Surface Reconstruction of La2CuO4 during the Electrochemical Reduction of Carbon Dioxide to Ethylene and Its Benefits for Enhanced Performance.

Electrochemical reduction (ECR) of CO2 to C2H4 has a potential key role in realizing the carbon neutral future, which ultimately relies on the availability of an efficient electrocatalyst that can exhibit a high Faradaic efficiency (FE) for C2H4 production and robust, long-term operational stability. Here, for the first time, we report that upon applying reductive potential and electrolyte to the benchmark La2CuO4 catalyst, surface reconstruction occurred, i.e., the appearance of a distinctive phase evolution process over time, which was successfully monitored using ex situ powder XRD and operando Mott-Schottky (M-S) measurements of La2CuO4 samples that were soaked into the electrolyte and subjected to CO2-ECR for different durations. At the end of such a reconstruction process, an outermost layer consisting of lanthanum carbonate, a thin outer layer made of an amorphous Cu+ material formed over the core bulk La2CuO4, as confirmed by various characterization techniques, which resulted in the redistribution of interfacial electrons and subsequent formation of electron-rich and electron-deficient interfaces. This contributed to the enhancement in FE for C2H4, reaching as much as 58.7%. Such surface reconstruction-induced electronic structure tuning gives new explanations for the superior catalytic performance of La2CuO4 perovskite and also provides a new pathway to advance CO2-ECR technology.

Advanced membrane-based electrode engineering toward efficient and durable water electrolysis and cost-effective seawater electrolysis in membrane electrolyzers.

Researchers have been seeking for the most technically-economical water electrolysis technology for entering the next-stage of industrial amplification for large-scale green hydrogen production. Various membrane-based electrolyzers have been developed to improve electric-efficiency, reduce the use of precious metals, enhance stability, and possibly realize direct seawater electrolysis. While electrode engineering is the key to approaching these goals by bridging the gap between catalysts design and electrolyzers development, nevertheless, as an emerging field, has not yet been systematically analyzed. Herein, this review is organized to comprehensively discuss the recent progresses of electrode engineering that have been made toward advanced membrane-based electrolyzers. For the commercialized or near-commercialized membrane electrolyzer technologies, the electrode material design principles are interpreted and the interface engineering that have been put forward to improve catalytic sites utilization and reduce precious metal loading is summarized. Given the pressing issues of electrolyzer cost reduction and efficiency improvement, the electrode structure engineering toward applying precious metal free electrocatalysts is highlighted and sufficient accessible sites within the thick catalyst layers with rational electrode architectures and effective ions/mass transport interfaces are enabled. In addition, this review also discusses the innovative ways as proposed to break the barriers of current membrane electrolyzers, including the adjustments of electrode reaction environment, and the feasible cell-voltage-breakdown strategies for durable direct seawater electrolysis. Hopefully, this review may provide insightful information of membrane-based electrode engineering and inspire the future development of advanced membrane electrolyzer technologies for cost-effective green hydrogen production.

Crystal structure optimization of copper oxides for the benzyl alcohol oxidation reaction.

In this work, experimental and theoretical analyses reveal that different types of Cu wires significantly change the adsorption properties of reactant molecules and the benzyl alcohol oxidation reaction performance. In particular, CuO nanowires in situ grown on Cu foam exhibit the best performance with a low potential of 1.39 V at a current density of 200 mA cm-2, high selectivity to benzoic acid production, and good operational stability.

Synergistic Bulk and Surface Engineering for Expeditious and Durable Reversible Protonic Ceramic Electrochemical Cells Air Electrode.

Reversible protonic ceramic electrochemical cells (R-PCECs) offer the potential for high-efficiency power generation and green hydrogen production at intermediate temperatures. However, the commercial viability of R-PCECs is hampered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) within conventional air electrodes operating at reduced temperatures. To address this challenge, this work introduces a novel approach based on the simultaneous optimization of bulk-phase metal-oxygen bonds and in-situ formation of a metal oxide nano-catalyst surface modification. This strategy is designed to expedite the ORR/OER electrocatalytic activity of air electrodes exhibiting triple (O2-, H+, e-) conductivity. Specifically, this engineered air electrode nanocomposite-Ba(Co0.4Fe0.4Zr0.1Y0.1)0.95Ni0.05F0.1O2.9-δ demonstrates remarkable ORR/OER catalytic activity and exceptional durability in R-PCECs. This is evidenced by significantly improved peak power density from 626 to 996 mW cm-2 and highly stable reversibility over a 100-h cycling period. This research offers a rational design strategy to achieve high-performance R-PCEC air electrodes with superior operational activity and stability for efficient and sustainable energy conversion and storage.

