the d-band center through the s-p-d coupling. Meanwhile, the strong binding of ethanol and the reduced energy barrier of CO oxidation guarantee a highly efficient ethanol oxidation process with improved Faradic efficiency of C1 products. This work offers a promising strategy for constructing novel multimetallic nanoalloys tailored by atomic metal sites as the efficient electrocatalysts.

Visualizing Electrochemical CO2 Conversion via the Emerging Scanning Electrochemical Microscope: Fundamentals, Applications and Perspectives.

With the rapid development and maturity of electrochemical CO2 conversion involving cathodic CO2 reduction reaction (CO2RR) and anodic oxygen evolution reaction (OER), conventional ex situ characterizations gradually fall behind in detecting real-time products distribution, tracking intermediates, and monitoring structural evolution, etc. Nevertheless, advanced in situ techniques, with intriguing merits like good reproducibility, facile operability, high sensitivity, and short response time, can realize in situ detection and recording of dynamic data, and observe materials structural evolution in real time. As an emerging visual technique, scanning electrochemical microscope (SECM) presents local electrochemical signals on various materials surface through capturing micro-current caused by reactants oxidation and reduction. Importantly, SECM holds particular potentials in visualizing reactive intermediates at active sites and obtaining instantaneous morphology evolution images to reveal the intrinsic reactivity of active sites. Therefore, this review focuses on SECM fundamentals and its specific applications toward CO2RR and OER, mainly including electrochemical behavior observation on local regions of various materials, target products and onset potentials identification in real-time, reaction pathways clarification, reaction kinetics exploration under steady-state conditions, electroactive materials screening and multi-techniques coupling for a joint utilization. This review undoubtedly provides a leading guidance to extend various SECM applications to other energy-related fields.

Perovskite Oxides Toward Oxygen Evolution Reaction: Intellectual Design Strategies, Properties and Perspectives.

Developing electrochemical energy storage and conversion devices (e.g., water splitting, regenerative fuel cells and rechargeable metal-air batteries) driven by intermittent renewable energy sources holds a great potential to facilitate global energy transition and alleviate the associated environmental issues. However, the involved kinetically sluggish oxygen evolution reaction (OER) severely limits the entire reaction efficiency, thus designing high-performance materials toward efficient OER is of prime significance to remove this obstacle. Among various materials, cost-effective perovskite oxides have drawn particular attention due to their desirable catalytic activity, excellent stability and large reserves. To date, substantial efforts have been dedicated with varying degrees of success to promoting OER on perovskite oxides, which have generated multiple reviews from various perspectives, e.g., electronic structure modulation and heteroatom doping and various applications. Nonetheless, the reviews that comprehensively and systematically focus on the latest intellectual design strategies of perovskite oxides toward efficient OER are quite limited. To bridge the gap, this review thus emphatically concentrates on this very topic with broader coverages, more comparative discussions and deeper insights into the synthetic modulation, doping, surface engineering, structure mutation and hybrids. More specifically, this review elucidates, in details, the underlying causality between the being-tuned physiochemical properties [e.g., electronic structure, metal-oxygen (M-O) bonding configuration, adsorption capacity of oxygenated species and electrical conductivity] of the intellectually designed perovskite oxides and the resulting OER performances, coupled with perspectives and potential challenges on future research. It is our sincere hope for this review to provide the scientific community with more insights for developing advanced perovskite oxides with high OER catalytic efficiency and further stimulate more exciting applications.

Phase-Transition-Induced Surface Reconstruction of Rh1 Site in Intermetallic Alloy for Propane Dehydrogenation.

The fine-tuning of the geometric and electronic structures of active sites plays a crucial role in catalysis. However, the intricate entanglement between the two aspects results in a lack of interpretable design for active sites, posing a challenge in developing high-performance catalysts. Here, we find that surface reconstruction induced by phase transition in intermetallic alloys enables synergistic geometric and electronic structure modulation, creating a desired active site microenvironment for propane dehydrogenation. The resulting electron-rich four-coordinate Rh1 site in the RhGe0.5Ga0.5 intermetallic alloy can accelerate the desorption of propylene and suppress the side reaction and thus exhibits a propylene selectivity of ∼98% with a low deactivation constant of 0.002 h-1 under propane dehydrogenation at 550 °C. Furthermore, we design a computational workflow to validate the rationality of the microenvironment modulation induced by the phase transition in an intermetallic alloy.

