Coordination Engineering of N,O Co-Doped Cu Single Atom on Porous Carbon for High Performance Zinc Metal Anodes

Traditional challenges of poor cycling stability and low Coulombic efficiency in Zinc (Zn) metal anodes have limited their practical application. To overcome these issues, this work introduces a single metal-atom design featuring atomically dispersed single copper (Cu) atoms on 3D nitrogen (N) and oxygen (O) co-doped porous carbon (CuNOC) as a highly reversible Zn host. The CuNOC structure provides highly active sites for initial Zn nucleation and further promotes uniform Zn deposition. The 3D porous architecture further mitigates the volume changes during the cycle with homogeneous Zn²⁺ flux. Consequently, CuNOC demonstrates exceptional reversibility in Zn plating/stripping processes over 1000 cycles at 2 and 5 mA cm⁻² with a fixed capacity of 1 mAh cm⁻², while achieving stable operation and low voltage hysteresis over 700 h at 5 mA cm⁻² and 5 mAh cm⁻². Furthermore, density functional theory calculations show that co-doping N and O on porous carbon with atomically dispersed single Cu atoms creates an efficient zincophilic site for stable Zn nucleation. A full cell with the CuNOC host anode and high loading V₂O₅ cathode exhibits outstanding rate-capability up to 5 A g⁻¹ and a stable cycle life over 400 cycles at 0.5 A g⁻¹.     

Unveiling The Mechanism of The Dendrite Nucleation and Growth in Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (ZIBs) exhibit great potential for next-generation energy storage devices. However, significant challenges exist, including the uncontrollable formation of Zn dendrite and side reactions during zinc stripping and plating. The mechanism of Zn dendrite nucleation has yet to be fully understood. In this work, the first principles simulations are used to investigate the Zn dendrite formation process. The unintentionally adsorbed O²⁻ and OH⁻ ions are the inducing factors for Zn dendrite nucleation and growth on the Zn (0001) plane due to significantly increased Zn diffusion barriers. A top-down method is demonstrated to suppress the dendrite using delaminated V₂CT_x to capture O²⁻ and OH⁻ ions thanks to reduced Zn diffusion barriers. The experimental results revealed significantly suppressed Zn dendrite nucleation and growth, resulting in a layer-by-layer deposit/stripping of Zn. Based on the electrochemical evaluations, the V₂CT_x-coated Zn composite delivers a high coulombic efficiency of 99.3% at 1.0 mAh cm⁻². Furthermore, the full cell achieves excellent cyclic performance of 93.6% capacity retention after 2000 cycles at 1 A g⁻¹. This strategy has broad scalability and can be widely applied in designing metallic anodes for rechargeable batteries.     

Steel Anti-Corrosion Strategy Enables Long-Cycle Zn Anode

The progress of aqueous zinc batteries (AZBs) is limited by the poor cycling life due to Zn anode instability, including dendrite growth, surface corrosion, and passivation. Inspired by the anti-corrosion strategy of steel industry, a compounding corrosion inhibitor (CCI) is employed as the electrolyte additive for Zn metal anode protection. It is shown that CCI can spontaneously generate a uniform and ≈30 nm thick solid-electrolyte interphase (SEI) layer on Zn anode with a strong adhesion via Zn O bonding. This SEI layer efficiently prohibits water corrosion and guides homogeneous Zn deposition without obvious dendrite formation. This enables reversible Zn deposition and dissolution for over 1100 h under the condition of 1 mA cm⁻² and 1 mAh cm⁻² in symmetric cells. The Zn-MnO₂ full cells with CCI-modified electrolyte deliver an ultralow capacity decay rate (0.013% per cycle) at 0.5 A g⁻¹ over 1000 cycles. Such an innovative strategy paves a low-cost way to achieve AZBs with long lifespan.     