Development of Nanostructured Lanthanum Strontium Cobalt Ferrite/Gadolinian-Doped Ceria Composite Electrodes of Solid Oxide Cells Formed by In Situ Polarization.

In the development of nanoscale oxygen electrodes of high-temperature solid oxide cells (SOCs), the interface formed between the nanoelectrode particles and the electrolyte or electrolyte scaffolds is the most critical. In this work, a new synthesis technique for the fabrication of nanostructured electrodes via in situ electrochemical polarization treatment is reported. The lanthanum strontium cobalt ferrite (LSCF) precursor solution is infiltrated into a gadolinia-doped ceria (GDC) scaffold presintered on a yttria-stabilized zirconia (YSZ) electrolyte, followed by in situ polarization current treatment at SOC operation temperatures. Electrode ohmic and polarization resistances decrease with an increase in the polarization current treatment. Detailed microstructure analysis indicates the formation of a convex-shaped interface between the LSCF nanoparticles (NPs) and the GDC scaffold, very different from the flat contact between LSCF and GDC observed after heating at 800 °C with no polarization current treatment. The embedded LSCF NPs on the GDC scaffold contribute to the superior stability under both fuel cell and electrolysis operation conditions at 750 °C and a high peak power density of 1.58 W cm-2 at 750 °C. This work highlights a novel and facile route to in situ construct a stable and high-performing nanostructured electrode for SOCs.

Perovskite for Electrocatalytic Oxygen Evolution at Elevated Temperatures.

The development of advanced electrolysis technologies such as anion exchange membrane water electrolyzer (AEMWE) is central to the vision of a sustainable energy future. Key to the realization of such AEMWE technology lies in the exploration of low-cost and high-efficient catalysts for facilitating the anodic oxygen evolution reaction (OER). Despite tremendous efforts in the fundamental research, most of today's OER works are conducted under room temperature, which deviates significantly with AEMWE's operating temperature (50-80 °C). To bridge this gap, it is highly desirable to obtain insights into the OER catalytic behavior at elevated temperatures. Herein, using the well-known perovskite catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a proof of concept, the effect of temperature on the variation in OER catalytic activity and stability is evaluated. It is found that the BSCF's activity increases with increasing temperature due to enhanced lattice oxygen participation promoting the lattice oxygen-mediated OER process. Further, surface amorphization and cation leaching of BSCF become more pronounced as temperature increases, causing a somewhat attenuated OER stability. These new understandings of the fundamental OER catalysis over perovskite materials at industrial-relevant temperature conditions are expected to have strong implications for the research of OER catalysts to be deployed in practical water electrolyzers.

Engineering advanced noble-metal-free electrocatalysts for energy-saving hydrogen production from alkaline water via urea electrolysis.

When the anodic oxygen evolution reaction (OER) of water splitting is replaced by the urea oxidation reaction (UOR), the electrolyzer can fulfill hydrogen generation in an energy-economic manner for urea electrolysis as well as sewage purification. However, owing to the sluggish kinetics from a six-electron process for UOR, it is in great demand to design and fabricate high-performance and affordable electrocatalysts. Over the past years, numerous non-precious materials (especially nickel-involved samples) have offered huge potential as catalysts for urea electrolysis under alkaline conditions, even in comparison with frequently used noble-metal ones. In this review, recent efforts and progress in these high-efficiency noble-metal-free electrocatalysts are comprehensively summarized. The fundamentals and principles of UOR are first described, followed by highlighting UOR mechanism progress, and then some discussion about density functional theory (DFT) calculations and operando investigations is given to disclose the real reaction mechanism. Afterward, aiming to improve or optimize UOR electrocatalytic properties, various noble-metal-free catalytic materials are introduced in detail and classified into different classes, highlighting the underlying activity-structure relationships. Furthermore, new design trends are also discussed, including targetedly designing nanostructured materials, manipulating anodic products, combining theory and in situ experiments, and constructing bifunctional catalysts. Ultimately, we point out the outlook and explore the possible future opportunities by analyzing the remaining challenges in this booming field.

Advancing Catalysts by Stacking Fault Defects for Enhanced Hydrogen Production: A Review.

