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Fluid‐rock dissolution occurs ubiquitously in geological systems. Surface‐volume scaling is central to predicting overall dissolution rate R involved in modeling dissolution processes. Previous works focused on single‐phase environments but overlooked the multiphase‐flow effect. Here, through limestone‐based microfluidics experiments, we establish a fundamental link between dissolution regimes and scaling laws. In regime I (uniform), the scaling is consistent with classic law, and a satisfactory prediction of R can be obtained. However, the scaling for regime II (localized) deviates significantly from classic law. The underlying mechanism is that the reaction‐induced gas phase forms a layer, acting as a barrier that hinders contact between the acid and rock. Consequently, the error between measurement and prediction continuously amplifies as dissolution proceeds; the predictability is poor. We propose a theoretical model that describes the regime transition, exhibiting excellent agreement with experimental results. This work offers guidance on the usage of scaling law in multiphase flow environments. Plain Language Summary Fluid‐rock dissolution is ubiquitous in natural and engineered systems, including karst formation, geological carbon sequestration, and acid stimulation. Recent developed method for CO2 sequestration relies on mineralization, which transforms CO2 into carbonate minerals through geochemical reactions involving dissolution. The precise modeling of dissolution processes at the continuum‐scale is dependent on the estimation of the overall dissolution rate using surface‐volume scaling laws. This important scaling law is always established in a single‐phase system. Here, through limestone‐based microfluidics experiments, we find that the scaling is significantly affected by the dissolution regime in a multiphase flow environment. When the injection rate is lower, and the geometry is more homogeneous, the dissolution regime adheres to classic law. On the other hand, when the flow is stronger and the heterogeneity exhibits, the dissolution scaling significantly diverges. Our discovery indicates that a layer of CO2 gas attaches to the uneven surface, causing a shielding effect on the dissolution and resulting in a notable deviation. Through establishing a theoretical model for the regime transition, this work offers guidance on the usage of scaling law across various dissolution scenarios. The newly developed scaling can enhance dissolution modeling precision in multiphase flow‐dissolution systems such as geologic carbon sequestration. Key Points We observe two regimes, and the scaling in regime II deviates significantly from classic law, with a poor predictability of dissolution rate We identify a barrier effect in real rock samples that inhibits the contact of acid and rock for the deviation of scaling in regime II We propose a theoretical model for regime transition that offers guidance on the usage of scaling law in multiphase environments

Reactive flow through geological fractures under stress is fundamental to subsurface hydrology. In this flow‐stress‐dissolution system, free‐surface dissolution within voids increases permeability, whereas pressure dissolution at contacting asperities combined with mechanical deformation seals the fracture. The interplay between these mechanisms controlling fracture sealing or opening remains to be explored. Here, we integrate numerical simulations with theoretical analysis to examine the coupled mechanical‐chemical processes. We develop a flow‐stress‐dissolution modeling approach with the incorporation of pressure dissolution, free‐surface dissolution and mechanical deformation for fractures in homogeneous mineral systems. Comparison with previously experiments demonstrates the ability of this approach and highlights the significant role of pressure dissolution for fracture sealing. Through extensive simulations with a wide range of flow rates, reaction rates and normal stresses, we find that stress induced‐mechanical compaction enhances the positive feedback mechanisms between free‐surface dissolution and solute transport, promoting the development of dissolution channels. Our analysis of permeability evolution under various stresses and dissolution patterns reveals that fracture sealing can occur in uniform and compact patterns depending on stress, whereas fracture opening spontaneously occurs in wormholes. Through theoretical analysis of the interplay between pressure dissolution and free‐surface dissolution, we propose a theoretical model for the occurrence of fracture sealing. A generalized phase diagram is then established that can effectively describe fracture sealing under varying flow rates, reaction rates, and normal stress conditions. Our work provides a foundation for assessing fracture leakage risks in subsurface engineering and holds practical implications for geological carbon and hydrogen storage.

Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn 2 O 4 cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn 2 O 4 exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn 2 O 4 with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries. To unlock the potential of Mn-based cathode materials, the fast capacity fading process has to be first understood. Here the authors utilize advanced characterization techniques to look at a spinel LiMn 2 O 4 system, revealing that a combination of irreversible structural transformations and Mn dissolution takes responsibility.

