Integrated Actuation and Sensing: Toward Intelligent Soft Robots.

Soft robotics has received substantial attention due to its remarkable deformability, making it well-suited for a wide range of applications in complex environments, such as medicine, rescue operations, and exploration. Within this domain, the interaction of actuation and sensing is of utmost importance for controlling the movements and functions of soft robots. Nonetheless, current research predominantly focuses on isolated actuation and sensing capabilities, often neglecting the critical integration of these 2 domains to achieve intelligent functionality. In this review, we present a comprehensive survey of fundamental actuation strategies and multimodal actuation while also delving into advancements in proprioceptive and haptic sensing and their fusion. We emphasize the importance of integrating actuation and sensing in soft robotics, presenting 3 integration methodologies, namely, sensor surface integration, sensor internal integration, and closed-loop system integration based on sensor feedback. Furthermore, we highlight the challenges in the field and suggest compelling directions for future research. Through this comprehensive synthesis, we aim to stimulate further curiosity among researchers and contribute to the development of genuinely intelligent soft robots.

Untethered Small-Scale Machines for Microrobotic Manipulation: From Individual and Multiple to Collective Machines.

Untethered small-scale machines (USSMs) that can actively adjust their motion, deformation, and collective states in response to external stimuli have gained enormous interest in various manipulation, sensing, and biomedical applications. Because they can be efficiently operated in confined and tortuous environments, USSMs are capable of conducting wireless microrobotic manipulation tasks that tethered machines find hard to achieve. Over the past decade of development, significant research progress has been achieved in designing USSM-based manipulation strategies, which are enabled by investigating machine-object, machine-environment, and machine-machine interactions. This review summarizes the latest developments in USSMs for microrobotic manipulation by utilizing individual machines, coordinating multiple machines, and inducing collective behaviors. Providing recent studies and relevant applications in microrobotic and biomedical areas, we also discuss the challenges and future perspectives facing USSMs-based intelligent manipulation systems to achieve manipulation in complex environments with imaging-guided processes and increasing autonomy levels.

3D spray-coated gradient profile ceramic membranes enables improved filtration performance in aerobic submerged membrane bioreactor.

Rational design of cross-sectional microstructure in ceramic membranes has shown to improve membrane filtration efficacy without affecting rejection performance. In this work, we adopted 3D spray-coating technique to generate multi-layered membrane layers on macro-porous flat-sheet ceramic supports. The thickness of each layer was controlled by spray-coating cycles, and a gradient membrane layer was rationalized by successively coating three ceramic slurries containing alumina powders of gradually refined particle sizes, followed by co-sintering. Gradient membrane layers on both sides of the various sized flat-sheet ceramic supports were fabricated. Compared to the non-gradient counterpart, the gradient membranes showed both higher pure water flux (at the same TMP) and lower membrane resistance, which clearly evidenced the benefits of gradient profile in the membrane layer. Further, their performance in aerobic membrane bioreactors (AeMBR) was comparably studied for the first time. The treatment performance was not significantly affected by the types of membranes used, while the gradient membrane showed better filtration performance (i.e., a slower rise in TMP). Although the fouling mechanisms were revealed to be similar, the fouling layer in the gradient membrane was composed of a higher percentage of smaller foulants compared to that of the non-gradient counterpart. The observed differences were closely correlated to the larger internal pore structure in the gradient membrane. The present work provides a feasible 3D spray-coating technique for the fabrication of gradient flat-sheet ceramic membranes, and clarifies the benefits in AeMBR for domestic wastewater treatment.

Integrated Porous Cu Host Induced High-Stable Bidirectional Li Plating/Stripping Behavior for Practical Li Metal Batteries.

The double-sided electrodes with active materials are widely used for commercial lithium (Li) ion batteries with a higher energy density. Accordingly, developing an anode current collector that can accommodate the stable and homogeneous Li plating/stripping on both sides will be highly desired for practical Li metal batteries (LMBs). Herein, an integrated bidirectional porous Cu (IBP-Cu) film with a through-pore structure is fabricated as Li metal hosts using the powder sintering method. The resultant IBP-Cu current collector with tunable pore volume and size exhibits high mechanical flexibility and stability. The bidirectional and through-pore structure enables the IBP-Cu host to achieve homogeneous Li deposition and effectively suppresses the dendritic Li growth. Impressively, the as-fabricated Li/IBP-Cu anode exhibits a remarkable capacity of up to 7.0 mAh cm-2 for deep plating/stripping, outstanding rate performance, and ultralong cycling ability with high Coulombic efficiency of ≈100% for 1000 cycles. More practicably, a designed pouch cell coupled with one Li/IBP-Cu anode and two LiFePO4 cathodes exhibits a highly elevated energy density (≈187.5%) compared with a pouch cell with one anode and one cathode. Such design of a bidirectional porous Cu current collector with stable Li plating/stripping behaviors suggests its promising practical applications for next-generation Li metal batteries.