Green hydrogen, derived from water splitting powered by renewable energy such as solar and wind energy, provides a zero-emission solution crucial for revolutionizing hydrogen production and decarbonizing industries. Catalysts, particularly those utilizing defect engineering involving the strategical introduction of atomic-level imperfections, play a vital role in reducing energy requirements and enabling a more sustainable transition toward a hydrogen-based economy. Stacking fault (SF) defects play an important role in enhancing the electrocatalytic processes by reshaping surface reactivity, increasing active sites, improving reactants/product diffusion, and regulating electronic structure due to their dense generation ability and profound impact on catalyst properties. This review explores SF in metal-based materials, covering synthetic methods for the intentional introduction of SF and their applications in hydrogen production, including oxygen evolution reaction, photo- and electrocatalytic hydrogen evolution reaction, overall water splitting, and various other electrocatalytic processes such as oxygen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. Finally, this review addresses the challenges associated with SF-based catalysts, emphasizing the importance of a detailed understanding of the properties of SF-based catalysts to optimize their electrocatalytic performance. It provides a comprehensive overview of their various applications in electrocatalytic processes, providing valuable insights for advancing sustainable energy technologies.

Enhanced High-Temperature Cycling Stability of Garnet-Based All Solid-State Lithium Battery Using a Multi-Functional Catholyte Buffer Layer.

The pursuit of safer and high-performance lithium-ion batteries (LIBs) has triggered extensive research activities on solid-state batteries, while challenges related to the unstable electrode-electrolyte interface hinder their practical implementation. Polymer has been used extensively to improve the cathode-electrolyte interface in garnet-based all-solid-state LIBs (ASSLBs), while it introduces new concerns about thermal stability. In this study, we propose the incorporation of a multi-functional flame-retardant triphenyl phosphate additive into poly(ethylene oxide), acting as a thin buffer layer between LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and garnet electrolyte. Through electrochemical stability tests, cycling performance evaluations, interfacial thermal stability analysis and flammability tests, improved thermal stability (capacity retention of 98.5% after 100 cycles at 60 °C, and 89.6% after 50 cycles at 80 °C) and safety characteristics (safe and stable cycling up to 100 °C) are demonstrated. Based on various materials characterizations, the mechanism for the improved thermal stability of the interface is proposed. The results highlight the potential of multi-functional flame-retardant additives to address the challenges associated with the electrode-electrolyte interface in ASSLBs at high temperature. Efficient thermal modification in ASSLBs operating at elevated temperatures is also essential for enabling large-scale energy storage with safety being the primary concern.

Synergistic dual-phase air electrode enables high and durable performance of reversible proton ceramic electrochemical cells.

Reversible proton ceramic electrochemical cells are promising solid-state ion devices for efficient power generation and energy storage, but necessitate effective air electrodes to accelerate the commercial application. Here, we construct a triple-conducting hybrid electrode through a stoichiometry tuning strategy, composed of a cubic phase Ba0.5Sr0.5Co0.8Fe0.2O3-δ and a hexagonal phase Ba4Sr4(Co0.8Fe0.2)4O16-δ. Unlike the common method of creating self-assembled hybrids by breaking through material tolerance limits, the strategy of adjusting the stoichiometric ratio of the A-site/B-site not only achieves strong interactions between hybrid phases, but also can efficiently modifies the phase contents. When operate as an air electrode for reversible proton ceramic electrochemical cell, the hybrid electrode with unique dual-phase synergy shows excellent electrochemical performance with a current density of 3.73 A cm-2 @ 1.3 V in electrolysis mode and a peak power density of 1.99 W cm-2 in fuel cell mode at 650 °C.

Hydration deactivation mechanism of the 〈100〉 oriented cuprous oxide photocathodes in solar water splitting and the regenerated three-dimensional structure.

Photocorrosion is the most ticklish problem of cuprous oxide (Cu2O), and it is widely assumed that the deactivation of Cu2O photocathodes in solar water splitting is caused by spontaneous oxidation-reduction (REDOX) reactions. However, this work shows that 〈100〉-oriented Cu2O photocathodes undergo a non-REDOX hydration deactivation mechanism. Briefly, water molecules are embedded in the Cu2O crystals at low potential under illumination and produce amorphous CuOH, which can be dehydrated at high potential to heal the Cu-O-Cu bonds and regenerate foamed Cu2O films with a three-dimensional skeleton structure. This study provides a new insight towards the protection and application of Cu2O photocathodes.

Flexible silicon solar cells with high power-to-weight ratios.

