A Zn-based catalyst with high oxygen reduction activity and anti-poisoning property for stable seawater batteries.

Seawater batteries (SWBs) are a key part of the future underwater energy network for maritime safety and resource development due to their high safety, long lifespan, and eco-friendly nature. However, the complicated seawater composition and pollution, such as the S2-, usually poison the catalyst and lead to the degradation of the battery performance. Here, Zn single-atom catalysts (SACs) were demonstrated as effective oxygen reduction reaction catalysts with high anti-poisoning properties by density functional theory calculation and the Zn SACs anchoring on an N, P-doped carbon substrate (Zn-SAC@PNC) was synthesized by a one-pot strategy. Zinc active sites ensure the anti-poisoning property toward S2-, and N, P-doped carbon helps improve the activity. Therefore, Zn-SAC@PNC exhibits superior activity (E1/2: 0.87 V, Tafel slope: 69.5 mV dec-1) compared with Pt/C and shows a lower decay rate of the voltage after discharge in lean-oxygen natural seawater. In the presence of S2-, Zn-SAC@PNC can still maintain its original catalytic activity, which ensures the stable operation of SWBs in the marine environment with sulfur-based pollutants. This study provides a new strategy to design and develop efficient cathode materials for SWBs.

Unraveling the Catalyst-Solvent Interactions in Lean-Electrolyte Sulfur Reduction Electrocatalysis for Li-S Batteries.

Efficient catalyst design is important for lean-electrolyte sulfur reduction in Li-S batteries. However, most of the reported catalysts were focused on catalyst-polysulfide interactions, and generally exhibit high activity only with a large excess of electrolyte. Herein, we proposed a general rule to boost lean-electrolyte sulfur reduction by controlling the catalyst-solvent interactions. As evidenced by synchrotron-based analysis, in situ spectroscopy and theoretical computations, strong catalyst-solvent interaction greatly enhances the lean-electrolyte catalytic activity and battery stability. Benefitting from the strong interaction between solvent and cobalt catalyst, the Li-S battery achieves stable cycling with only 0.22 % capacity decay per cycle with a low electrolyte/sulfur mass ratio of 4.2. The lean-electrolyte battery delivers 79 % capacity retention compared with the battery with flooded electrolyte, which is the highest among the reported lean-electrolyte Li-S batteries.

Enhanced Oxygen Accumulation for a Hydrophobic Cathode in Lean-Oxygen Seawater Batteries.

The unsatisfactory oxygen reduction reaction (ORR) kinetics caused by the inherent lean-oxygen marine environment brings low power density for metal-dissolved oxygen seawater batteries (SWBs). In this study, we propose a seawater/electrode interfacial engineering strategy by constructing a hydrophobic coating to realize enhanced mass transfer of dissolved oxygen for the fully immersed cathode of SWBs. Accumulation of dissolved oxygen from seawater to the catalyst is particularly beneficial for improving the ORR performance under lean-oxygen conditions. As a result, SWB assembled with a hydrophobic cathode achieved a power density of up to 2.32 mW cm-2 and sustained discharge at 1.3 V for 250 h. Remarkably, even in environments with an oxygen concentration of 4 mg L-1, it can operate at a voltage approximately 100 mV higher than that of an unmodified SWB. The introduction of a hydrophobic interface enhances the discharge voltage and power of SWBs by improving interfacial oxygen mass transfer, providing new insights into improving the underwater ORR performance for practical SWBs.

Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering.

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.

Molecular catalysts with electronic axial stretching for high-performance lean-oxygen seawater batteries.

A dissolved-oxygen seawater battery (SWB) can generate electricity by reducing dissolved oxygen and sacrificing the metal anode at different depths and temperatures in the ocean, acting as the basic unit of spatially underwater energy networks for future maritime exploration. However, most traditional oxygen reduction reaction (ORR) catalysts are out of work at such ultralow dissolved oxygen concentration. Here, we proposed that the electronic axial stretching of the catalyst is essentially responsible for enhancing the catalyst's sensitivity to dissolved oxygen. By modulating the lattice of iron phthalocyanine (FePc) as a model catalyst, the unique electronic axial stretching in the z-direction of planar FePc molecules was realized to achieve a boosted adsorption and electron transfer and result in a much improved ORR activity in lean-oxygen seawater environment. The peak power density of a homemade SWB using a practical carbon brush electrode decorated by the FePc is estimated to be as high as 3 W L-1. These results provide inspiring insights into the interaction between the catalyst and complicated seawater environment, and propose the electronic axial stretching as an effective indicator for the rational design of catalysts to be used in extremely lean-oxygen environment.

Tuning Zn-Ion Solvation Chemistry with Chelating Ligands toward Stable Aqueous Zn Anodes.

Changing the solvation sheath of hydrated Zn ions is an effective strategy to stabilize Zn anodes to obtain a practical aqueous Zn-ion battery. However, key points related to the rational design remain unclear including how the properties of the solvent molecules intrinsically regulate the solvated structure of the Zn ions. This study proposes the use of a stability constant (K), namely, the equilibrium constant of the complexation reaction, as a universal standard to make an accurate selection of ligands in the electrolyte to improve the anode stability. It is found that K greatly impacts the corrosion current density and nucleation overpotential. Following this, ethylene diamine tetraacetic acid with a superhigh K effectively suppresses Zn corrosion and induces uniform Zn-ion deposition. As a result, the anode has an excellent stability of over 3000 h. This work presents a general principle to stabilize anodes by regulating the solvation chemistry, guiding the development of novel electrolytes for sustainable aqueous batteries.

Crowning Metal Ions by Supramolecularization as a General Remedy toward a Dendrite-Free Alkali-Metal Battery.

Alkali metals have low potentials and high capacities, making them ideal anodes for next-generation batteries, but they suffer major problems, including dendrite growth and low Coulombic efficiency (CE). Achieving uniform metal deposition and having a reliable solid electrolyte interphase (SEI) are the basic requirements for overcoming these problems. Here, a general remedy is reported for various alkali-metal anodes by the supramolecularization of alkali-metal cations with crown ethers that follows a size-matching rule. The positively charged supramolecular complex provides electrostatic shielding layers to regulate metal deposition and suppress dendrite formation. More promisingly, it reforms electric double layers and drives the production of organic-dominated SEIs with improved flexibility that can accommodate large volume changes. The high flexibility of SEIs during metal deposition and dissolution reduces the amount of dead metal and improves CE and cycling stability. Specifically, a 200% excess Li-based full cell has a capacity retention of ≈100% after 100 cycles. This crown-like supramolecularization strategy is a new chemistry that may be used for the production of dendrite-free metal-anode-based batteries not limited to the cases with alkali metal. It is also expected as a practical technology to improve the uniformity of coatings produced in the electrodeposition industry.

Reversible electrochemical oxidation of sulfur in ionic liquid for high-voltage Al-S batteries.

Sulfur is an important electrode material in metal-sulfur batteries. It is usually coupled with metal anodes and undergoes electrochemical reduction to form metal sulfides. Herein, we demonstrate, for the first time, the reversible sulfur oxidation process in AlCl3/carbamide ionic liquid, where sulfur is electrochemically oxidized by AlCl4- to form AlSCl7. The sulfur oxidation is: 1) highly reversible with an efficiency of ~94%; and 2) workable within a wide range of high potentials. As a result, the Al-S battery based on sulfur oxidation can be cycled steadily around ~1.8 V, which is the highest operation voltage in Al-S batteries. The study of sulfur oxidation process benefits the understanding of sulfur chemistry and provides a valuable inspiration for the design of other high-voltage metal-sulfur batteries, not limited to Al-S configurations.