ACS Applied Energy Materials最新文献

Hydrometallurgical processing of spent lithium-ion battery cathode mass with organic acids has traditionally relied on the addition of hydrogen peroxide as a reducing agent to convert Co³⁺ and Mn⁴⁺ into soluble form. Here we show that, for real industrial high-nickel black mass (NCA with a minor NMC admixture), this recommendation not only fails but proves counterproductive. Without any external reducing agent, 2.0 M malonic acid (70 °C, 2 h, S:L = 1:30) achieves recoveries of 90.3 wt % Ni, 97.7 wt % Mn, 99.9 wt % Li, and 69.3 wt % Co through the intrinsic reductive activity of its active methylene group. The addition of H₂O₂ progressively lowers transition-metal recovery (Ni from 90.3 to 50.9 wt %, Co from 69.3 to 45.8 wt % at 8 vol %), whereas Li recovery remains essentially unchanged (98–100 wt %). Using a combination of independent methods (XRD, SEM-EDS, FT-IR), the decrease is shown to arise not from cathode passivation but from Fenton-like oxidative degradation of malonic acid to oxalic acid, initiated by the impurity metals Cu and Fe, with subsequent reprecipitation of the dissolved Ni²⁺ and Co²⁺ as the mixed oxalate dihydrate (Ni,Co)C₂O₄·2H₂O. The radical nature of the process is confirmed by complete suppression of the effect upon addition of methanol (an HO• scavenger) and by its absence when H₂O₂ is replaced with mild reductants (ascorbic acid, glucose), which afford nearly quantitative Ni and Co recovery. These findings revise the role of H₂O₂ in systems with organic chelating acids and, at the same time, offer a single-step route to an oxalate precursor for cathode materials.

A nitrogen-doped reduced graphene oxide (rGO)/BiVO₄ nanocomposite has been prepared through a hydrothermal route as a photocatalyst for selective photoreduction of CO₂ into formic acid. This study specifically examines how N doping of the rGO/BiVO₄ nanocomposite governs the selectivity and yield of the C1 product. Two-dimensional nanohexagonal BiVO₄, BiVO₄ loaded with varying wt % rGO, and rGO/BiVO₄ doped with varying wt % N are synthesized and characterized by UV–vis absorption, XRD, PL, XPS, BET, SEM, EDX, TEM, EIS, and Mott–Schottky measurements. Among all the compositions examined, the sample with 1.5 wt % N doping on 2.5 wt % rGO/BiVO₄ stood out, with an average particle size of about 6–25 nm, a red-shifted absorption edge at 659.39 nm, a narrowed band gap of 2.06 eV, the least electron–hole recombination, and improved charge-carrier separation and mobility; this sample delivered the highest photocatalytic activity, reaching 593.24 ± 5.15 μmol g_cat.^–1 h^–1 with a 100% selective yield of formic acid. Doping 1.5% nitrogen into the (2.5%)rGO/BiVO₄ photocatalyst also raises the number of defect sites available for capturing CO₂, boosting the selective yield of photocatalytic CO₂ conversion into formic acid, with an AQY of roughly 0.148 ± 0.00064%. Both the experiments and DFT calculations show that N doping narrows the band gap and shifts the VBM toward the CBM through the introduced N-2p orbitals and further predict hybridization among the overlapping N-2p, O-2p, Bi-6p, and V-3d orbitals near the Fermi level. The proposed mechanism indicates that photogenerated electrons migrate from BiVO₄ toward the doped N atoms through the rGO network to fill the electron vacancy in the N-2p orbital. Acting as an electron acceptor, rGO separates the photo-excited electron–hole pairs across the junction interface and promotes adsorption of CO₂ molecules onto the photocatalyst surface. Doping (2.5%)rGO/BiVO₄ with 1.5% N raises the selective formic acid yield 2-fold relative to undoped (2.5%)rGO/BiVO₄.

The energy transition requires the development of efficient and decarbonized energy storage and conversion systems. In this context, dihydrogen (H₂) is a promising energy carrier. Ideally, it should be produced through water electrolysis using intermittent renewable energy sources (solar, wind, etc.) to be further utilized in a fuel cell to generate electricity. To date, proton-exchange membrane fuel cells are the most efficient and mature H₂ conversion technology. However, a major drawback relies on the use of noble metals, such as platinum (Pt), as electrocatalysts for the electrochemical reactions involved in this device. Deploying these technologies requires the development of an efficient recycling pathway to reduce pressure on these natural resources. This study aims to identify an optimized way to electrochemically recover Pt salts from a Pt/C catalyst in alkaline conditions. A three-step electrochemical protocol was applied in the presence of ammonia as a complexing agent with the objective to favor Pt dissolution while preventing both Pt particles detachment and Pt redeposition. As a result, this process demonstrated a high yield (i.e., ≥90%) of Pt leaching on the model Pt/C catalyst. Finally, the selected protocol was transferred to a membrane electrode assembly (MEA) aged in realistic conditions as a proof of concept.

