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Most issues with Li–S batteries are caused by the slowness of the multielectron sulfur electrochemical reaction resulting in the loss of sulfur as soluble polysulfides to the electrolyte and the redox shuttling of polysulfides between the cathode and anode during battery charge and discharge. The acceleration of the polysulfide conversion reaction to their end products via electrocatalysis has the appeal of a root-cause solution. However, the polysulfide electrocatalysts developed to date have rarely considered polysulfide conversion as a multistep reaction and, as such, were not optimized to target specific steps in the overall S8 ↔ Li2S n ↔ Li2S conversion. The targeting approach is however beneficial, as it can be used to design multicatalyst systems to reduce as many rate-limiting steps in the overall catalysis as effectively possible. This article demonstrates the concept and implementation of stepwise electrocatalysis in polysulfide conversion, using Fe–N and Co–N co-doped carbons to selectively catalyze the long-chain polysulfide conversion (S8 ↔ Li2S4) and the short-chain polysulfide conversion reactions (Li2S4 ↔ Li2S), respectively. The two electrocatalysts were deployed in the sulfur cathode as a dual layer, using an ordered spatial separation to synergize their catalytic effects. A sulfur electrode designed as such could utilize ∼90% of the sulfur theoretical specific capacity and support a high areal capacity of ∼8.3 mAh cm–2 and a low electrolyte/sulfur ratio of 5 μL mg–1.

Developing low-cost and biodegradable piezoelectric nanogenerators is of great importance for a variety of applications, from harvesting low-grade mechanical energy to wearable sensors. Many of the most widely used piezoelectric materials, including lead zirconate titanate (PZT), suffer from serious drawbacks such as complicated synthesis, poor mechanical properties (e.g. brittleness) and toxic composition, limiting their development for biomedical applications and posing environmental problems for their disposal. Here, we report a lowcost, biodegradable, biocompatible and highly compressible piezoelectric nanogenerator based on a wood sponge obtained with a simple delignification process. Thanks to the enhanced compressibility of the wood sponge, our wood nanogenerator (15 × 15 × 14 mm 3 , longitudinal × radial × tangential) can generate an output voltage of up to 0.69 V, 85 times higher than that generated by native (untreated) wood, and it shows stable performance under repeated cyclic compression (≥600 cycles). Our approach suggests the importance of increased compressibility of bulk materials for improving their piezoelectric output. We demonstrate the versatility of our nanogenerator by showing its application both as a wearable movement monitoring system (made with a single wood sponge) and as a large-scale prototype with increased output (made with 30 wood sponges) able to power simple electronic devices (a LED light, a LCD screen). Moreover, we demonstrate the biodegradability of our wood sponge piezoelectric nanogenerator by studying its decomposition with cellulosedegrading fungi. Our results showcase the potential application of wood sponge as a sustainable energy source, as a wearable device for monitoring human motions, and its contribution to environmental sustainability by electronic waste reduction.

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Photoinduced oxygen vacancies (OVs) are widely investigated as a vital point defect in wide-band-gap semiconductors. Still, the formation mechanism of OVs remains unclear in various materials. To elucidate the formation mechanism of photoinduced OVs in bismuth oxychloride (BiOCl), we synthesized two surface hydroxyl discrete samples in light of the discovery of the significant variance of hydroxyl groups before and after UV light exposure. It is noted that OVs can be obtained easily after UV light irradiation in the sample with surface hydroxyl groups, while variable changes were observed in samples without surface hydroxyls. Density functional theory (DFT) calculations reveal that the binding energy of Bi-O is drastically influenced by surficial hydroxyl groups, which is intensely correlated to the formation of photoinduced OVs. Moreover, DFT calculations reveal that the adsorbed water molecules are energetically favored to dissociate into separate hydroxyl groups at the OV sites via proton transfer to a neighboring bridging oxygen atom, forming two bridging hydroxyl groups per initial oxygen vacancy. This result is consistent with the experimental observation that the disappearance of photoinduced OVs and the recovery of hydroxyl groups on the surface of BiOCl after exposed to a HO(g)-rich atmosphere, and finally enables the regeneration of BiOCl photocatalyst. Here, we introduce new insights that the evolution of photoinduced OVs is dependent on surface hydroxyl groups, which will lead to the regeneration of active sites in semiconductors. This work is useful for controllable designs of defective semiconductors for applications in photocatalysis and photovoltaics.

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Constructing heterointerfaces between metals and metal compounds is an attractive strategy for the fabrication of high performance electrocatalysts. However, realizing the high degree of fusion of two different metal components to form heterointerfaces remains a great challenge, since the different metal components tend to grow separately in most cases. Herein, by employing carboxyl-modified carbon nanotubes to stabilize different metal ions, the engineering of abundant Ni|MnO heterointerfaces is achieved in porous carbon nanofibers (Ni|MnO/CNF) during the electrospinning-calcination process. Remarkably, the resulting Ni|MnO/ CNF catalyst exhibits activities that are among the best reported for the catalysis of both the oxygen reduction and oxygen evolution reactions. Moreover, the catalyst also demonstrates high power density and long cycle life in Zn-air batteries. Its superior electrochemical properties are mainly ascribed to the synergy between the engineering of oxygen-deficient Ni|MnO heterointerfaces with a strong Ni/Mn alloying interaction and the 1D porous CNF support. This facile anchoring strategy for the initiation of bimetallic heterointerfaces creates appealing opportunities for the potential use of heteronanomaterials in practical sustainable energy applications.

The applicability of advanced composite materials with hierarchical structure that conjugate metal–organic frameworks (MOFs) with macroporous materials is commonly limited by their inferior mechanical properties. Here, a universal green synthesis method for the in situ growth of MOF nanocrystals within wood substrates is introduced. Nucleation sites for different types of MOFs are readily created by a sodium hydroxide treatment, which is demonstrated to be broadly applicable to different wood species. The resulting MOF/wood composite exhibits hierarchical porosity with 130 times larger specific surface area compared to native wood. Assessment of the CO2 adsorption capacity demonstrates the efficient utilization of the MOF loading along with similar adsorption ability to that of pure MOF. Compression and tensile tests reveal superior mechanical properties, which surpass those obtained for polymer substrates. The functionalization strategy offers a stable, sustainable, and scalable platform for the fabrication of multifunctional MOF/wood‐derived composites with potential applications in environmental‐ and energy‐related fields.