Achieving High-Capacity Cathode Presodiation Agent Via Triggering Anionic Oxidation Activity in Sodium Oxide.

Compensating for the irreversible loss of limited active sodium (Na) is crucial for enhancing the energy density of practical sodium-ion batteries (SIBs) full-cell, especially when employing hard carbon anode with initially lower coulombic efficiency. Introducing sacrificial cathode presodiation agents, particularly those that own potential anionic oxidation activity with a high theoretical capacity, can provide additional sodium sources for compensating Na loss. Herein, Ni atoms are precisely implanted at the Na sites within Na2O framework, obtaining a (Na0.89Ni0.05□0.06)2O (Ni-Na2O) presodiation agent. The synergistic interaction between Na vacancies and Ni catalyst effectively tunes the band structure, forming moderate Ni-O covalent bonds, activating the oxidation activity of oxygen anion, reducing the decomposition overpotential to 2.8 V (vs Na/Na+), and achieving a high presodiation capacity of 710 mAh/g≈Na2O (Na2O decomposition rate >80%). Incorporating currently-modified presodiation agent with Na3V2(PO4)3 and Na2/3Ni2/3Mn1/3O2 cathodes, the energy density of corresponding Na-ion full-cells presents an essential improvement of 23.9% and 19.3%, respectively. Further, not limited to Ni-Na2O, the structure-function relationship between the anionic oxidation mechanism and electrode-electrolyte interface fabrication is revealed as a paradigm for the development of sacrificial cathode presodiation agent.

An in situ exploration of how Fe/N/C oxygen reduction catalysts evolve during synthesis under pyrolytic conditions.

In pursuing cheap and effective oxygen reduction catalysts, the Fe/N/C system emerges as a promising candidate. Nevertheless, the structural transformations of starting materials into Fe- and N-doped carbon catalysts remains poorly characterized under pyrolytic conditions. Here, we explore the evolution of Fe species and track the formation of Fe-N4 site development by employing diverse in-situ diagnostic techniques. In-situ heating microscopy reveals the initial formation of FeOx nanoparticles and subsequent internal migration within the carbon matrix, which stops once FeOx is fully reduced. The migration and decomposition of nanoparticles then leads to carbon layer reconstruction. Experimental and theoretical analysis reveals size-dependent behavior of FeOx where nanoparticles below 7 nm readily release Fe atoms to form Fe-N4 while nanoparticles with sizes >10 nm tend to coalesce and impede Fe-N4 site formation. The work visualizes the pyrolysis process of Fe/N/C materials, providing theoretical guidance for the rational design of catalysts.

Unlocking Dynamic Solvation Chemistry and Hydrogen Evolution Mechanism in Aqueous Zinc Batteries.

Understanding the interfacial hydrogen evolution reaction (HER) is crucial to regulate the electrochemical behavior in aqueous zinc batteries. However, the mechanism of HER related to solvation chemistry remains elusive, especially the time-dependent dynamic evolution of the hydrogen bond (H-bond) under an electric field. Herein, we combine in situ spectroscopy with molecular dynamics simulation to unravel the dynamic evolution of the interfacial solvation structure. We find two critical change processes involving Zn-electroplating/stripping, including the initial electric double layer establishment to form an H2O-rich interface (abrupt change) and the subsequent dynamic evolution of an H-bond (gradual change). Moreover, the number of H-bonds increases, and their strength weakens in comparison with the bulk electrolyte under bias potential during Zn2+ desolvation, forming a diluted interface, resulting in massive hydrogen production. On the contrary, a concentrated interface (H-bond number decreases and strength enhances) is formed and produces a small amount of hydrogen during Zn2+ solvation. The insights on the above results contribute to deciphering the H-bond evolution with competition/corrosion HER during Zn-electroplating/stripping and clarifying the essence of electrochemical window widened and HER suppression by high concentration. This work presents a new strategy for aqueous electrolyte regulation by benchmarking the abrupt change of the interfacial state under an electric field as a zinc performance-enhancement criterion.

CO electrolysis to multicarbon products over grain boundary-rich Cu nanoparticles in membrane electrode assembly electrolyzers.

