NaBix/NaVyOz Hybrid Interfacial Layer Enables Stable and Dendrite-Free Sodium Anodes.

The challenges of sodium metal anodes, including formation of an unstable solid-electrolyte interphase (SEI) and uncontrolled growth of sodium dendrites during charge-discharge cycles, impact the stability and safety of sodium metal batteries. Motivated by the promising commercialization potential of sodium metal batteries, it becomes imperative to systematically explore innovative protective interlayers specifically tailored for sodium metal anodes. In this work, a NaBix/NaVyOz hybrid and porous interfacial layer on sodium anode is successfully fabricated via pretreating sodium with bismuth vanadate. The hybrid interlayer effectively combines the advantages of sodium vanadates and alloys, raising a synergistic effect in facilitating sodium deposition kinetics and inhibiting the growth of sodium dendrites. As a result, the modified sodium electrodes (BVO-Na) can stably cycle for 2000 h at 0.5 mA cm-2 with a fixed capacity of 1 mAh cm-2, and the BVO-Na||Na3V2(PO4)3 full cell sustains a high capacity of 94 mAh g-1 after 600 cycles at 5 C. This work demonstrates that constructing an artificial hybrid interlayer is a practical solution to obtain high performance anodes in sodium metal batteries.

Partial Exsolution Enables Superior Bifunctionality of Ir@SrIrO3 for Acidic Overall Water Splitting.

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal-support interaction for OER and HER. Notably, the Ir@SrIrO3-175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mA cm-2 for OER and 28 mV at 10 mA cm-2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3-175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER.

Nickel-Regulated Composite Cathode with Balanced Triple Conductivity for Proton-Conducting Solid Oxide Fuel Cells.

Proton-conducting solid oxide fuel cells (H-SOFCs) have the potential to be a promising technology for energy conversion and storage. To achieve high chemical compatibility and catalytic activity, nickel-doped barium ferrate with triple conducting ability is developed as cathodes for H-SOFCs, presenting an impressive electrochemical performance at intermediate temperatures. The cell performance with the optimized BaCe0.26 Ni0.1 Fe0.64 O3 -δ (BCNF10) composite cathode reaches an outstanding performance of 1.04 W cm-2 at 600 °C. The high electrocatalytic capacity of the nickel-doped barium ferrate cathode can be attributed to its significant proton conductivity which is confirmed through hydrogen permeation experiments. Density functional theory (DFT) calculations are further conducted to reveal that the presence of nickel can enhance processes of hydration formation and proton migration, leading to improve proton conductivity and electro-catalytic activity.

Unique Proton Transportation Pathway in a Robust Inorganic Coordination Polymer Leading to Intrinsically High and Sustainable Anhydrous Proton Conductivity.

Although comprehensive progress has been made in the area of coordination polymer (CP)/metal-organic framework (MOF)-based proton-conducting materials over the past decade, searching for a CP/MOF with stable, intrinsic, high anhydrous proton conductivity that can be directly used as a practical electrolyte in an intermediate-temperature proton-exchange membrane fuel cell assembly for durable power generation remains a substantial challenge. Here, we introduce a new proton-conducting CP, (NH4)3[Zr(H2/3PO4)3] (ZrP), which consists of one-dimensional zirconium phosphate anionic chains and fully ordered charge-balancing NH4+ cations. X-ray crystallography, neutron powder diffraction, and variable-temperature solid-state NMR spectroscopy suggest that protons are disordered within an inherent hydrogen-bonded infinite chain of acid-base pairs (N-H···O-P), leading to a stable anhydrous proton conductivity of 1.45 × 10-3 S·cm-1 at 180 °C, one of the highest values among reported intermediate-temperature proton-conducting materials. First-principles and quantum molecular dynamics simulations were used to directly visualize the unique proton transport pathway involving very efficient proton exchange between NH4+ and phosphate pairs, which is distinct from the common guest encapsulation/dehydration/superprotonic transition mechanisms. ZrP as the electrolyte was further assembled into a H2/O2 fuel cell, which showed a record-high electrical power density of 12 mW·cm-2 at 180 °C among reported cells assembled from crystalline solid electrolytes, as well as a direct methanol fuel cell for the first time to demonstrate real applications. These cells were tested for over 15 h without notable power loss.

A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells.

Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5 + δ (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800 °C, the layered PBFM showed high electrical conductivity of 59.2 S cm(-1) in 5% H2 and peak power densities of 1.72 and 0.54 W cm(-2) using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0 A cm(-2). To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode.

Unravelling the Proton Conduction Mechanism from Room Temperature to 553 K in a 3D Inorganic Coordination Framework.

The preparation of proton-conducting materials that are functional and stable at intermediate temperatures (393-573 K) is a focal point of fuel cell development. The purely inorganic material, HNd(IO3)4, which possesses a dense 3D framework structure, can reach a maximum of 4.6 × 10(-4) S·cm(-1) at 353 K and 95% relative humidity and exhibit a high conductivity of 8.0 × 10(-5) S·cm(-1) from 373 to 553 K under the flow of wet N2. HNd(IO3)4 exhibits a variety of improvements including high thermal stability, low solubility in water, and resistance to reducing atmosphere. The proton conductivity in such a wide temperature range originates from the intrinsic liberated protons in the structure and the resulting 1D hydrogen-bonding network confirmed by bond valence sum calculation and solid-state NMR analysis. Moreover, two different activation energies are observed in different temperature regions (0.23 eV below 373 K and 0.026 eV from 373 to 553 K), indicating that two types of proton motion are responsible for proton diffusion, as further domenstrated by temperature-dependent open-circuit voltage hysteresis in a tested fuel cell assembly as well as variable-temperature and double quantum filtered solid-state NMR measurements.