Poly(oxindole biphenylene) ion-solvating membranes (POBP-ISMs) have emerged as promising candidate membrane materials for use in hydrogen production through alkaline water electrolysis (AWE), owing to their exceptional alkaline stability. However, their dense architecture leads to insufficient exposure of functional groups, resulting in low electrolyte uptake and substantial ion transport resistance, which collectively limit ionic conductivity and compromise the durable, high-efficiency performance of AWE. To overcome this limitation, we prepared an asymmetric porous POBP (AP-POBP) membrane using a two-step nonsolvent-induced phase separation (NIPS) method. The AP-POBP membrane has a two-layer structure, including a thin and dense surface layer and a highly porous support layer. This unique structure simultaneously enhances ionic conductivity, superior gas barrier, and high chemical stability performance of ISMs. Noticeably, the Ni-based AWE with the obtained AP-POBP ISM achieved a high current density of 2.4 A cm⁻² at 2.0 V, superior to that of a dense membrane (0.25 A cm⁻²). It maintained stable operation for 800 h at 2 A cm⁻² with no appreciable membrane degradation. These results demonstrate that the introduction of an asymmetric porous two-layer architecture represents a simple yet effective strategy for designing advanced ISMs with precisely controlled porous morphologies, enabling superior comprehensive performance in AWE applications.

Although alkaline zinc/ferricyanide flow batteries (AZFFBs) perform well under ambient conditions, their low-temperature operation is severely limited by the freezing of aqueous electrolytes and the resulting deterioration of ion transport and reaction kinetics. At low temperatures, the extensive hydrogen-bond (H-bond) network among H₂O molecules promotes the formation of an ordered frozen phase, leading to sluggish electrochemical kinetics. Herein, we report a cryogenic electrolyte formulated with potassium acetate (KAc) and urea as additives. The strong interactions between the additives and H₂O molecules effectively break the original H-bonding network, thereby lowering the freezing-point while preserving high ionic conductivity even at extremely low temperatures. Density functional theory calculations combined with spectroscopic analyses reveal that KAc acts as a strong H-bonding acceptor and urea as a strong H-bonding donor. They synergistically disrupt the tetrahedral H-bonding network among H₂O molecules. The optimized electrolyte (0.9 M KAc and 4.0 M urea, denoted as K.U.) achieves a substantially depressed freezing-point of –18.9 °C and retains excellent fluidity at –20 °C without any precipitation. Electrochemical measurements confirm that the additives do not compromise the redox activity of the [Fe(CN)₆]^3–/4– couple, which maintains good reversibility even at –20 °C. By virtue of the disrupted H-bonding network and enhanced ionic conductivity, AZFFBs using the K.U. catholyte exhibit outstanding low-temperature performance. At –20 °C and 20 mA cm^–2, the AZFFB operated stably for more than 2500 cycles (>1200 h), delivering average coulombic efficiency, voltage efficiency, and energy efficiency values of 99.8%, 88.3%, and 88.1%, respectively, with 83.2% capacity retention after 2500 cycles. This synergistic additive strategy, which relies on precise modulation of the H-bonding network, offers a general pathway toward high-performance cryogenic electrolytes and significantly facilitates the practical deployment of AZFFBs in cold climates.

Tin-based halide perovskites are promising lead-free alternatives for optoelectronic applications, yet their practical implementation is limited by the facile oxidation of Sn(II) to Sn(IV), which compromises environmental stability. Inspired by the success of triple-cation engineering in Pb-based perovskites, we explored the mixed A-site series FA_0.80MA_0.20–xCs_xSnBr₃ (x = 0–0.20) and the corresponding Pb analogues, synthesized via a solvent-free mechanochemical route. Powder X-ray diffraction confirmed the formation of phase-pure perovskite compounds, while diffuse reflectance spectroscopy showed only minor changes in the optical band gap (E_g) upon A-site mixing. Multinuclear solid-state nuclear magnetic resonance (NMR) spectroscopy, including high-resolution two-dimensional double-quantum single-quantum ¹H NMR spectra, demonstrated homogeneous mixing of formamidinium (FA), methylammonium (MA), and cesium cations without phase segregation or clustering. Quantification of ¹H and ¹³C NMR spectra confirmed the intended cationic compositions, whereas ¹³³Cs, ¹¹⁹Sn, and ²⁰⁷Pb NMR spectra revealed the influence of cation mixing on the local chemical environments. Comparative ⁷⁹Br nuclear quadrupolar resonance spectroscopy spectra on the Pb analogues further supported a random cation distribution. Ambient stability studies showed that Cs₂SnBr₆ is the primary degradation product of the Sn series and that moderate Cs incorporation partially improves structural stability, while higher loadings promote degradation. Finally, time-domain terahertz spectroscopy revealed distinct lattice-dynamical responses in the Sn and Pb series, indicating stronger lattice polarization in the Pb compounds and lattice stiffening accompanied by partial stabilization in the Sn compounds upon Cs incorporation. These results establish a direct correlation among homogeneous A-site mixing, local structure, lattice dynamics, and stability, providing mechanistic insight into the design of stable lead-free tin halide perovskites.

