The lithium-air battery (LAB) is envisaged as an ultimate energy storage device because of its highest theoretical specific energy among all known batteries. However, parasitic reactions bring about vexing issues on the efficiency and longevity of the LAB, among which the formation and decomposition of lithium carbonate Li CO is of paramount importance. The discovery of Li CO as the main discharge product in carbonate-based electrolytes once brought researchers to "the end of the idyll" in the early 2010s. In the past few years, tremendous efforts have been made to understand the formation and decomposition mechanisms of Li CO , as well as to conceive novel chemical/material strategies to suppress the Li CO formation and to facilitate the Li CO decomposition. Moreover, the study on Li CO in LABs is opening up a new research field in energy technology. Considering the rapid development and innumerous emerging issues, it is timely to recapitulate the current understandings, define the ambiguities and the scientific gaps, and discuss topics of high priority for future research, which is the aim of this Minireview.

Smart construction of ultraflexible electrodes with superior gravimetric and volumetric capacities is still challenging yet significant for sodium ion batteries (SIBs) toward wearable electronic devices. Herein, a hybrid film made of hierarchical Fe1−xS‐filled porous carbon nanowires/reduced graphene oxide (Fe1−xS@PCNWs/rGO) is synthesized through a facile assembly and sulfuration strategy. The resultant hybrid paper exhibits high flexibility and structural stability. The multidimensional paper architecture possesses several advantages, including rendering an efficient electron/ion transport network, buffering the volume expansion of Fe1−xS nanoparticles, mitigating the dissolution of polysulfides, and enabling superior kinetics toward efficient sodium storage. When evaluated as a self‐supporting anode for SIBs, the Fe1−xS@PCNWs/rGO paper electrode exhibits remarkable reversible capacities of 573–89 mAh g−1 over 100 consecutive cycles at 0.1 A g−1 with areal mass loadings of 0.9–11.2 mg cm−2 and high volumetric capacities of 424–180 mAh cm−3 in the current density range of 0.2–5 A g−1. More competitively, a SIB based on this flexible Fe1−xS@PCNWs/rGO anode demonstrates outstanding electrochemical properties, thus highlighting its enormous potential in versatile flexible and wearable applications.

Despite numerous advanced imaging and sterilization techniques available nowadays, the sensitive in vivo diagnosis and complete elimination of drug-resistant bacterial infections remain big challenges. Here we report a strategy to design activatable theranostic nanoprobes against methicillin-resistant Staphylococcus aureus (MRSA) infections. This probe is based on silica nanoparticles coated with vancomycin-modified polyelectrolyte-cypate complexes (SiO-Cy-Van), which is activated by an interesting phenomenon of bacteria-responsive dissociation of the polyelectrolyte from silica nanoparticles. Due to the aggregation of hydrophobic cypate fluorophores on silica nanoparticles to induce ground-state quenching, the SiO-Cy-Van nanoprobes are nonfluorescent in aqueous environments. We demonstrate that MRSA can effectively pull out the vancomycin-modified polyelectrolyte-cypate complexes from silica nanoparticles and draw them onto their own surface, changing the state of cypate from off (aggregation) to on (disaggregation) and leading to in vitro MRSA-activated near-infrared fluorescence (NIRF) and photothermal elimination involving bacterial cell wall and membrane disruption. In vivo experiments show that this de novo-designed nanoprobe can selectively enable rapid (4 h postinjection) NIRF imaging with high sensitivity (10 colony-forming units) and efficient photothermal therapy (PTT) of MRSA infections in mice. Remarkably, the SiO-Cy-Van nanoprobes can also afford a long-term tracking (16 days) of the development of MRSA infections, allowing real-time estimation of bacterial load in infected tissues and further providing a possible way to monitor the efficacy of antimicrobial treatment. The strategy of bacteria-activated polyelectrolyte dissociation from nanoparticles proposed in this work could also be used as a general method for the design and fabrication of bacteria-responsive functional nanomaterials that offer possibilities to combat drug-resistant bacterial infections.

