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.

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.

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.

Transfer learning-based channel estimation in orthogonal frequency division multiplexing systems using data-nulling superimposed pilots.

Data-nulling superimposed pilot (DNSP) effectively alleviates the superimposed interference of superimposed training (ST)-based channel estimation (CE) in orthogonal frequency division multiplexing (OFDM) systems, while facing the challenges of the estimation accuracy and computational complexity. By developing the promising solutions of deep learning (DL) in the physical layer of wireless communication, we fuse the DNSP and DL to tackle these challenges in this paper. Nevertheless, due to the changes of wireless scenarios, the model mismatch of DL leads to the performance degradation of CE, and thus faces the issue of network retraining. To address this issue, a lightweight transfer learning (TL) network is further proposed for the DL-based DNSP scheme, and thus structures a TL-based CE in OFDM systems. Specifically, based on the linear receiver, the least squares estimation is first employed to extract the initial features of CE. With the extracted features, we develop a convolutional neural network (CNN) to fuse the solutions of DL-based CE and the CE of DNSP. Finally, a lightweight TL network is constructed to address the model mismatch. To this end, a novel CE network for the DNSP scheme in OFDM systems is structured, which improves its estimation accuracy and alleviates the model mismatch. The experimental results show that in all signal-to-noise-ratio (SNR) regions, the proposed method achieves lower normalized mean squared error (NMSE) than the existing DNSP schemes with minimum mean square error (MMSE)-based CE. For example, when the SNR is 0 decibel (dB), the proposed scheme achieves similar NMSE as that of the MMSE-based CE scheme at 20 dB, thereby significantly improving the estimation accuracy of CE. In addition, relative to the existing schemes, the improvement of the proposed scheme presents its robustness against the impacts of parameter variations.

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.

Ultrathin carbon nanotube-DNA hybrid membrane formation by simple physical adsorption onto a thin alumina substrate.

Ultrathin carbon nanotube membranes can be prepared on alumina substrates by a facile immersion-adsorption approach, which involves two steps, the first step DNA wrapping and the second step uniform adsorption of the DNA-wrapped nanotubes onto porous alumina. In this approach, DNA wrapping imparts a hydrophilic nature to the carbon nanotubes, which enhances the interaction between the nanotubes and hydrophilic porous alumina and results in the self-assembly formation of ultrathin nanotube membranes with well-controlled thickness, biocompatibility, conductivity and optical properties.

Critical Role of Surface Defects in the Controllable Deposition of Li2S on Graphene: From Molecule to Crystallite.

Uncontrollable electrochemical deposition of Li2S has negative impacts on the electrochemical performance of lithium-sulfur batteries, but the relationship between the deposition and the surface defects is rarely reported. Herein, ab initio molecular dynamics (AIMD) and density functional theory (DFT) approaches are used to study the Li2S deposition behaviors on pristine and defected graphene substrates, including pyridinic N (PDN) doped and single vacancy (SV), as well as the interfacial characteristics, in that such defects could improve the polarity of the graphene material, which plays a vital role in the cathode. The result shows that due to the constraint of molecular vibration, Li2S molecules tend to form stable adsorption with PDN atoms and SV defects, followed by the nucleation of Li2S clusters on these sites. Moreover, the clusters are more likely to grow near these sites following a spherical pattern, while a lamellar pattern is favorable on pristine graphene substrates. It is also discovered that PDN atoms and SV defects provide atomic-level pathways for the electronic transfer within the Li2S-electrode interface, further improving the electrochemical performance of the Li-S battery. It is found for the first time that surface defects also have strong impacts on the deposition pattern of Li2S and provide electronic pathways simultaneously. Our work demonstrated the interior relationship between the surface defects in carbon substrates and the stability of Li2S precipitates, which is of high significance to understand the electrochemical kinetics and design Li-S battery with long cycle life.

Room-temperature reduction of NO2 in a Li-NO2 battery: a proof of concept.

Although considerable effort has been devoted to purifying nitrogen oxides (NOx), it is still challenging to effectively reduce NOx at room temperature and ambient pressure without catalysts. In this study, as a proof-of-concept, we have for the first time demonstrated the room-temperature reduction of nitrogen dioxide (NO2) using a rechargeable lithium-nitrogen dioxide (Li-NO2) battery. The battery shows a capacity of 884 mAh g-1 at 50 mA g-1 (an actual energy density of 666 Wh kg-1) and a promising electrochemical Faraday efficiency (FE) of 67%. The unique properties of Li-NO2 rechargeable batteries not only provide a way to reduce and recycle NO2 but also highlight the potential of oxidative air pollutants as energy sources for next-generation electrochemical energy storage (EES) systems.

Catalytic Effects in Lithium-Sulfur Batteries: Promoted Sulfur Transformation and Reduced Shuttle Effect.

Lithium-sulfur (Li-S) battery has emerged as one of the most promising next-generation energy-storage systems. However, the shuttle effect greatly reduces the battery cycle life and sulfur utilization, which is great deterrent to its practical use. This paper reviews the tremendous efforts that are made to find a remedy for this problem, mostly through physical or chemical confinement of the lithium polysulfides (LiPSs). Intrinsically, this "confinement" has a relatively limited effect on improving the battery performance because in most cases, the LiPSs are "passively" blocked and cannot be reused. Thus, this strategy becomes less effective with a high sulfur loading and ultralong cycling. A more "positive" method that not only traps but also increases the subsequent conversion of LiPSs back to lithium sulfides is urgently needed to fundamentally solve the shuttle effect. Here, recent advances on catalytic effects in increasing the rate of conversion of soluble long-chain LiPSs to insoluble short-chain Li2S2/Li2S, and vice versa, are reviewed, and the roles of noble metals, metal oxides, metal sulfides, metal nitrides, and some metal-free materials in this process are highlighted. Challenges and potential solutions for the design of catalytic cathodes and interlayers in Li-S battery are discussed in detail.