Producing valuable chemicals like ethylene via catalytic carbon monoxide conversion is an important nonpetroleum route. Here we demonstrate an electrochemical route for highly efficient synthesis of multicarbon (C2+) chemicals from CO. We achieve a C2+ partial current density as high as 4.35 ± 0.07 A cm-2 at a low cell voltage of 2.78 ± 0.01 V over a grain boundary-rich Cu nanoparticle catalyst in an alkaline membrane electrode assembly (MEA) electrolyzer, with a C2+ Faradaic efficiency of 87 ± 1% and a CO conversion of 85 ± 3%. Operando Raman spectroscopy and density functional theory calculations reveal that the grain boundaries of Cu nanoparticles facilitate CO adsorption and C - C coupling, thus rationalizing a qualitative trend between C2+ production and grain boundary density. A scale-up demonstration using an electrolyzer stack with five 100 cm2 MEAs achieves high C2+ and ethylene formation rates of 118.9 mmol min-1 and 1.2 L min-1, respectively, at a total current of 400 A (4 A cm-2) with a C2+ Faradaic efficiency of 64%.

Regulation Strategies for Fe-N-C and Co-N-C Catalysts for the Oxygen Reduction Reaction.

Proton exchange membrane fuel cells (PEMFCs) and alkaline membrane fuel cells (AEMFCs) have received great attention as energy devices of the next generation. Accelerating oxygen reduction reaction (ORR) kinetics is the key to improve PEMFC and AEMFC performance. Platinum-based catalysts are the most widely used catalysts for the ORR, but their high price and low abundance limit the commercialization of fuel cells. Non-noble metal-nitrogen-carbon (M-N-C) is considered to be the most likely material class to replace Pt-based catalysts, among which Fe-N-C and Co-N-C have been widely studied due to their excellent intrinsic ORR performance and have made great progress in the past decades. With the improvement of synthesis technology and a deeper understanding of the ORR mechanism, some reported Fe-N-C and Co-N-C catalysts have shown excellent ORR activity close to that of commercial Pt/C catalysts. Inspired by the progress, regulation strategies for Fe-N-C and Co-N-C catalysts are summarized in this Review from 5 perspectives: (1) coordinated atoms, (2) environmental heteroatoms and defects, (3) dual-metal active sites, (4) metal-based particle promoters, and (5) curved carbon layers. We also make suggestions on some challenges facing Fe-N-C and Co-N-C research.

Unveiling Low Temperature Assembly of Dense Fe-N4 Active Sites via Hydrogenation in Advanced Oxygen Reduction Catalysts.

The single-atom Fe-N-C is a prominent material with exceptional reactivity in areas of sustainable energy and catalysis research. It is challenging to obtain the dense Fe-N4 site without the Fe nanoparticles (NPs) sintering during the Fe-N-C synthesis via high-temperature pyrolysis. Thus, a novel approach is devised for the Fe-N-C synthesis at low temperatures. Taking FeCl2 as Fe source, a hydrogen environment can facilitate oxygen removal and dichlorination processes in the synthesis, efficiently favouring Fe-N4 site formation without Fe NPs clustering at as low as 360 °C. We shed light on the reaction mechanism about hydrogen promoting Fe-N4 formation in the synthesis. By adjusting the temperature and duration, the Fe-N4 structural evolution and site density can be precisely tuned to directly influence the catalytic behaviour of the Fe-N-C material. The FeNC-H2-360 catalyst demonstrates a remarkable Fe dispersion (8.3 wt %) and superior acid ORR activity with a half-wave potential of 0.85 V and a peak power density of 1.21 W cm-2 in fuel cell. This method also generally facilitates the synthesis of various high-performance M-N-C materials (M=Fe, Co, Mn, Ni, Zn, Ru) with elevated single-atom loadings.

Visualizing and Regulating Dynamic Evolution of Interfacial Electrolyte Configuration during De-solvation Process on Lithium-Metal Anode.