Manganese-based oxides are attractive cathode materials for aqueous magnesium-ion batteries (AMIBs) due to their high theoretical capacity, abundant resources, and environmental friendliness but suffer from poor conductivity, manganese dissolution, and structural degradation during cycling. In this work, CuMn₂O₄ is proposed as a dual redox-active cathode material for AMIBs. During discharge, lattice copper ions are extracted and in-situ reduced to metallic copper, which contributes to capacity and enhances electronic conductivity. Consequently, CuMn₂O₄ delivers highly enhanced capacity (211 mAh g⁻¹ at 100 mA g⁻¹) and cycling stability compared to monometallic Mn₃O₄. Moreover, the aqueous Mg∥CuMn₂O₄ full cell achieves an average discharge voltage of 1.80 V and stable cycling for over 50 cycles. This study confirms the feasibility of CuMn₂O₄ as a high-performance cathode material for AMIBs and provides insights for developing low-cost, high-performance multivalent-ion battery cathode materials.

Aqueous aluminum-ion batteries (AIBs) promise safe and low-cost energy storage but are hindered by pervasive hydrogen evolution and aluminum anode corrosion due to strong Al³⁺ hydration. We introduce hexamethylphosphoramide (HMPA), a high-donor-number additive, to reconstruct this solvation structure and enable reversible Al electrochemistry. Vibrational and NMR spectroscopies show that HMPA coordinates directly to Al³⁺, displacing inner shell water ligands and disrupting the extended hydrogen bond network, thereby lowering water activity at the electrode interface. Increasing the HMPA concentration markedly enhances electrolyte wetting on aluminum surfaces, with contact angles decreasing from 80.1° in pure aqueous electrolyte to 45.2° at 60 vol % HMPA. Immersion studies reveal robust corrosion suppression with 40 vol % HMPA. In full cells pairing aluminum anodes with polyaniline (PANI) cathodes, the optimized 40 vol % HMPA electrolyte yields an initial specific capacity of 194.9 mAh/g at 100 mA/g, an initial Coulombic efficiency of 81.4%, and a capacity retention of 61.3 mAh/g after 200 cycles with 99.1% efficiency. Kinetic studies via cyclic voltammetry indicate predominantly surface-controlled pseudocapacitive behavior, contributing 81.0% of the charge storage at 0.9 mV/s. This additive-driven solvation engineering strategy provides a scalable, effective pathway toward practical, high-performance aqueous multivalent-ion batteries.

Copper-based catalysts uniquely drive the electrochemical CO₂ reduction reaction (CO₂RR) to value-added hydrocarbons, but poor product selectivity, inadequate stability, and mass-transfer limitations at high current densities restrict their practical application. Herein, a structure–composition synergistic regulation strategy was proposed to fabricate a bimodal nanoporous CuPd–Ag tandem catalyst via nanoporous engineering and bimetallic alloying. By tailoring the bimodal nanoporous morphology and tandem heterointerfaces, the optimized catalyst exhibits remarkable CO₂-to-CH₄ conversion performance, achieving a CH₄ Faradaic efficiency of 58.3% and a total current density of 230 mA cm^–2. Operando Raman spectroscopy and DFT-calculated free energy profiles reveal a dual-promotion tandem mechanism: *CO intermediates from CO₂ activation on Ag sites rapidly spill over to adjacent Cu–Pd sites to build a high-concentration *CO microenvironment, while adsorbed *H on Pd atoms in the Cu–Pd alloy lattice facilitates the rate-determining *CO hydrogenation to *CHO, thus accelerating selective CH₄ evolution. The deactivation during long-term operation was also elucidated. Under cathodic polarization, the catalyst underwent surface structural reconstruction, Cu and Ag dissolution, and subsequent collapse of the porous framework, collectively leading to deactivation. This work establishes the structure–activity relationship of tandem configurations, providing theoretical insights for designing highly selective and stable CO₂RR electrocatalysts toward practical CO₂ utilization.

Graphitic carbon nitride (g-C₃N₄) holds great potential for photocatalytic hydrogen evolution, yet suffers from insufficient light harvesting, fast charge recombination, and low surface area. In this work, nitro-functionalized worm-like chain carbon nitride with benzene ring domains (CCNB) was rationally fabricated via copolymerization of melamine and p-nitrobenzoic acid. Systematic characterizations and density functional theory (DFT) calculations demonstrate that benzene rings coupled with electron-withdrawing nitro groups exert a synergistic effect on interfacial charge transport, wherein the π-electron delocalization is extended by the benzene structure while the nitro functional group acts as an effective driver for electron transfer. Meanwhile, the introduction of nitro groups and benzene ring effectively narrows the band gap of CCNB, strengthening its optical absorption capacity. Consequently, the optimal CCNB-0.15 sample exhibits an outstanding photocatalytic hydrogen evolution rate of 2312 μmol·g⁻¹·h⁻¹, which is 10.9 times higher than that of pristine g-C₃N₄. This study provides a feasible dual-modification strategy coupling benzene ring and surface nitro functionalization to surmount the inherent drawbacks of bulk g-C₃N₄, offering a pathway for designing high-performance carbon nitride-based photocatalysts toward efficient solar hydrogen production.