Silicon solar cells are a mainstay of commercialized photovoltaics, and further improving the power conversion efficiency of large-area and flexible cells remains an important research objective1,2. Here we report a combined approach to improving the power conversion efficiency of silicon heterojunction solar cells, while at the same time rendering them flexible. We use low-damage continuous-plasma chemical vapour deposition to prevent epitaxy, self-restoring nanocrystalline sowing and vertical growth to develop doped contacts, and contact-free laser transfer printing to deposit low-shading grid lines. High-performance cells of various thicknesses (55-130 µm) are fabricated, with certified efficiencies of 26.06% (57 µm), 26.19% (74 µm), 26.50% (84 µm), 26.56% (106 µm) and 26.81% (125 µm). The wafer thinning not only lowers the weight and cost, but also facilitates the charge migration and separation. It is found that the 57-µm flexible and thin solar cell shows the highest power-to-weight ratio (1.9 W g-1) and open-circuit voltage (761 mV) compared to the thick ones. All of the solar cells characterized have an area of 274.4 cm2, and the cell components ensure reliability in potential-induced degradation and light-induced degradation ageing tests. This technological progress provides a practical basis for the commercialization of flexible, lightweight, low-cost and highly efficient solar cells, and the ability to bend or roll up crystalline silicon solar cells for travel is anticipated.

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells.

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

Nanotechnologies in ceramic electrochemical cells.

Although they are emerging technologies for achieving high-efficiency and green and eco-friendly energy conversion, ceramic electrochemical cells (CECs), i.e. solid oxide electrolysis cells (SOECs) and fuel cells (SOFCs), are still fundamentally limited by their inferior catalytic activities at low temperature, poor thermo-mechanical stability, high material cost, etc. The materials used in electrolytes and electrodes, which are the most important components in CECs, are highly associated with the cell performances. Therefore, rational design of electrolytes and electrodes with excellent catalytic activities and high stabilities at relatively low cost is a meaningful and valuable approach for the development of CECs. Nanotechnology is a powerful tool for improving the material performances in CECs owing to the favourable effects induced by the nanocrystallization of electrolytes and electrodes. Herein, a relatively comprehensive review on the nanotechnologies implemented in CECs is conducted. The working principles of CECs and the corresponding challenges were first presented, followed by the comprehensive insights into the working mechanisms of nanocrystalline materials in CECs. Then, systematic summarization and analyses of the commonly used nano-engineering strategies in the fabrication of CEC materials, including physical and chemical methods, were provided. In addition, the frontiers in the research of advanced electrolyte and electrode materials were discussed with a special emphasis on the modified electrochemical properties derived from nanotechnologies. Finally, the bottlenecks and the promising breakthroughs in nanotechnologies were highlighted in the direction of providing useful references for rational design of nanomaterials for CECs.

Plastic wastes-derived N-doped carbon nanotubes for efficient removal of sulfamethoxazole in high salinity wastewater via nonradical peroxymonosulfate activation.

Peroxymonosulfate (PMS) catalytic activation is effective to eliminate organic pollutants from water, thus the development of low-cost and efficient catalysts is significant in applications. The resource conversion of plastic wastes (PWs) into carbon nanotubes (CNTs) is a promising candidate for PMS-based advanced oxidation processes (AOPs), and also a sustainable strategy to realize plastic management and reutilization. Herein, cost-effective PWs-derived N-doped CNTs (N-pCNTs) were synthesized, which displayed efficient activity for PMS activation through an electron transfer pathway (ETP) for sulfamethoxazole (SMX) degradation in high salinity water. The pyrrolic N induced the positively charged surface of N-pCNTs, favoring the electrostatic adsorption of PMS and subsequent generation of active PMS* . A galvanic oxidation process was developed to prove the electron-shuttle dominated ETP for SMX oxidation. Combined with theoretical calculations, the efficiency of ETP was determined by the potential difference between HOMO of SMX and LUMO of N-pCNTs. Such oxidation produced low-toxicity intermediates and resulted in selective degradation of specific sulfonamide antibiotics. This work reveals the feasibility of low-cost N-pCNTs catalysts from PWs serving as an appealing candidate for PMS-AOPs in water remediation, providing a new solution to alleviate environmental issues caused by PWs and also advances the understanding of ETP during PMS activation.

Sintering-induced cation displacement in protonic ceramics and way for its suppression.