Efficient Hydrogen Evolution of Oxidized Ni-N3 Defective Sites for Alkaline Freshwater and Seawater Electrolysis.

For mass production of high-purity hydrogen fuel by electrochemical water splitting, seawater electrolysis is an attractive alternative to the traditional freshwater electrolysis due to the abundance and low cost of seawater in nature. However, the undesirable chlorine ion oxidation reactions occurring simultaneously with seawater electrolysis greatly hinder the overall performance of seawater electrolysis. To tackle this problem, electrocatalysts of high activity and selectivity with purposely modulated coordination and an alkaline environment are urgently required. Herein, it is demonstrated that atomically dispersed Ni with triple nitrogen coordination (Ni-N3 ) can achieve efficient hydrogen evolution reaction (HER) performance in alkaline media. The atomically dispersed Ni electrocatalysts exhibit overpotentials as low as 102 and 139 mV at 10 mA cm-2 in alkaline freshwater and seawater electrolytes, respectively, which compare favorably with those previously reported. They also deliver large current densities beyond 200 mA cm-2 at lower overpotentials than Pt/C, as well as show negligible current attenuation over 14 h. The X-ray absorption fine structure (XAFS) experimental analysis and density functional theory (DFT) calculations verify that the Ni-N3 coordination, which exhibits a lower coordination number than Ni-N4 , facilitates water dissociation and hydrogen adsorption, and hence enhances the HER activity.

Water treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives.

In recent years, many studies have been conducted on using different filter media in bioretention systems for stormwater runoff treatment. This critical review paper provides a comprehensive review on the current state of water treatment residual (WTR), a recycled material that can be used as bioretention filter media for removals of key stormwater runoff pollutants (especially phosphorus) and future perspectives with innovative modification on WTR applied for pathogen removal from stormwater runoff. This review paper comprised (i) a brief summary of the reported WTR characteristics, (ii) a thorough evaluation of WTR performance on major pollutants removal from stormwater runoff (iii) a discussion on phosphorus removal mechanisms by WTR applied in the stormwater runoff treatment, and (iv) a review of the future perspectives of WTR for pathogen removal and other potential practical application in the field of stormwater treatment. As outlined in this review, WTR in stormwater runoff treatment has yet to be fully explored. The possible enhancements, especially metal surface modification on WTR are reviewed to bring about the widespread use of WTR in stormwater reuse practices.

Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff.

Extensive studies have been conducted on bioretention filter media applied in best management practices for stormwater runoff treatment. To date, more reported studies are focused on pollutants elimination such as suspended solids and nutrients. There has been limited research on pathogen removal from stormwater runoff. More focused studies on pathogen removal are therefore required if the intended stormwater is harvested for indirect potable use. In this study, water treatment residuals (WTR), a recycled biofilter media was surface-modified with metals to assess its potential for E. coli removal from stormwater runoff. To achieve this goal, four types of modified WTRs, prepared using iron, copper, platinum, and silver as antibacterial agents, were tested in parallel batch tests. After the cost-effectiveness evaluation among the four modified WTRs for bacterial removal, Fe2O3- and CuO-WTRs were shortlisted for further mechanism and stability studies. Stable antibacterial performances (E. coli log removal of 0.58 ±â€¯0.04 and 0.90 ±â€¯0.04, respectively) were achieved using the Fe2O3- and CuO-WTRs under intermittent synthetic and natural stormwater runoff conditions. No significant metal leaching was observed over prolonged continuous treatment. The experimental results showed the bio-adsorption onto the surface modified Fe2O3- and CuO-WTR was a key mechanism for E. coli removal followed by E. coli inactivation at solid-liquid interface caused by the antibacterial effect of metal coatings (where CuO was reported to have higher biotoxicity than Fe2O3). These findings clearly suggested the potential of CuO-modified WTR for pathogen removal in stormwater treatment practices.

Twinned Tungsten Carbonitride Nanocrystals Boost Hydrogen Evolution Activity and Stability.