Transition metal dissolution in cathode active material for Li-based batteries is a critical aspect that limits the cycle life of these devices. Although several approaches have been proposed to tackle this issue, this detrimental process is not yet overcome. Here, benefitting from the knowledge developed in the semiconductor research field, we apply an epitaxial method to construct an atomic wetting layer of LaTMO 3 (TM = Ni, Mn) on a LiNi 0.5 Mn 1.5 O 4 cathode material. Experimental measurements and theoretical analyses confirm a Stranski–Krastanov growth, where the strained wetting layer forms under thermodynamic equilibrium, and it is self-limited to monoatomic thickness due to the competition between the surface energy and the elastic energy. Being atomically thin and crystallographically connected to the spinel host lattices, the LaTMO 3 wetting layer offers long-term suppression of the transition metal dissolution from the cathode without impacting its dynamics. As a result, the epitaxially-engineered cathode material enables improved cycling stability (a capacity retention of about 77% after 1000 cycles at 290 mA g −1 ) when tested in combination with a graphitic carbon anode and a LiPF 6 -based non-aqueous electrolyte solution. Transition metal dissolution from cathode materials limits the cycle life of Li-ion batteries. Here, the authors report an atomic-thin protecting layer on the surface of a high-voltage cathode material, enabling long-term Li-ion battery cycling.

AbstractThe paper presents post-mortem analysis of commercial LiFePO4 battery cells, which are aged at 55 °C and − 20 °C using dynamic current profiles and different depth of discharges (DOD). Post-mortem analysis focuses on the structure of the electrodes using atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the chemical composition changes using energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results show that ageing at lower DOD results in higher capacity fading compared to higher DOD cycling. The anode surface aged at 55 °C forms a dense cover on the graphite flakes, while at the anode surface aged at − 20 °C lithium plating and LiF crystals are observed. As expected, Fe dissolution from the cathode and deposition on the anode are observed for the ageing performed at 55 °C, while Fe dissolution and deposition are not observed at − 20 °C. Using atomic force microscopy (AFM), the surface conductivity is examined, which shows only minor degradation for the cathodes aged at − 20 °C. The cathodes aged at 55 °C exhibit micrometer size agglomerates of nanometer particles on the cathode surface. The results indicate that cycling at higher SOC ranges is more detrimental and low temperature cycling mainly affects the anode by the formation of plated Li.Graphic abstract

Seawater electrolysis powered by renewable electricity provides an attractive strategy for producing green hydrogen 1 , 2 , 3 , 4 – 5 . However, direct seawater electrolysis faces many challenges, primarily arising from corrosion and competing reactions at the anode caused by the abundance of halide ions (Cl − , Br − ) in seawater 6 . Previous studies 3 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 – 14 on seawater electrolysis have mainly focused on the anode development, because the cathode operates at reducing potentials, which is not subject to electrode dissolution or chloride corrosion reactions during seawater electrolysis 11 , 15 . However, renewable energy sources are intermittent, variable and random, which cause frequent start–shutdown operations if renewable electricity is used to drive seawater electrolysis. Here we first unveil dynamic evolution and degradation of seawater splitting cathode in intermittent electrolysis and, accordingly, propose construction of a catalyst’s passivation layer to maintain the hydrogen evolution performance during operation. An in situ-formed phosphate passivation layer on the surface of NiCoP–Cr 2 O 3 cathode can effectively protect metal active sites against oxidation during frequent discharge processes and repel halide ion adsorption on the cathode during shutdown conditions. We demonstrate that electrodes optimized using this design strategy can withstand fluctuating operation at 0.5 A cm − 2 for 10,000 h in alkaline seawater, with a voltage increase rate of only 0.5% khr −1 . The newly discovered challenge and our proposed strategy herein offer new insights to facilitate the development of practical seawater splitting technologies powered by renewable electricity. Construction of a phosphate passivation layer on the surface of a cathode to withstand fluctuating operation in alkaline seawater is proposed following understanding the mechanism behind the dynamic evolution and degradation of cathode in intermittent electrolysis.

Two major challenges hinder the advance of aqueous zinc metal batteries for sustainable stationary storage: (1) achieving predominant Zn-ion (de)intercalation at the oxide cathode by suppressing adventitious proton co-intercalation and dissolution, and (2) simultaneously overcoming Zn dendrite growth at the anode that triggers parasitic electrolyte reactions. Here, we reveal the competition between Zn 2+ vs proton intercalation chemistry of a typical oxide cathode using ex-situ/ operando techniques, and alleviate side reactions by developing a cost-effective and non-flammable hybrid eutectic electrolyte. A fully hydrated Zn 2+ solvation structure facilitates fast charge transfer at the solid/electrolyte interface, enabling dendrite-free Zn plating/stripping with a remarkably high average coulombic efficiency of 99.8% at commercially relevant areal capacities of 4 mAh cm −2 and function up to 1600 h at 8 mAh cm −2 . By concurrently stabilizing Zn redox at both electrodes, we achieve a new benchmark in Zn-ion battery performance of 4 mAh cm −2 anode-free cells that retain 85% capacity over 100 cycles at 25 °C. Using this eutectic-design electrolyte, Zn | |Iodine full cells are further realized with 86% capacity retention over 2500 cycles. The approach represents a new avenue for long-duration energy storage. Achieving high-performance aqueous Zn-metal batteries is a challenge. Here, authors report a eutectic electrolyte that concurrently enables selective Zn 2+ intercalation at the cathode and highly reversible Zn metal plating/stripping, resulting in a benchmark high-areal capacity Zn anode-free cell.

