Regulating Li Nucleation and Growth Heterogeneities via Near-Surface Lithium-Ion Irrigation for Stable Anode-Less Lithium Metal Batteries.

The inhomogeneous nucleation and growth of Li dendrite combined with the spontaneous side reactions with the electrolytes dramatically challenge the stability and safety of Li metal anode (LMA). Despite tremendous endeavors, current success relies on the use of significant excess of Li to compensate the loss of active Li during cycling. Herein, a near-surface Li+ irrigation strategy is developed to regulate the inhomogeneous Li deposition behavior and suppress the consequent side reactions under limited Li excess condition. The conformal polypyrrole (PPy) coating layer on Cu surface via oxidative chemical vapor deposition technique can induce the migration of Li+ to the interregional space between PPy and Cu, creating a near-surface Li+-rich region to smooth diffusion of ion flux and uniform the deposition. Moreover, as evidenced by multiscale characterizations including synchrotron high-energy X-ray diffraction scanning, a robust N-rich solid-electrolyte interface (SEI) is formed on the PPy skeleton to effectively suppress the undesired SEI formation/dissolution process. Strikingly, stable Li metal cycling performance under a high areal capacity of 10 mAh cm-2 at 2.0 mA cm-2 with merely 0.5 × Li excess is achieved. The findings not only resolve the long-standing poor LMA stability/safety issues, but also deepen the mechanism understanding of Li deposition process.

Suppressing Universal Cathode Crossover in High-Energy Lithium Metal Batteries via a Versatile Interlayer Design.

The universal cathode crossover such as chemical and oxygen has been significantly overlooked in lithium metal batteries using high-energy cathodes which leads to severe capacity degradation and raises serious safety concerns. Herein, a versatile and thin (≈25 µm) interlayer composed of multifunctional active sites was developed to simultaneously regulate the Li deposition process and suppress the cathode crossover. The as-induced dual-gradient solid-electrolyte interphase combined with abundant lithiophilic sites enable stable Li stripping/plating process even under high current density of 10 mA cm-2 . Moreover, X-ray photoelectron spectroscopy and synchrotron X-ray experiments revealed that N-rich framework and CoZn dual active sites can effectively mitigate the undesired cathode crossover, hence significantly minimizing Li corrosion. Therefore, assembled lithium metal cells using various high-energy cathode materials including LiNi0.7 Mn0.2 Co0.1 O2 , Li1.2 Co0.1 Mn0.55 Ni0.15 O2 , and sulfur demonstrate significantly improved cycling stability with high cathode loading.

Two-Dimensional Cobalt Sulfide/Iron-Nitrogen-Carbon Holey Sheets with Improved Durability for Oxygen Electrocatalysis.

Transition-metal sulfide as a promising bifunctional oxygen electrocatalyst alternative to scarce platinum-group metals has attracted much attention, but it suffers activity loss over time owing to poor structural/compositional stability during catalysis. Herein, we report a self-template method for preparing a two-dimensional cobalt sulfide holey sheet superstructure with hierarchical porosity followed by the encapsulation of thin iron-nitrogen-carbon as a protective layer. The iron-nitrogen-carbon layer to some degree precludes the phase transition of cobalt sulfide underneath and preserves the structural integrity during catalysis, therefore rendering an exceptional durability in terms of no obvious activity loss after 10,000 cycles of the accelerated durability test. It also noticeably enhances the intrinsic activity of cobalt sulfide and does not influence its exposure into the electrolyte, resulting in showing an extraordinary electrochemical performance in terms of a potential difference of 0.69 V for the overall oxygen redox. A rechargeable zinc-air battery assembled by a cobalt sulfide/iron-nitrogen-carbon air cathode delivers approximately 4.2 times higher power density than that without an iron-nitrogen-carbon layer and stably operates for 300 h with a high voltaic efficiency. This work gives a facile and effective strategy for improving the long-term durability of transition-metal sulfide electrocatalysts.

Microstructure Engineering of Fe/Fe3C-Decorated Metal-Nitrogen-Carbon Mesoporous Nanospheres via a Self-Template Method for Enhancing Oxygen Reduction Activity.