Acting as a passive protective layer, solid-electrolyte interphase (SEI) plays a crucial role in maintaining the stability of the Li-metal anode. Derived from the reductive decomposition of electrolytes (e.g., anion and solvent), the SEI construction presents as an interfacial process accompanied by the dynamic de-solvation process during Li-metal plating. However, typical electrolyte engineering and related SEI modification strategies always ignore the dynamic evolution of electrolyte configuration at the Li/electrolyte interface, which essentially determines the SEI architecture. Herein, by employing advanced electrochemical in situ FT-IR and MRI technologies, we directly visualize the dynamic variations of solvation environments involving Li+-solvent/anion. Remarkably, a weakened Li+-solvent interaction and anion-lean interfacial electrolyte configuration have been synchronously revealed, which is difficult for the fabrication of anion-derived SEI layer. Moreover, as a simple electrochemical regulation strategy, pulse protocol was introduced to effectively restore the interfacial anion concentration, resulting in an enhanced LiF-rich SEI layer and improved Li-metal plating/stripping reversibility.

The Lifetime of Hydroxyl Radical in Realistic Fuel Cell Catalyst Layer.

The lifetime of hydroxyl radicals (⋅OH) in the fuel cell catalyst layer remains uncertain, which hampers the comprehension of radical-induced degradation mechanisms and the development of longevity strategies for proton-exchange membrane fuel cells (PEMFCs). In this study, we have precisely determined that the lifetime of ⋅OH radicals can extend up to several seconds in realistic fuel cell catalyst layers. This finding reveals that ⋅OH radicals are capable of carrying out long-range attacks spanning at least a few centimeters during PEMFCs operation. Such insights hold great potential for enhancing our understanding of radical-mediated fuel cell degradation processes and promoting the development of durable fuel cell devices.

Graphitic Armor: A Natural Molecular Sieve for Robust Hydrogen Electroxidation.

Carbon coating layers have been found to improve the catalytic performance of transition metals, which is usually explained as an outcome of electronic synergistic effect. Herein we reveal that the defective graphitic carbon, with a unique interlayer gap of 0.342 nm, can be a highly selective natural molecular sieve. It allows efficient diffusion of hydrogen molecules or radicals both along the in-plane and out-of-plane direction, but sterically hinders the diffusion of molecules with larger kinetic diameter (e.g., CO and O2) along the in-plane direction. As a result, poisonous species lager than 0.342 nm are sieved out, even when their adsorption on the metal is thermodynamically strong; at the same time, the interaction between H2 and the metal is not affected. This natural molecular sieve provides a very chance for constructing robust metal catalysts for hydrogen-relevant processes, which are more tolerant to chemical or electrochemical oxidation or CO-relevant poisoning.

Constructing the Polymer Molecules to Regulate the Electrode/Electrolyte Interface to Enhance Lithium-Metal Battery Performance.

Lithium-ion batteries, with high energy density and long cycle life, have become the battery of choice for most vehicles and portable electronic devices; however, energy density, safety and cycle life require further improvements. Single-functional group electrolyte additives are very limited in practical applications, a ternary polymer bifunctional electrolyte additive copolymer (acrylonitrile-butyl hexafluoro methacrylate- poly (ethylene glycol) methacrylate- methyl ether) (PMANHF) was synthesized by free radical polymerization of acrylonitrile, 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate and poly (ethylene glycol) methyl ether methacrylate. A series of characterizations show that in Li metal anodes, the preferential reduction of PMANHF is conducive to the formation of a uniform and stable solid electrolyte interphase layer, and Li deposition is uniform and dense. At the NCM811 cathode, a film composed of LiF- and Li3N-rich is formed at the cathode-electrolyte interface, mitigating the side reaction at the interface. At 1.0 mA cm-2, the Li/Li cell can be stabilized for 1000 cycles. In addition, the Li/NCM811 cell can stabilize 200 cycles with a cathode capacity of 153.7 mAh g-1, with the capacity retention of 89.93 %, at a negative/positive capacity ratio of 2.5. This study brings to light essential ideas for the fabrication of additives for lithium-metal batteries.

Gradient Interphase Engineering Enabled by Anionic Redox for High-Voltage and Long-Life Li-Ion Batteries.