HighlightsThe Zn/MnO2 cell with inorganic colloidal electrolyte demonstrates unprecedented durability over 1000 cycles.For the cathode, the presence of the protective film can inhibit the dissolution of manganese element and the formation of irreversible by-products.For the anode, it can reduce the corrosion and de-solvation energy, inhibit the growth of dendrite and irreversible by-products.Zinc-ion batteries (ZIBs) is a promising electrical energy storage candidate due to its eco-friendliness, low cost, and intrinsic safety, but on the cathode the element dissolution and the formation of irreversible products, and on the anode the growth of dendrite as well as irreversible products hinder its practical application. Herein, we propose a new type of the inorganic highly concentrated colloidal electrolytes (HCCE) for ZIBs promoting simultaneous robust protection of both cathode/anode leading to an effective suppression of element dissolution, dendrite, and irreversible products growth. The new HCCE has high Zn2+ ion transference number (0.64) endowed by the limitation of SO42−, the competitive ion conductivity (1.1 × 10–2 S cm−1) and Zn2+ ion diffusion enabled by the uniform pore distribution (3.6 nm) and the limited free water. The Zn/HCCE/α-MnO2 cells exhibit high durability under both high and low current densities, which is almost 100% capacity retention at 200 mA g−1 after 400 cycles (290 mAh g−1) and 89% capacity retention under 500 mA g−1 after 1000 cycles (212 mAh g−1). Considering material sustainability and batteries’ high performances, the colloidal electrolyte may provide a feasible substitute beyond the liquid and all-solid-state electrolyte of ZIBs.

The long-standing challenges facing Pt-based alloy catalysts in oxygen reduction reactions (ORRs) are rapid oxidation and loss of transition metal/Pt in proton exchange membrane fuel cells (PEMFCs). In this work, we report a concept of “covalentization” in intermetallic L1 0 -PtMM’ (M = Fe, Co, Ni and M’ = one of the 4 th -period elements (from Ti to Ge)) alloys to enhance their electrochemical stability. Specifically, the formation of a quasi-covalent bond network in L1 0 -PtMM’ due to the less occupied antibonding states induced by high d -band positions of M’ elements (e.g., Ti, V, Cr) enhances atomic bond order and strength, diminishing Co anodic dissolution via strengthened Pt/Co-M’ bonds and reducing Co cathodic corrosion by inhibiting Pt oxidation through an electron buffering effect. The developed L1 0 -PtCoCr/C catalysts show a high mass activity (MA = 1.27 A mg Pt −1 ) and rated power (16.5 W mg Pt −1 ) in PEMFCs at a low total Pt loading of 0.075 mg Pt  cm −2 . The catalysts also exhibit high electrochemical stability with ~3% and 5% loss of MA and rated power after 30,000 accelerated durability testing cycles and projects a lifetime of about 42,000 hours. Pt-based alloy cathode catalysts in proton exchange membrane fuel cells face persistent challenges, including rapid oxidation and loss of transition metal/Pt. Here, the authors report a covalentization concept in intermetallic L1 0 -structure Pt-based alloys to boost stability in fuel cells.

A drug dissolution profile is one of the most critical dosage form characteristics with immediate and controlled drug release. Comparing the dissolution profiles of different pharmaceutical products plays a key role before starting the bioequivalence or stability studies. General recommendations for dissolution profile comparison are mentioned by the EMA and FDA guidelines. However, neither the EMA nor the FDA provides unambiguous instructions for comparing the dissolution curves, except for calculating the similarity factor f2. In agreement with the EMA and FDA strategy for comparing the dissolution profiles, this manuscript provides an overview of suitable statistical methods (CI derivation for f2 based on bootstrap, CI derivation for the difference between reference and test samples, Mahalanobis distance, model-dependent approach and maximum deviation method), their procedures and limitations. However, usage of statistical approaches for the above-described methods can be met with difficulties, especially when combined with the requirement of practice for robust and straightforward techniques for data evaluation. Therefore, the bootstrap to derive the CI for f2 or CI derivation for the difference between reference and test samples was selected as the method of choice.