Surface-Enriched Single-Bi-Atoms Tailoring of Pt Nanorings for Direct Methanol Fuel Cells with Ultralow-Pt-Loading.

Single-atom decorating of Pt emerges as a highly effective strategy to boost catalytic properties, which can trigger the most Pt active sites while blocking the smallest number of Pt atoms. However, the rational design and creation of high-density single-atoms on Pt surface remain as a huge challenge. Herein, a customized synthesis of surface-enriched single-Bi-atoms tailored Pt nanorings (SE-Bi1/Pt NRs) toward methanol oxidation is reported, which is guided by the density functional theory (DFT) calculations suggesting that a relatively higher density of Bi species on Pt surface can ensure a CO-free pathway and accelerate the kinetics of *HCOOH formation. Decorating Pt NRs with dense single-Bi-atoms is achieved by starting from PtBi intermetallic nanoplates (NPs) with intrinsically isolated Bi atoms and subsequent etching and annealing treatments. The SE-Bi1/Pt NRs exhibit a mass activity of 23.77 A mg-1 Pt toward methanol oxidation in alkaline electrolyte, which is 2.2 and 12.8 times higher than those of Pt-Bi NRs and Pt/C, respectively. This excellent activity endows the SE-Bi1/Pt NRs with a high likelihood to be used as a practical anodic electrocatalyst for direct methanol fuel cells （DMFCs） with high power density of 85.3 mW cm-2 and ultralow Pt loading of 0.39 mg cm-2.

N and S dual-coordinated Fe single-atoms in hierarchically porous hollow nanocarbon for efficient oxygen reduction.

Fe-, and N-co-doped carbon (FeNC) electrocatalysts are promising alternatives to Pt-based catalysts for oxygen reduction reaction (ORR); however, simultaneously enhancing their intrinsic activity and exposure of Fe active sites remains challenging. Herein, we report S-modified Fe single-atom catalysts (SACs) anchored on N,S-co-doped hollow porous nanocarbon (Fe/NS-C) for ORR. The unique hollow structure and large surface area of the SACs are favorable for mass/electron transport and exposure of Fe single-atom active sites. The as-prepared Fe/NS-C electrocatalysts display a high-efficiency ORR activity with a half-wave potential of 0.893 V versus the reversible hydrogen electrode and exceed that of the benchmark commercial Pt/C catalyst as well as most reported transition-metal based SACs. Impressively, the Fe/NS-C-based Al-air battery (AAB) displays a high open circuit voltage of 1.48 V, a maximum power density of 140.16 mW cm-2, and satisfactory durability, outperforming commercial Pt/C-based AAB. Furthermore, Fe/NS-C exhibits considerable potential as a cathode catalyst for application in direct methanol fuel cells. Experimental and theoretical calculation results reveal that the excellent ORR performance of Fe/NS-C can be contributed to the highly active FeN3S sites and the unique hollow structure. This work provides new insights into the rational design and synthesis high-performance ORR electrocatalysts for energy conversion and storage devices. of employing ZIF-8 as precursors.

Achieving Net-Zero Emissions with Solid Oxide Electrolysis Cells: The Power-to-X Approach.

Replacing fossil fuels with renewable energy sources is a crucial step for mitigating global warming. However, the intermittent nature of the most prevalent renewable sources, such as solar and wind, poses a significant challenge to their widespread deployment. One potential solution for renewable sources of storage is power-to-X, which involves the production of chemicals from electricity using solid oxide electrolysis cells. This process offers a flexible and efficient means of energy storage. This Perspective offers an overview of the characteristics, capabilities, and fundamental mechanisms of solid oxide electrolysis cells. It also examines the latest research progress and explores the prospects and challenges in this field.

Enhanced electrically and thermally conductive free-standing graphene films with two-dimensional copper sheets as the catalyst and bridge.

Two-dimensional copper sheets were introduced as the catalyst and bridge to enhance the electrical and thermal conductivity of graphene films prepared from graphene oxide nanosheets via a thermal reduction method. The effects of adding different amounts of copper sheets in the composite films were investigated, and the results show that the electrical and thermal conductivity of the graphene films could be increased by 3 times and 64.9%, respectively. The two-dimensional copper sheets not only play an important role as a catalyst toward improving the graphitization degree of reduced graphene oxide, but also act as a bridge and promote the interconnection of the electrical and thermal conduction paths in the composite films due to the good electrical and thermal conductivity of copper. Moreover, the heat dissipation experiment shows that this enhanced graphene composite film has potential applications in the heat management of electronics.