Intelligent utilization of the anionic redox reaction (ARR) in Li-rich cathodes is an advanced strategy for the practical implementation of next-generation high-energy-density rechargeable batteries. However, due to the intrinsic complexity of ARR (e.g., nucleophilic attacks), the instability of the cathode-electrolyte interphase (CEI) on a Li-rich cathode presents more challenges than typical high-voltage cathodes. Here, we manipulate CEI interfacial engineering by introducing an all-fluorinated electrolyte and exploiting its interaction with the nucleophilic attack to construct a gradient CEI containing a pair of fluorinated layers on a Li-rich cathode, delivering enhanced interfacial stability. Negative/detrimental nucleophilic electrolyte decomposition has been efficiently evolved to further reinforce CEI fabrication, resulting in the construction of LiF-based indurated outer shield and fluorinated polymer-based flexible inner sheaths. Gradient interphase engineering dramatically improved the capacity retention of the Li-rich cathode from 43 to 71% after 800 cycles and achieved superior cycling stability in anode-free and pouch-type full cells (98.8% capacity retention, 220 cycles), respectively.

Hydrogen Spillover Accelerates Electrocatalytic Semi-hydrogenation of Acetylene in Membrane Electrode Assembly Reactor.

Electrocatalytic acetylene semi-hydrogenation (EASH) offers a promising and environmentally friendly pathway for the production of C2H4, a widely used petrochemical feedstock. While the economic feasibility of this route has been demonstrated in three-electrode systems, its viability in practical device remains unverified. In this study, we designed a highly efficient electrocatalyst based on a PdCu alloy system utilizing the hydrogen spillover mechanism. The catalyst achieved an operational current density of 600 mA cm-2 in a zero-gap membrane electrode assembly (MEA) reactor, with the C2H4 selectivity exceeding 85%. This data confirms the economic feasibility of EASH in real-world applications. Furthermore, through in situ Raman spectroscopy and theoretical calculations, we elucidated the catalytic mechanism involving interfacial hydrogen spillover. Our findings underscore the economic viability and potential of EASH as a greener and scalable approach for C2H4 production, thus advancing the field of electrocatalysis in sustainable chemical synthesis.

High-Entropy Mn/Fe-Based Layered Cathode with Suppressed P2-P'2 Transition and Low-Strain for Fast and Stable Sodium Ion Storage.

Mn/Fe-based layered oxides are deemed to be a highly suitable cathode for sodium-ion batteries (SIBs) due to their high capacity and abundant Mn/Fe resources, but they still suffer from a complicated phase transition and large volume variation. To conquer these problems, high-entropy Mn/Fe-based layered oxide P2-Na0.67Mn0.5Fe0.334Cu0.045Mg0.014Ti0.014Al0.014Zr0.014Sn0.014O2 (Mn-Fe-HEO) is rationally designed and fabricated. When used as a cathode for SIB, high-entropy Mn-Fe-HEO exhibits much higher reversible capacity and better rate capability than low-entropy Na0.67Mn0.5Fe0.334Cu0.164O2 (Mn-Fe-LEO) within a wide voltage range of 1.5-4.3 V. Ex situ X-ray diffraction combined with diffusion kinetics tests and microstructural characterizations demonstrate that high-entropy enhanced structural stability effectively prevents the Jahn-Teller distortion of Mn3+, stabilizes the Na+ diffusion channels, and enables the smooth transfer of more working Na+. These lead to a stable and fast redox electrochemistry in high-entropy Mn-Fe-HEO. This work deepens the understanding of the relationship between high-entropy structure and performance and provides important guidance for the rational design of future high-entropy layered cathodes.

Implanting Transition Metal into Li2 O-Based Cathode Prelithiation Agent for High-Energy-Density and Long-Life Li-Ion Batteries.