Robust Hybrid Solid Electrolyte Interface Induced by Zn-Poor Electric Double Layer for A Highly Reversible Zinc Anode

Aqueous Zn-ion batteries (AZIBs) show great potential in new energy storage devices due to low cost, inherent safety, and environmental friendliness. However, the severe dendrites and side reactions on the anode greatly constrain their practical application. Herein, a novel colloidal electrolyte composed of ZnSO₄ and sodium carboxymethyl cellulose (CMC-Na) has been developed for inhibiting dendrite growth on Zn anode. Molecular dynamics (MD) simulation confirms that CMC-Na alters the electric double layer (EDL) structure of Zn anode surface to reduce the content of water and SO₄²⁻ and inhibit side reactions. More importantly, an organic/inorganic hybrid solid electrolyte interface (SEI) layer is in situ constructed during the cycling, which enables ultrastable Zn plating/stripping (> 2000 h) under high current density (5 mA cm⁻², 5 mAh cm⁻²) and high coulombic efficiency (99.8%) for more than 1000 cycles. Meanwhile, zinc-ion hybrid capacitors (ZIHCs) with the colloidal electrolyte exhibit a favorable capacitance retention of 97% after 15000 cycles at the current density of 2 A g⁻¹. Even at a high current density of 5 A g⁻¹, it still has a capacitance retention of 96% after 30000 cycles. This study presents a novel electrolyte strategy for the formation of ultrastable electrode-electrolyte interfaces in AZIBs.     

Artificial Solid‐Electrolyte Interphase Enabled High‐Capacity and Stable Cycling Potassium Metal Batteries

Secondary batteries based on earth‐abundant potassium metal anodes are attractive for stationary energy storage. However, suppressing the formation of potassium metal dendrites during cycling is pivotal in the development of future potassium metal‐based battery technology. Herein, a promising artificial solid‐electrolyte interphase (ASEI) design, simply covering a carbon nanotube (CNT) film on the surface of a potassium metal anode, is demonstrated. The results show that the spontaneously potassiated CNT framework with a stable self‐formed solid‐electrolyte interphase layer integrates a quasi‐hosting feature with fast interfacial ion transport, which enables dendrite‐free deposition of potassium at an ultrahigh capacity (20 mAh cm^?2). Remarkably, the potassium metal anode exhibits an unprecedented cycle life (over 1000 cycles, over 2000 h) at a high current density of 5 mA cm^?2 and a desirable areal capacity of 4 mAh cm^?2. Dendrite‐free morphology in carbon‐fiber and carbon‐black‐based ASEI for potassium metal anodes, which indicates a broader promise of this approach, is also observed.     

Going beyond Intercalation Capacity of Aqueous Batteries by Exploiting Conversion Reactions of Mn and Zn electrodes for Energy‐Dense Applications

The recent trend in zinc (Zn) anode aqueous batteries has been to explore layered structures like manganese dioxides and vanadium oxides as Zn‐ion intercalation hosts. These structures, although novel, face limitations like their layered counterparts in lithium (Li)‐ion batteries, where the capacity is limited to the host's intercalation capacity. In this paper, a new strategy is proposed in enabling new generation of energy dense aqueous‐based batteries, where the conversion reactions of rock salt/spinel manganese oxides and carbon nanotube‐nested nanosized Zn electrodes are exploited to extract significantly higher capacity compared to intercalation systems. Accessing the conversion reactions allows to achieve high capacities of 750 mAh g^?1 (≈30 mAh cm^?2) from manganese oxide (MnO) and 810 mAh g^?1 (≈30 mAh cm^?2) from nanoscale Zn anodes, respectively. The high areal capacities help to attain unprecedented energy densities of 210 Wh per L‐cell and 320 Wh per kg‐total (398 Wh per kg‐active) from aqueous MnO|CNT‐Zn batteries, which allows an assessment of its viable use in a small‐scale automobile.     