Synergistic integration of two active metal-based compounds can lead to much higher electrocatalytic activity than either of the two individually, due to the interfacial effects. Herein, a proof-of-concept strategy is creatively developed for the successful fabrication of twinned tungsten carbonitride (WCN) nanocrystals, where W2 C and WN are chemically bonded at the molecule level. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy analyses demonstrate that the intergrowth of W2 C and WN in the WCN nanocrystals produces abundant N-W-C interfaces, leading to a significant enhancement in catalytic activity and stability for hydrogen evolution reaction (HER). Indeed, it shows 14.2 times higher and 140 mV lower in the respective turn-over frequency (TOF) and overpotential at 10 mA cm-2 compared to W2 C alone. To complement the experimental observation, the theoretical calculations demonstrate that the WCN endows more favorable hydrogen evolution reaction than the single W2 C or WN crystals due to abundant interfaces, beneficial electronic states, lower work function, and more active W sites at the N-W-C interfaces.

Heterogeneous ZIF-L membranes with improved hydrophilicity and anti-bacterial adhesion for potential application in water treatment.

Although different metal-organic framework (MOF) membranes have been widely studied for gas separation, their application for water treatment is still in its infancy. MOF membranes with improved hydrophilicity and stability are particularly essential for water/wastewater treatment. Herein, we have successfully developed heterogeneous membranes (Zn/Co-ZIF-L) composed of vertically standing leaf-like crystals of Zn-ZIF-L grown in situ onto porous ceramic supports, followed by the subsequent heterogeneous growth of Co-ZIF-L. The heterogeneous membranes show improved hydrophilicity (WCA = 13.6 ± 1.6°) and enhanced anti-bacterial adhesion. Significantly, they simultaneously deliver a relative high water flux and much improved anti-bacterial adhesion when compared with the homogeneous membranes (Co-ZIF-L and Zn-ZIF-L). The improvements are attributed to the intrinsic hydrophilic nature of Co-ZIF-L, their epitaxial growth onto Zn-ZIF-L as well as the increased surface roughness. The success of constructing a heterogeneous MOF structure shows an effective strategy to achieve the hydrophilic MOF membranes with considerably enhanced stability for water treatment.

Atomic engineering of high-density isolated Co atoms on graphene with proximal-atom controlled reaction selectivity.

Controllable synthesis of single atom catalysts (SACs) with high loading remains challenging due to the aggregation tendency of metal atoms as the surface coverage increases. Here we report the synthesis of graphene supported cobalt SACs (Co1/G) with a tuneable high loading by atomic layer deposition. Ozone treatment of the graphene support not only eliminates the undesirable ligands of the pre-deposited metal precursors, but also regenerates active sites for the precise tuning of the density of Co atoms. The Co1/G SACs also demonstrate exceptional activity and high selectivity for the hydrogenation of nitroarenes to produce azoxy aromatic compounds, attributable to the formation of a coordinatively unsaturated and positively charged catalytically active center (Co-O-C) arising from the proximal-atom induced partial depletion of the 3d Co orbitals. Our findings pave the way for the precise engineering of the metal loading in a variety of SACs for superior catalytic activities.

Correction: Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries.

Correction for 'Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries' by Zhiyang Lyu et al., Chem. Soc. Rev., 2017, DOI: 10.1039/c7cs00255f.

Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries.

Aprotic Li-O2 batteries represent promising alternative devices for electrical energy storage owing to their extremely high energy densities. Upon discharge, insulating solid Li2O2 forms on cathode surfaces, which is usually governed by two growth models, namely the solution model and the surface model. These Li2O2 growth models can largely determine the battery performances such as the discharge capacity, round-trip efficiency and cycling stability. Understanding the Li2O2 formation mechanism and controlling its growth are essential to fully realize the technological potential of Li-O2 batteries. In this review, we overview the recent advances in understanding the electrochemical and chemical processes that occur during the Li2O2 formation. In the beginning, the oxygen reduction mechanisms, the identification of O2-/LiO2 intermediates, and their influence on the Li2O2 morphology have been discussed. The effects of the discharge current density and potential on the Li2O2 growth model have been subsequently reviewed. Special focus is then given to the prominent strategies, including the electrolyte-mediated strategy and the cathode-catalyst-tailoring strategy, for controlling the Li2O2 growth pathways. Finally, we conclude by discussing the profound implications of controlling Li2O2 formation for further development in Li-O2 batteries.