Compensating the irreversible loss of limited active lithium (Li) is essentially important for improving the energy-density and cycle-life of practical Li-ion battery full-cell, especially after employing high-capacity but low initial coulombic efficiency anode candidates. Introducing prelithiation agent can provide additional Li source for such compensation. Herein, we precisely implant trace Co (extracted from transition metal oxide) into the Li site of Li2 O, obtaining (Li0.66 Co0.11 □0.23 )2 O (CLO) cathode prelithiation agent. The synergistic formation of Li vacancies and Co-derived catalysis efficiently enhance the inherent conductivity and weaken the Li-O interaction of Li2 O, which facilitates its anionic oxidation to peroxo/superoxo species and gaseous O2 , achieving 1642.7 mAh/g~Li2O prelithiation capacity (≈980 mAh/g for prelithiation agent). Coupled 6.5 wt % CLO-based prelithiation agent with LiCoO2 cathode, substantial additional Li source stored within CLO is efficiently released to compensate the Li consumption on the SiO/C anode, achieving 270 Wh/kg pouch-type full-cell with 92 % capacity retention after 1000 cycles.

One-Step Surface-to-Bulk Modification of High-Voltage and Long-Life LiCoO2 Cathode with Concentration Gradient Architecture.

Raising the charging cut-off voltage of layered oxide cathodes can improve their energy density. However, it inevitably introduces instabilities regarding both bulk structure and surface/interface. Herein, exploiting the unique characteristics of high-valence Nb5+ element, a synchronous surface-to-bulk-modified LiCoO2 featuring Li3 NbO4 surface coating layer, Nb-doped bulk, and the desired concentration gradient architecture through one-step calcination is achieved. Such a multifunctional structure facilitates the construction of high-quality cathode/electrolyte interface, enhances Li+ diffusion, and restrains lattice-O loss, Co migration, and associated layer-to-spinel phase distortion. Therefore, a stable operation of Nb-modified LiCoO2 half-cell is achieved at 4.6 V (90.9% capacity retention after 200 cycles). Long-life 250 Wh kg-1 and 4.7 V-class 550 Wh kg-1 pouch cells assembled with graphite and thin Li anodes are harvested (both beyond 87% after 1600 and 200 cycles). This multifunctional one-step modification strategy establishes a technological paradigm to pave the way for high-energy density and long-life lithium-ion cathode materials.

Lattice Engineering on Li2CO3-Based Sacrificial Cathode Prelithiation Agent for Improving the Energy Density of Li-Ion Battery Full-Cell.

Developing sacrificial cathode prelithiation technology to compensate for active lithium loss is vital for improving the energy density of lithium-ion battery full-cells. Li2CO3 owns high theoretical specific capacity, superior air stability, but poor conductivity as an insulator, acting as a promising but challenging prelithiation agent candidate. Herein, extracting a trace amount of Co from LiCoO2 (LCO), a lattice engineering is developed through substituting Li sites with Co and inducing Li defects to obtain a composite structure consisting of (Li0.906Co0.043▫0.051)2CO2.934 and ball milled LiCoO2 (Co-Li2CO3@LCO). Notably, both the bandgap and Li─O bond strength have essentially declined in this structure. Benefiting from the synergistic effect of Li defects and bulk phase catalytic regulation of Co, the potential of Li2CO3 deep decomposition significantly decreases from typical >4.7 to ≈4.25 V versus Li/Li+, presenting >600 mAh g-1 compensation capacity. Impressively, coupling 5 wt% Co-Li2CO3@LCO within NCM-811 cathode, 235 Wh kg-1 pouch-type full-cell is achieved, performing 88% capacity retention after 1000 cycles.

FeN4 Active Sites Electronically Coupled with PtFe Alloys for Ultralow Pt Loading Hybrid Electrocatalysts in Proton Exchange Membrane Fuel Cells.