Compact 3D Copper with Uniform Porous Structure Derived by Electrochemical Dealloying as Dendrite‐Free Lithium Metal Anode Current Collector

The development of lithium (Li) metal anodes Li metal batteries faces huge challenges such as uncontrolled Li dendrite growth and large volume change during Li plating/stripping, resulting in severe capacity decay and high safety hazards. A 3D porous copper (Cu) current collector as a host for Li deposition can effectively settle these problems. However, constructing a uniform and compact 3D porous Cu structure is still an enormous challenge. Herein, an electrochemical etching method for Cu–Zinc (Zn) alloy is reported to precisely engrave a 3D Cu structure with uniform, smooth, and compact porous network. Such a continuous structure endows 3D Cu excellent mechanical properties and high electrical conductivity. The uniform and smooth pores with a large internal surface area ensures well dispersed current density for homogeneous Li metal deposition and accommodation. A smooth and stable solid electrolyte interphase is formed and meanwhile Li dendrites and dead Li are effectively suppressed. The Li metal anode conceived 3D Cu current collector can stably cycle for 400 h under an Li plating/stripping capacity of 1 mA h cm^?2 and a current density of 1 mA cm^?2. The Li@3D Cu||LiFePO₄ full cells present excellent cycling and rate performances. The electrochemical dealloying is a robust method to construct 3D Cu current collectors for dendrite‐free Li metal anodes.     

Gradient-Structured and Robust Solid Electrolyte Interphase In Situ Formed by Hydrated Eutectic Electrolytes for High-Performance Zinc Metal Batteries

The mechanically and electrochemically stable and ionically conducting solid electrolyte interphase (SEI) is important for the stabilization of metal anodes. Since SEIs are originally absent in aqueous zinc metal batteries (AZMBs), it is very challenging to suppress water-induced side reactions and dendrite growth of Zn metal anodes (ZMAs). Herein, a gradient-structured and robust solid gradient SEI, consisting of B,O-inner and F,O-exterior layer, in situ formed by hydrated eutectic electrolyte for the homogeneous and reversible Zn deposition, is demonstrated. Moreover, the molar ratio of acetamide to Zn salt is modulated to prohibit the water activity and the hydrolysis of BF₄⁻ as well as to achieve high ionic conductivity owing to the regulation of the solvation sheath of Zn²⁺. Consequently, the eutectic electrolyte allows Zn||Zn symmetric cells to achieve a cycling lifespan of over 4400 h at 0.5 mA cm⁻² as well as Zn||PANI full cells to deliver a high capacity retention of 73.2% over 4000 cycles at 1 A g⁻¹ and to demonstrate the stable operation at low temperatures. This work provides the rational design for the hydrated eutectic electrolyte and the corresponding gradient SEIs for dendrite-free and stable Zn anodes even under harsh conditions.     

Pseudo‐Zn–Air and Zn‐Ion Intercalation Dual Mechanisms to Realize High‐Areal Capacitance and Long‐Life Energy Storage in Aqueous Zn Battery

Aqueous zinc batteries are considered as promising alternatives to lithium ion batteries owing to their low cost and high safety. However, the developments of state‐of‐the‐art zinc‐ion batteries (ZIB) and zinc–air batteries (ZAB) are limited by the unsatisfied capacities and poor cycling stabilities, respectively. It is of significance in utilizing the long‐cycle life of ZIB and high capacity of ZAB to exploit advanced energy storage systems. Herein, a bulk composite of graphene oxide and vanadium oxide (V₅O₁₂·6H₂O) as cathode material for aqueous Zn batteries in a mild electrolyte is employed. The battery performance is demonstrated to arise from a combination of the reversible cations insertion/extraction in vanadium oxide and especially the electrochemical redox reactions on the surface functional groups of graphene oxide (named as pseudo‐Zn–air mechanism). Along with adjusting the hydroxyl content on the surface of graphene oxide, the specific capacity is significantly increased from 342 mAh g^?1 to a maximum of 496 mAh g^?1 at 100 mA g^?1. The surface‐controlled kinetics occurring in the bulk composite ensure a high areal capacity of 10.6 mAh cm^?2 at a mass loading of 26.5 mg cm^?2, and a capacity retention of 84.7% over 10 000 cycles at a high current density of 10 A g^?1.     