Protonic ceramic fuel cells with high efficiency and low emissions exhibit high potential as next-generation sustainable energy systems. However, the practical proton conductivity of protonic ceramic electrolytes is still not satisfied due to poor membrane sintering. Here, we show that the dynamic displacement of Y3+ adversely affects the high-temperature membrane sintering of the benchmark protonic electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, reducing its conductivity and stability. By introducing a molten salt approach, pre-doping of Y3+ into A-site is realized at reduced synthesis temperature, thus suppressing its further displacement during high-temperature sintering, consequently enhancing the membrane densification and improving the conductivity and stability. The anode-supported single cell exhibits a power density of 663 mW cm-2 at 600 °C and long-term stability for over 2000 h with negligible performance degradation. This study sheds light on protonic membrane sintering while offering an alternative strategy for protonic ceramic fuel cells development.

Enhancing Fast-Charge Capabilities in Solid-State Lithium Batteries through the Integration of High Li0.5La0.5TiO3 (LLTO) Content in the Lithium-Metal Anode.

Solid-state batteries (SSBs), which have high energy density and are safe, are recognized as an important field of study. However, the poor interfacial contact with high resistance, the dendrite problem, and the volume change of the metallic lithium anode prevent the use of SSBs. Li0.5La0.5TiO3 (LLTO) particles and molten lithium were used to create a high-performance LLTO-Li composite lithium with a sequential ion-conducting phase. With garnet electrolytes, this lithium has better wettability and reduced surface tension. To compensate for the lithium depletion that occurs during stripping, the Li-Ti phase with a high ionic diffusion coefficient that forms in the anode can rapidly transport lithium from the bulk to the solid-state interface, ensuring tight interface contact, preventing the formation of gaps, and homogenizing the current and Li+ flux. The LLTO-Li| LLZTO| LLTO-Li symmetric cell exhibits a good cyclic stability of 1000 h at room temperature, a low interfacial resistance of 22 Ω cm2, and a high critical current density of 1.2 mA cm-2. Furthermore, fully built cells with a LiFePO4 cathode showed outstanding cycling performance, maintaining 95% of their capacity after 900 cycles at 1 C and 92% capacity retention after 100 cycles at 2 C.

Accelerated deprotonation with a hydroxy-silicon alkali solid for rechargeable zinc-air batteries.

Transition metal oxides are promising electrocatalysts for zinc-air batteries, yet surface reconstruction caused by the adsorbate evolution mechanism, which induces zinc-ion battery behavior in the oxygen evolution reaction, leads to poor cycling performance. In this study, we propose a lattice oxygen mechanism involving proton acceptors to overcome the poor performance of the battery in the OER process. We introduce a stable solid base, hydroxy BaCaSiO4, onto the surfaces of PrBa0.5Ca0.5Co2O5+δ perovskite nanofibers with a one-step exsolution strategy. The HO-Si sites on the hydroxy BaCaSiO4 significantly accelerate proton transfer from the OH* adsorbed on PrBa0.5Ca0.5Co2O5+δ during the OER process. As a proof of concept, a rechargeable zinc-air battery assembled with this composite electrocatalyst is stable in an alkaline environment for over 150 hours at 5 mA cm-2 during galvanostatic charge/discharge tests. Our findings open new avenues for designing efficient OER electrocatalysts for rechargeable zinc-air batteries.

Enhancing potassium ions adsorption on mesoporous carbon spheres with abundant internal surface via engineering sulfur doping sites towards superior rate capability.

Mesoporous carbon spheres (MCSs) show great potential for using as high-performance anodes in potassium-ion batteries (PIBs). Design and synthesis of MCSs with suitable multiscale structures and heteroatom doping or co-doping in MCSs are successfully employed to optimize the ion and electron transportation, however, it is still a challenge to explore MCS-based anodes with satisfactory potassium storage performance. In this work, we report novel S-doped MCS samples with abundant internal surfaces for potassium storage. The S doping sites are controlled during the synthesis, and the effect of different doping sites on the potassium storage is systematically studied. It is found that S doping between the carbon layers enlarges interlayer spacing and facilitates potassium ion adsorption. Consequently, the optimized sample shows an excellent rate capability of 144 mAh/g at 5.0 A/g, and a high reversible specific capacity of 325 mAh/g after 100 cycles at 0.1 A/g with a capacity retention of 91.2%. The important role of element doping sites on ion adsorption and ion storage performance is confirmed by theoretical investigations. Controlling the doping sites in MCSs provides a new approach to designing high-performance electrodes for energy storage and conversion applications.