The exorbitant cost of Pt-based electrocatalysts and the poor durability of non-noble metal electrocatalysts for proton exchange membrane fuel cells limited their practical application. Here, FeN4 active sites electronically coupled with PtFe alloys (PtFe-FeNC) were successfully prepared by a vapor deposition strategy as an ultralow Pt loading (0.64 wt %) hybrid electrocatalyst. The FeN4 sites on the FeNC matrix are able to effectively anchor the PtFe alloys, thus inhibiting their aggregation during long-life cycling. These PtFe alloys, in turn, can efficiently restrain the leaching of the FeN4 sites from the FeNC matrix. Thus, the PtFe-FeNC demonstrated an improved Pt mass activity of 2.33 A mgPt-1 at 0.9 V toward oxygen reduction reaction, which is 12.9 times higher than that of commercial Pt/C (0.18 A mgPt-1). It demonstrated great stability, with the Pt mass activity decreasing by only 9.4% after 70,000 cycles. Importantly, the fuel cell with an ultralow Pt loading in the cathode (0.012 mgPt cm-2) displays a high Pt mass activity of 1.75 A mgPt-1 at 0.9 ViR-free, which is significantly better than commercial MEA (0.25 A mgPt-1). Interestingly, PtFe-FeNC catalysts possess enhanced durability, exhibiting a 12.5% decrease in peak power density compared to the 51.7% decrease of FeNC.

Manipulated Fluoro-Ether Derived Nucleophilic Decomposition Products for Mitigating Polarization-Induced Capacity Loss in Li-Rich Layered Cathode.

Electrolyte engineering is a fascinating choice to improve the performance of Li-rich layered oxide cathodes (LRLO) for high-energy lithium-ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro-ether. By benefit of the decomposition of fluoro-ether under nucleophilic O-related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro-ether acts as "sutures", ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V-class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high-energy anionic redox related cathode systems.

Carbon-coated silica supported palladium for hydrogen production from formic acid - Exploring the influence of strong metal support interaction.

Hydrogen energy is one of the most promising energy carriers to solve the increasingly severe energy crisis. Formic acid decomposition (FAD) solves the storage and transportation problems of hydrogen gas since hydrogen can be produced from aqueous formic acid under mild conditions. To efficiently convert formic acid to hydrogen gas, chemical and structural modification of Pd nanoparticles or supports have been carried out, especially introducing the strong metal support interaction (SMSI). Herein, we synthesized core-shell structured SiO2@SC compounds as the supports to introduce SMIS to Pd/PdO nanoparticles. The relationship between FAD activity and SMSI is investigated. The SMSI between Pd/PdO nanoparticles and SiO2/SC is adjusted by altering the thickness of the carbon layer. The X-ray photoelectron spectroscopy shows that owing to the strong electron-attracting ability SiO2 core contributes to leading the Pd0 active site in an electron-deficient state. The thickness of the carbon layer controls the ratio of Pd0/PdO, which enhances the anti-poisoning ability of the catalyst. Owing to the electron-deficient state of Pd0 and optimal ratio of Pd0/PdO, the hydrogen desorption rate of FAD on Pd is enhanced, and the turn over frequency of Pd/SiO2@SC-1:3 catalyst reaches 1138 h-1, which is ten times higher than that of the pristine Pd/SC catalyst. These results are believed to guide the design and development of highly active Pd-based catalysts for hydrogen generation via FAD.

Protecting Li-metal in O2 atmosphere by a sacrificial polymer additive in Li-O2 batteries.

Li-O2 batteries (LOBs) with Li-metal as the anode are characterized by their high theoretical energy density of 3500 W h kg-1 and are thus considered next-generation batteries with an unlimited potential. However, upon cycling in a harsh O2 atmosphere, the poor-quality solid electrolyte interphase (SEI) film formed on the surface of the Li-metal anode cannot effectively suppress the shuttle effect from O2, superoxide species, protons, and soluble side products. These issues lead to aggravated Li-metal corrosion and hinder the practical development of LOBs. In this work, a polyacrylamide-co-polymethyl acrylate (PAMMA) copolymer was innovatively introduced in an ether-based electrolyte as a sacrificial additive. PAMMA was found to preferentially decompose and promote the formation of a dense and Li3N-rich SEI film on the Li-metal surface, which could effectively prohibit the shuttle effect from a series of detrimental species in the Li-O2 cell during the discharge/charge process. Using PAMMA, well-protected Li-metal in a harsh O2 atmosphere and significantly enhanced cycling performance of the Li-O2 cell could be achieved. Thus, the use of a sacrificial polymer additive provides a promising strategy for the effective protection of Li-metal in Li-O2 cells in a severe O2 atmosphere during practical applications.