Ultrathin Reed Membranes: Nature's Intimate Ion-Regulation Skins Safeguarding Zinc Metal Anodes in Aqueous Batteries

The practical realization of aqueous zinc-ion batteries relies crucially on effective interphases governing Zn electrodeposition chemistry. In this study, an innovative solution by introducing an ultrathin (≈2 µm) biomass membrane as an intimate artificial interface, functioning as nature's ion-regulation skin to protect zinc metal anodes is proposed. Capitalizing on the inherent properties of natural reed membrane, including multiscale ion transport tunnels, abundant ─OH groups, and remarkable mechanical integrity, the reed membrane demonstrates efficacy in regulating uniform and rapid Zn²⁺ transport, promoting desolvation, and governing Zn (002) plane electrodeposition. Importantly, a unique in situ electrochemical Zn─O bond formation mechanism between the reed membrane and Zn electrode upon cycling is elucidated, resulting in a robustly adhered interface covering on the zinc anode surface, ultimately ensuring remarkable dendrite-free and highly reversible Zn anodes. Consequently, the approach achieves a prolonged cycle life for over 1450 h at 3 mA cm⁻²/1.5 mAh cm⁻² in symmetric Zn//Zn cells. Moreover, exceptional cyclic performance (88.95%, 4000 cycles) is obtained in active carbon-based cells with an active mass loading of 5.8 mg cm⁻². The approach offers a cost-effective and environmentally friendly strategy for achieving stable and reversible zinc anodes for aqueous batteries.     

Interrelation Between External Pressure,SEI Structure,and Electrodeposit Morphology in an Anode-Free Lithium Metal Battery

The interrelation is explored between external pressure (0.1, 1, and 10 MPa), solid electrolyte interphase (SEI) structure/morphology, and lithium metal plating/stripping behavior. To simulate anode-free lithium metal batteries (AF-LMBs) analysis is performed on “empty” Cu current collectors in standard carbonate electrolyte. Lower pressure promotes organic-rich SEI and macroscopically heterogeneous, filament-like Li electrodeposits interspersed with pores. Higher pressure promotes inorganic F-rich SEI with more uniform and denser Li film. A “seeding layer” of lithiated pristine graphene (pG@Cu) favors an anion-derived F-rich SEI and promotes uniform metal electrodeposition, enabling extended electrochemical stability at a lower pressure. State-of-the-art electrochemical performance is achieved at 1MPa: pG-enabled half-cell is stable after 300 h (50 cycles) at 1 mA cm⁻² rate −3 mAh cm⁻² capacity (17.5 µm plated/stripped), with cycling Coulombic efficiency (CE) of 99.8%. AF-LMB cells with high mass loading NMC622 cathode (21 mg cm⁻²) undergo 200 cycles with a CE of 99.4% at C/5-charge and C/2-discharge (1C = 178 mAh g⁻¹). Density functional theory (DFT) highlights the differences in the adsorption energy of solvated-Li⁺ onto various crystal planes of Cu (100), (110), and (111), versus lithiated/delithiated (0001) graphene, giving insight regarding the role of support surface energetics in promoting SEI heterogeneity.     