Graphitic carbon nitride (g-C 3 N 4 ) has recently emerged as a promising metal-free photocatalytic material for the conversion of solar energy into chemical energy under visible-light irradiation. Unfortunately, the photocatalytic activity of g-C 3 N 4 is still unsatisfactory due to the serious recombination of photogenerated electron−hole pairs. Here, we develop a strategy to construct a type of g-C 3 N 4 -based composite photocatalyst (C 3 N 4 / CBV 2+ ), a g-C 3 N 4 surface coupled with a viologen redox mediator (1,1′-bis(4-carboxylatobenzyl)-4,4′-bipyridinium dichloride, denoted as CBV 2+ ) through hydrogen bonds, for enhanced H 2 production from water under visible-light irradiation. The CBV 2+ molecules not only provide sites for metal particle formation but also act as an efficient electron transfer mediator to transfer the photoinduced electrons from g-C 3 N 4 to platinum nanoparticles (Pt NPs). The vectorial charge transfer results in an efficient spatial separation of electrons and holes in the C 3 N 4 /CBV 2+ composite photocatalyst and facilitates the photogenerated charge carriers for direct photocatalytic water splitting. When 1 wt % CBV 2+ is introduced, the hydrogen production rate of C 3 N 4 / CBV 2+ dramatically increases up to 41.57 μmol h −1 , exceeding 85 times the rate over unmodified g-C 3 N 4 (only 0.49 μmol h −1 ). It is noted that a negligible loss of photocatalytic activity was observed over continuous irradiation up to 20 h, demonstrating its good stability. The combination of the two emerging functional materials represents a simple but economical and powerful approach for highly effective photocatalytic hydrogen production under visible light irradiation. This study opens a window to rationally develop cost-acceptable materials for more efficient solar energy conversion applications. KEYWORDS: g-C 3 N 4 /viologen, hydrogen bond, visible-light photocatalysis, hydrogen evolution, charge separation efficiency

A trace-O2-assisted aprotic Li-CO2 battery represents a promising approach for CO2 recycling. However, cathode passivation and large overpotential are frequently observed for current Li-CO2 batteries because of the insolubility and nonconductivity of the discharge product of lithium carbonate (Li2CO3). Toward maximizing the energy capabilities of the Li-CO2 electrochemistry, it is crucially important to have a fundamental understanding of the Li2CO3 formation mechanism in Li-CO2 batteries. In this report, the discharge reaction of a trace-O2-assisted Li-CO2 battery has been interrogated with in situ surface-enhanced Raman spectroscopy. It was found that in high-donor-number (DN) solvents Li2CO3 formation proceeds primarily via an “electrochemical solution route”, with peroxodicarbonate (C2O6 2–) as the key intermediate, whereas in low-DN solvents Li2CO3 forms via a chemical reaction of Li2O2 and CO2 on the cathode surface, namely, a “chemical surface route”. It is notable that during discharge the trace-O2 acts as a “pseudo-catalyst” to activate CO2 in high-DN solvents but not in low-DN solvents. The mechanistic study presented here will assist us in tailor-designing better electrolyte systems and enable more energetic electrochemistry operation far away from the poison of Li2CO3.

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Cobalt-rich cobalt phosphide catalysts on cobalt foils as integrated bifunctional electrodes have been developed and display outstanding performances towards overall water splitting.

Cost-efficiency utilization of value-added, biomass-based carbon materials is essential for versatile electrochemical energy-related applications. Herein, we smartly devised a universal and ecofriendly FeCl3-activating methodology for scalable, high-yield fabrication of biomass-derived hierarchical porous N-doped carbons for supercapacitors. The underlying FeCl3-involved activating mechanism was reasonably put forward. The mushroom-derived porous N-doped carbon, as a typical FeCl3-activating example, was endowed with a large surface area of ∼1143.6 m2 g–1, high-fraction (∼66.3%) mesopores, high-content (∼3.1 at. %) N doping, and good wettability and exhibited even better electrochemical behaviors when compared to those activated by KOH and/or without activation, thanks to its innately structural/componental/surfacial superiorities. The resultant carbon electrode with a high loading of 5 mg cm–2 displayed competitive gravimetric/volumetric capacitances of ∼307.4 F g–1 (∼212.1 F cm–3) at 1 A g–1 in 1 M H2SO4, much better than those in KOH, mainly owing to extra pseudocapacitance. Moreover, the assembled symmetric devices yielded high energy densities of ∼6.6 (1 M H2SO4) and ∼62.6 Wh kg–1 (1 M (TEA)­BF4/PC) at a high rate of 1.5 kW kg–1, and ultralong cycling performance. More significantly, the FeCl3-involved synthetic protocol is highly promising and general for other biomass-derived porous carbon materials toward advanced supercapacitors.