We report a self-template and facile pyrolysis method to synthesize Fe/Fe3C-decorated metal-nitrogen-carbon mesoporous nanospheres, of which preserved plum-like and hollow structures can be simply engineered via controlling the thickness of the outermost polydopamine layer in the precursors. The preserved plum-like structure is demonstrated to show a large electrochemically active surface area and facilitate fast charge transfer, in comparison with the hollow one. The catalytic activities of metal-nitrogen-carbon and nitrogen-doped carbon active sites in the outer carbon layer toward oxygen reduction are improved under the activation of the encased Fe species. Hence, preserved plum-like structures exhibit excellent catalytic kinetics toward the oxygen reduction reaction in alkaline media. The mass activity of 21.0 mA mgcatalyst-1 at 0.9 V vs RHE is achieved and the half-wave potential is 50 mV more positive than that of the Pt/C catalyst with the same mass loading. Moreover, the outer carbon layer endows the tolerance of strong acidic and alkaline environments, resulting in good durability. Our study proposes a simple strategy for the rational design of novel transition metal carbide-based catalysts, making it a promising candidate for replacing platinum-group metal catalysts in low-temperature fuel cells.

Well-Ordered Oxygen-Deficient CoMoO4 and Fe2O3 Nanoplate Arrays on 3D Graphene Foam: Toward Flexible Asymmetric Supercapacitors with Enhanced Capacitive Properties.

In this work, we report the development of well-ordered hydrogenated CoMoO4 (H-CoMoO4) and hydrogenated Fe2O3 (H-Fe2O3) nanoplate arrays on 3D graphene foam (GF) and explore their practice application as binder-free electrodes in assembling flexible all-solid-state asymmetric supercapacitor (ASC) devices. Our results show that the monolithic 3D porous GF prepared by solution casting method using Ni foam template possesses large surface area, superior electrical conductivity, and sufficient surface functional groups, which not only facilitate in situ growth of CoMoO4 and Fe2O3 nanoplates but also contribute the double-layer capacitance of the resultant supercapacitor. The well-ordered pseudocapacitive metal oxide nanoplate arrays standing up on 3D GF scaffold can provide efficient space and shorten the length for electrolyte diffusion from the outer to the inner region of the electrode material for Faradaic energy storage. Furthermore, one of our major findings is that the introduction of oxygen vacancies in CoMoO4 and Fe2O3 nanoplates by hydrogenation treatment can increase their electronic conductivity as well as improve their donor density and surface properties, which gives rise to a substantially improved electrochemical performance. Benefiting from the synergistic contributions of different components in the nanohybrid electrode, the resultant flexible ASC device with GF/H-CoMoO4 as the positive electrode and GF/H-Fe2O3 as the negative electrode achieves a wide operation voltage of 1.5 V and a maximum volumetric specific capacitance of 3.6 F cm-3, which is two times larger than that of the Ni/GF/CoMoO4//Ni/GF/Fe2O3 device (1.8 F cm-3), and the rate capability is up to 70% as the current density increases from 2 to 200 mA cm-3. Moreover, the Ni/GF/H-CoMoO4//Ni/GF/H-Fe2O3 device also exhibits a high energy density of 1.13 mWh cm-3 and a high power density of 150 mW cm-3, good mechanical flexibility with the decrease in capacitance of less than 4% after being bent inward to different angles and inward to 90° 200 times, and good cycling stability of 93.1% capacitance retention after 5000 cycles.

Pd Nanoparticles Decorated N-Doped Graphene Quantum Dots@N-Doped Carbon Hollow Nanospheres with High Electrochemical Sensing Performance in Cancer Detection.

The development of carbon based hollow-structured nanospheres (HNSs) materials has stimulated growing interest due to their controllable structure, high specific surface area, large void space, enhanced mass transport, and good biocompatibility. The incorporation of functional nanomaterials into their core and/or shell opens new horizons in designing functionalized HNSs for a wider spectrum of promising applications. In this work, we report a new type of functionalized HNSs based on Pd nanoparticles (NPs) decorated double shell structured N-doped graphene quantum dots (NGQDs)@N-doped carbon (NC) HNSs, with ultrafine Pd NPs and "nanozyme" NGQDs as dual signal-amplifying nanoprobes, and explore their promising application as a highly efficient electrocatalyst in electrochemical sensing of a newly emerging biomarker, i.e., hydrogen peroxide (H2O2), for cancer detection. Due to the synergistic effect of the robust and conductive HNS supports and catalytically active Pd NPs and NGQD in facilitating electron transfer, the NGQD@NC@Pd HNS hybrid material exhibits high electrocatalytic activity toward the direct reduction of H2O2 and can promote the electrochemical reduction reaction of H2O2 at a favorable potential of 0 V, which effectively restrains the redox of most electroactive species in physiological samples and eliminates interference signals. The resultant electrochemical H2O2 biosensor based hybrid HNSs materials demonstrates attractive performance, including low detection limit down to nanomole level, short response time within 2 s, as well as high sensitivity, reproducibility, selectivity, and stability, and have been used in real-time tracking of trace amounts of H2O2 secreted from different living cancer cells in a normal state and treated with chemotherapy and radiotherapy.