Nanoporous CaCO3 Coatings Enabled Uniform Zn Stripping/Plating for Long‐Life Zinc Rechargeable Aqueous Batteries

Zn‐based batteries are safe, low cost, and environmentally friendly, as well as delivering the highest energy density of all aqueous battery systems. However, the application of Zn‐based batteries is being seriously hindered by the uneven electrostripping/electroplating of Zn on the anodes, which always leads to enlarged polarization (capacity fading) or even cell shorting (low cycling stability). How a porous nano‐CaCO₃ coating can guide uniform and position‐selected Zn stripping/plating on the nano‐CaCO₃‐layer/Zn foil interfaces is reported here. This Zn‐deposition‐guiding ability is mainly ascribed to the porous nature of the nano‐CaCO₃‐layer, since similar functionality (even though relatively inferior) is also found in Zn foils coated with porous acetylene black or nano‐SiO₂ layers. Furthermore, the potential application of this strategy is demonstrated in Zn|ZnSO₄+MnSO₄|CNT/MnO₂ rechargeable aqueous batteries. Compared with the ones with bare Zn anodes, the battery with a nano‐CaCO₃‐coated Zn anode delivers a 42.7% higher discharge capacity (177 vs 124 mAh g^?1 at 1 A g^?1) after 1000 cycles.     

Quantum Dot Based Heterostructures for Unassisted Photoelectrochemical Hydrogen Generation

TiO₂ hollow nanowires (HNWs) and nanoparticles (NPs) constitute promising architectures for QDs sensitized photoanodes for H₂ generation. We sensitize these structures with CdS/CdSe quantum dots by two different methods (chemical bath deposition, CBD and succesive ionic layer adsorption and reaction, SILAR) and evaluate the performance of these photoelectrodes. Remarkable photocurrents of 4 mA·cm and 8 mA·cm^?2 and hydrogen generation rates of 40 ml·cm^?2·day^?1 and 80 ml·cm^?2·day^?1 have been obtained in a three electrode configuration with sacrificial hole scavengers (Na₂S and Na₂SO₃), for HNWs and NPs respectively, which is confirmed through gas analysis. More importantly, autonomous generation of H₂ (20 ml·cm^?2·day^?1 corresponding to 2 mA·cm^?2 photocurrent) is obtained in a two electrode configuration at short circuit under 100 mW·cm^?2 illumination, clearly showing that these photoanodes can produce hydrogen without the assistance of any external bias. To the best of the authors' knowledge, this is the highest unbiased solar H₂ generation rate reported for these of QDs based heterostructures. Impedance spectroscopy measurements show similar electron density of trap states below the TiO₂ conduction band while the recombination resistance was higher for HNWs, consistently with the much lower surface area compared to NPs. However, the conductivity of both structures is similar, in spite of the one dimensional character of HNWs, which leaves some room for improvement of these nanowired structures. The effect of the QDs deposition method is also evaluated. Both structures show remarkable stability without any appreciable photocurrent loss after 0.5 hour of operation. The findings of this study constitute a relevant step towards the feasibility of hydrogen generation with wide bandgap semiconductors/quantum dots based heterostructures.     

Boosting Ion Diffusion and Charge Transfer by Zincophilic Accordion Arrays to Achieve Ultrafast Aqueous Zinc Metal Batteries

A key challenge to apply aqueous zinc metal batteries (AZMBs) as next-generation energy storage device is to improve the rechargeability at high current densities, which is needed to circumvent slowly ion diffusion in anode and sluggish charge transfer of Zn²⁺. Herein, a zincophilic accordion array derived from MOF is developed as zinc host for simultaneously boosted ion diffusion and charge transfer. The designed host is prepared by etching and disproportionation reactions, the abundant zincophilic Sn sites with nano-size uniform disperse on accordion arrays nanosheets (Sn-AA). Then a composite Zn anode (Sn-AA@Zn) is obtained by compacting Sn-AA host with zinc power (Zn-P). The Sn-AA@Zn anode has an ultra-low activation energy (37.1 kJ mol⁻¹) and nucleation overpotential (10 mV), achieving fast charge transfer of Zinc deposition. In addition, the cycle life of the symmetric cell with Sn-AA@Zn anode exceeds 13 000 cycles at 50 mA cm⁻², which is 32 times than that of the Zn-P anode. And the full cell with Sn-AA@Zn anode and MnO₂ cathode maintains a capacity of 122 mAh g⁻¹ after 5000 cycles at 5 Ag⁻¹. Hopefully, the 3D anode based on Sn-AA@Zn accordion array and Zn-P has significantly improved the rechargeability of AZMB at high current density.     

