Advanced Engineering for Cathode in Lithium–Oxygen Batteries: Flexible 3D Hierarchical Porous Architecture Design and Its Functional Modification

Modern technology constantly requires smaller, more efficient lithium–oxygen batteries (LOBs). To meet this need, a chemical vapor deposition (CVD) method is used to create an innovative cathode design with both a hierarchical porous nanostructure and a 3D flexible macroscopical morphology. This method employs architectural optimization to further improve cathodic ORR and OER performance via heteroatom doping, surface-sprouted carbon nanofibers (CNFs) grafting, and boundary exposing. The cathode consists of a 3D hierarchical porous graphene foam (PGF), along with RuO₂ nanoparticles impregnated and nitrogen doped CNFs (RuO₂@NCNFs), where the PGF serves as a structural support and cathodic current collector, and the RuO₂@NCNFs work as a superior bi-functional catalyst. The cathode delivers an outstanding discharge capacity of 8440 mAh g_cathode⁻¹ while maintaining a recharge plateau at ≈4.0 V, and can cycle for over 700 rounds without obvious degeneration under a fixed capacity. Notably, this free-standing cathode can be directly used in LOBs without the need for additional substrates or current collectors. Therefore, the current densities and capacities herein are calculated based on the total weight of the cathodes. These results demonstrate the RuO₂@NCNFs-PGF cathode's remarkable potential for LOB applications, and this rational cathodic structure may be extended to other highly efficient catalyst applications.     

Phase-Modulation of Iron/Nickel Phosphides Nanocrystals “Armored” with Porous P-Doped Carbon and Anchored on P-Doped Graphene Nanohybrids for Enhanced Overall Water Splitting

Transition metal phosphides (TMPs) nanostructures have emerged as important electroactive materials for energy storage and conversion. Nonetheless, the phase modulation of iron/nickel phosphides nanocrystals or related nanohybrids remains challenging, and their electrocatalytic overall water splitting (OWS) performances are not fully investigated. Here, the phase-controlled synthesis of iron/nickel phosphides nanocrystals “armored” with porous P-doped carbon (PC) and anchored on P-doped graphene (PG) nanohybrids, including FeP–Fe₂P@PC/PG, FeP–(Ni_xFe_1-x)₂P@PC/PG, (Ni_xFe_1-x)₂P@PC/PG, and Ni₂P@PC/PG, are realized by thermal conversion of predesigned supramolecular gels under Ar/H₂ atmosphere and tuning Fe/Ni ratio in gel precursors. Thanks to phase-modulation-induced increase of available catalytic active sites and optimization of surface/interface electronic structures, the resultant pure-phase (Ni_xFe_1-x)₂P@PC/PG exhibits the highest electrocatalytic activity for both hydrogen and oxygen evolution in alkaline media. Remarkably, using it as a bifunctional catalyst, the fabricated (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG electrolyzer needs exceptional low cell voltage (1.45 V) to reach 10 mA cm⁻² water-splitting current, outperforming its mixed phase and monometallic phosphides counterparts and recently reported bifunctional catalysts based devices, and Pt/C || IrO₂ electrolyzer. Also, such (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG device manifests outstanding durability for OWS. This work may shed light on optimizing TMPs nanostructures by combining phase-modulation and heteroatoms-doped carbon double-confinement strategies, and accelerate their applications in OWS or other renewable energy options.     

Regulation of Cathode Mass and Charge Transfer by Structural 3D Engineering for Protonic Ceramic Fuel Cell at 400 °C

Lowering the operating temperature (ideally below 400 °C) for solid oxide fuel cell (SOFC) technology deployment has been an important transition that introduces the benefit of reduced operational costs and system durability. However, the key technical issue limiting the transition is the sluggish cathodic performance, namely the oxygen reduction reaction (ORR) rate of the conventional sponge-like cathode dramatically drops as the temperature reduces. In this paper, 3D engineering of a cathode is conducted on a protonic ceramic fuel cell to obtain an enhanced ORR between 400 and 600 °C. Compared with a cell using a conventional sponge-like cathode, 3D engineering improves the cathode ORR by 41% at 400 °C with a peak power density of 0.410 W cm⁻². A phase field simulation is applied to assist the engineering by understanding the competition between the cathode mass and charge transfer with different cathode porosities. The results show that structural engineering of existing well-developed cathodes is a simple and effective method to promote cathode ORR for low temperature SOFC by regulating the mass and charge transfer.     

Synergistic Manipulation of Zn2+ Ion Flux and Nucleation Induction Effect Enabled by 3D Hollow SiO2/TiO2/Carbon Fiber for Long-Lifespan and Dendrite-Free Zn–Metal Composite Anodes

Aqueous rechargeable zinc–metal batteries are a promising candidate for next-generation energy storage devices due to their intrinsic high capacity, low cost, and high safety. However, uncontrollable dendrite formation is a serious problem, resulting in limited lifespan and poor coulombic efficiency of zinc–metal anodes. To address these issues, a 3D porous hollow fiber scaffold with well-dispersed TiO₂, SiO₂, and carbon is used as superzincophilic host materials for zinc anodes. The amorphous TiO₂ and SiO₂ allow for controllable nucleation and deposition of metal Zn inside the porous hollow fiber even at ultrahigh current densities. Furthermore, the as-fabricated interconnected conductive hollow SiO₂ and TiO₂ fiber (HSTF) possess high porosity, high conductivity, and fast ion transport. Meanwhile, the HSTF exhibits remarkable mechanical strength to sustain massive Zn loading during repeated cycles of plating/stripping. The HSTF with interconnected conductive network can build a uniform electric field, redistributing the Zn²⁺ ion flux and resulting in smooth and stable Zn deposition. As a result, in symmetrical cells, the Zn@HSTF electrode delivers a long cycle life of over 2000 cycles at 20 mA cm⁻² with low overpotential (≈160 mV). The excellent cycling lifespan and low polarization are also realized in Zn@HSTF//MnO₂ full cells.     

Nerve-Fiber-Inspired Construction of 3D Graphene “Tracks” Supported by Wood Fibers for Multifunctional Biocomposite with Metal-Level Thermal Conductivity

Given the rapid developments in modern electronics, there is an urgent need for polymer composites with excellent heat-dissipating capabilities to address the cooling problem of these devices. However, designing a highly thermally conductive polymer composite that can outperform metals and ceramics while also exhibiting high processability and low cost remains a challenge. Herein, inspired by the fibrous pathway of human nervous system, natural wood fibers (WFs) are used as the template and coated with graphene nanoplates (GNPs) via a simple electrostatic self-assembly approach. Subsequent hot-pressing process yields “core-sheath” microstructured fibers, wherein the GNPs are compactly contacted face to face and arranged along the surfaces of the fibrous WF “cores”. This WF@G biocomposite consists of highly efficient 3D fibrous “tracks” for heat transmission, resulting in an extremely high thermal conductivity of 134 W (m K)⁻¹, which is at par with those of many metals. It also exhibits several other desirable properties and functionalities, including high mechanical strength and excellent flame resistance as well as remarkable electromagnetic shielding and Joule heating performances, which has significant potential for use as a functional thermal management material (TMM). Hence, this study describes a simple yet scalable manufacturing technique for the development of advanced metal-level biomass-based TMMs.