An Iodine-Chemisorption Binder for High-Loading and Shuttle-Free Zn–Iodine Batteries

Aqueous zinc–iodine (Zn–I₂) batteries have attracted considerable research interest as an alternative energy storage system due to their high specific capacity, intrinsic safety, and low cost. However, the notorious shuttle effect of soluble polyiodides causes severe capacity loss and poor electrochemical reversibility, restricting their practical usage. Herein, this study reports a bifunctional binder (polyacrylonitrile copolymer, as known as LA133) with strong iodine-chemisorption capability for aqueous Zn–I₂ batteries to suppress polyiodide shuttling. From both calculation and experimental data, this study reveals that the amide and carboxyl groups in LA133 binder can strongly bond to polyiodides, significantly immobilizing them at cathode side. As a result, fewer byproducts, slower hydrogen evolution, and lesser Zn dendrite in the Zn–I₂ battery are observed. Consequently, the battery shows high specific capacity (202.8 mAh g⁻¹) with high iodine utilization efficiency (96.1%), and long cycling lifespan (2700 cycles). At the high mass loading of 7.82 mg cm⁻², the battery can still retain 83.3% of its initial capacity after 1000 cycles. The specific capacity based on total cathode slurry mass reaches 71.2 mAh g⁻¹, higher than most of the recent works. The strategy opens a new avenue to address the shuttling challenge of Zn–I₂ batteries through bifunctional binder.     

Solvation Modulation and Reversible SiO2-Enriched Interphase Enabled by Deep Eutectic Sol Electrolytes for Low-Temperature Zinc Metal Batteries

Zinc metal batteries (ZMBs) hold great promise for large-scale energy storage in renewable solar and wind farms. However, their widespread application is hindered by poor stability and unsatisfactory low-temperature performance, attributed to issues such as dendrite formation, strong Zn²⁺-H₂O coordination, and electrolyte freezing. Herein, a deep eutectic sol electrolyte (DESE) is proposed by mixing SiO₂ nanoparticles with a solution composed of 1,3-dioxolane (DOL) and Zn(ClO₄)₂·6H₂O for stable low-temperature ZMBs. By substituting the strong Zn²⁺- H₂O coordination with favorable Zn²⁺-DOL coordination, the DESE exhibits exceptional antifreezing capability at temperatures beyond −40 °C. The formation of Si-O-Zn²⁺ bond near SiO₂ nanoparticles further improves the low-temperature performance of the DESE by decreasing Zn²⁺ desolvation energy. Moreover, the SiO₂ nanoparticles co-plating/co-stripping with Zn metal, forming a reversible and homogeneous SiO₂-enriched interphase to protect the Zn anode from dendrite growth and interfacial side reactions. Remarkably, the DESE-based ZMB full cells exhibit significantly prolonged cycle life of 8000 cycles at 1 A g⁻¹ at 25 °C and 700 cycles at 0.2 A g⁻¹ at -40 °C. This work provides a promising strategy to design advanced electrolytes for practical low-temperature ZMBs.     

Accessing the Two‐Electron Charge Storage Capacity of MnO2 in Mild Aqueous Electrolytes

Rechargeable batteries based on MnO₂ cathodes, able to operate in mild aqueous electrolytes, have attracted attention due to their appealing features for the design of low‐cost stationary energy storage devices. However, the charge/discharge mechanism of MnO₂ in such media is still a matter of debate. Here, an in‐depth quantitative spectroelectrochemical analysis of MnO₂ thin‐films provides a set of unrivaled mechanistic insights. A major finding is that charge storage occurs through the reversible two‐electron faradaic conversion of MnO₂ into Mn²⁺ in the presence of a wide range of weak Brønsted acids, including the [Zn(H₂O)₆]²⁺ or [Mn(H₂O)₆]²⁺ complexes present in aqueous Zn/MnO₂ batteries. Furthermore, it is shown that buffered electrolytes loaded with Mn²⁺ are ideal to achieve highly reversible conversion of MnO₂ with both high gravimetric capacity and remarkably stable charging/discharging potentials. In the most favorable case, a record gravimetric capacity of 450 mA·h·g^?1 is obtained at a high rate of 1.6 A·g^?1, with a Coulombic efficiency close to 100% and a MnO₂ utilization of 84%. Overall, the present results challenge the common view on MnO₂ the charge storage mechanism in mild aqueous electrolytes and underline the benefit of buffered electrolytes for high‐performance rechargeable aqueous batteries.     

Inducing the Preferential Growth of Zn (002) Plane for Long Cycle Aqueous Zn-Ion Batteries

Uncontrolled growth of Zn dendrites is the main reason for the short-circuit failure of aqueous Zn-ion batteries. Using electrolyte additives to manipulate the crystal growth is one of the most convenient strategies to mitigate the dendrite issue. However, most additives would be unstable during cycling due to the structural reconstruction of the deposition layer. Herein, it is proposed to use 1-butyl-3-methylimidazolium cation (BMIm⁺ ion) as an electrolyte additive, which could steadily induce the preferential growth of (002) plane and inhibit the formation of Zn dendrites. Specifically, BMIm⁺ ion will be preferentially adsorbed on (100) and (101) planes of Zn anodes, forcing Zn²⁺ ion to deposit on the (002) plane, thus inducing the preferential growth of the (002) plane and forming a flat and compact deposition layer. As a result, the Zn anode cycles for 1000 h at10 mA cm⁻² and 10 mAh cm⁻² as well as a high Coulombic efficiency of 99.8%. Meanwhile, the NH₄V₄O₁₀||Zn pouch cell can operate stably for 240 cycles at 0.4 A g⁻¹. The BMIm⁺ ion additive keeps a stable effect on the structural reconstruction of the Zn anode during the prolonged cycling.     

Thermal Regime and Stability of Jurumirim Reservoir (Paranapanema River,São Paulo,Brazil)

Thermal regime and stability in Jurumirim Reservoir (São Paulo, Brazil) were studied for a year. Isothermy and thermal stratification were observed from June to September and from October to March, respectively. The annual heat budget was 14.0 Kcal · cm⁻² and average heat gain per day was 67.2 cal · cm⁻² · day⁻¹. Maximum stability and wind work reached 324.2 and 3,037.5 g · cm · cm⁻², respectively. According to thermal structure and heat content, Jurumirim Reservoir was classified as a warm tropical monomictic lake.     

Translational diffusion of lipid monomers determined by spin label electron spin resonance

The collision rates between spin-labelled valeric acid in water, and between the corresponding mixed-chain, spin-labelled phosphatidylcholine in water-methanol mixtures, and also between spin-labelled phosphatidylcholine monomers and micelles in water have been determined from the spin-spin broadening of the electron spin resonance spectrum. In each case the second order rate constants are consistent with a diffusion-controlled process. For spin-labelled valeric acid in water the translational diffusion coefficient at 20°C is 3.4 · 10⁻⁶ cm² · s⁻¹, and for spin-labelled phosphatidylcholine varies between 2.3 · 10⁻⁶ and 3.8 · 10⁻⁶ cm² · s⁻¹ within the range 44 to 88 wt% methanol. The spin-labelled phosphatidylcholine monomer diffusion coefficient in water at 20°C is 2.4 · 10⁻⁶ cm² · s⁻¹, deduced from the monomer-micelle association rate, with an activation energy of 4.0 kcal · mol⁻¹. The much slower on-rates for association of lipid monomers with phospholipid bilayer vesicles reported in the literature, therefore indicate that incorporation into bilayers is not a diffusion-controlled process.