Water-Catalyzed Oxidation of Few-Layer Black Phosphorous in a Dark Environment.

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices.

Synthesis of porous CoMoO4 nanorods as a bifunctional cathode catalyst for a Li-O2 battery and superior anode for a Li-ion battery.

We report the synthesis of porous CoMoO4 nanorods and their applications in lithium oxygen (Li-O2) and lithium ion (Li-ion) batteries. The unique porous structures of CoMoO4 nanorods can promote the permeation of electrolyte and benefit the transport of lithium ion. When employed as the cathode catalyst for a Li-O2 battery, CoMoO4 nanorods deliver an improved discharge capacity (4680 mA h g-1), lower charge potential and better cycle stability (41 cycles at 500 mA h g-1 capacity limit) compared with the bare carbon. When employed as an anode in Li-ion batteries, CoMoO4 nanorods can retain a capacity of 603 mA h g-1 after 300 cycles (400 mA g-1) and exhibit excellent rate capability.

Monodispersed Ru Nanoparticles Functionalized Graphene Nanosheets as Efficient Cathode Catalysts for O2-Assisted Li-CO2 Battery.

In Li-CO2 battery, due to the highly insulating nature of the discharge product of Li2CO3, the battery needs to be charged at a high charge overpotential, leading to severe cathode and electrolyte instability and hence poor battery cycle performance. Developing efficient cathode catalysts to effectively reduce the charge overpotential represents one of key challenges to realize practical Li-CO2 batteries. Here, we report the use of monodispersed Ru nanoparticles functionalized graphene nanosheets as cathode catalysts in Li-CO2 battery to significantly lower the charge overpotential for the electrochemical decomposition of Li2CO3. In our battery, a low charge voltage of 4.02 V, a high Coulomb efficiency of 89.2%, and a good cycle stability (67 cycles at a 500 mA h/g limited capacity) are achieved. It is also found that O2 plays an essential role in the discharge process of the rechargeable Li-CO2 battery. Under the pure CO2 environment, Li-CO2 battery exhibits negligible discharge capacity; however, after introducing 2% O2 (volume ratio) into CO2, the O2-assisted Li-CO2 battery can deliver a high capacity of 4742 mA h/g. Through an in situ quantitative differential electrochemical mass spectrometry investigation, the final discharge product Li2CO3 is proposed to form via the reaction 4Li+ + 2CO2 + O2 + 4e- → 2Li2CO3. Our results validate the essential role of O2 and can help deepen the understanding of the discharge and charge reaction mechanisms of the Li-CO2 battery.

Porous CuO nanotubes/graphene with sandwich architecture as high-performance anodes for lithium-ion batteries.

Constructing a porous conductive framework represents a promising strategy for designing high-performance anodes for Li-ion batteries. Here, porous CuO nanotubes/graphene with hierarchical architectures were fabricated by simple annealing of copper nanowires/graphene hybrids synthesized by a microwave-assisted process. In these nanoarchitectures, the embedded porous CuO nanotubes can prevent restacking of the graphene sheets, whereas graphene can increase the electrical conductivity of CuO. Moreover, these two components constitute a sandwich-like interlaced framework that favors ion diffusion, as well as promoting better electron transport. As a result, the as-prepared nanohybrid exhibits a high specific capacity of 725 mA h g-1 and a capacity retention of ∼81% after 250 cycles, as well as outstanding rate performance in comparison to those of bare CuO or a CuO-CNT (carbon nanotubes) hybrid.

Synthesis of hierarchical porous δ-MnO2 nanoboxes as an efficient catalyst for rechargeable Li-O2 batteries.

A rechargeable lithium-oxygen (Li-O2) battery with a remarkably high theoretical energy storage capacity has attracted enormous research attention. However, the poor oxygen reduction and oxygen evolution reaction (ORR and OER) activities in discharge and charge processes cause low energy efficiency, poor electrolyte stability and short cycle life. This requires the development of efficient cathode catalysts to dramatically improve the Li-O2 battery performances. MnO2-based materials are recognized as efficient and low-cost catalysts for a Li-O2 battery cathode. Here, we report a controllable approach to synthesize hierarchical porous δ-MnO2 nanoboxes by using Prussian blue analogues as the precursors. The obtained products possess hierarchical pore size and an extremely large surface area (249.3 m(2) g(-1)), which would favour oxygen transportation and provide more catalytically active sites to promote ORR and OER as the Li-O2 battery cathode. The battery shows enhanced discharge capacity (4368 mA h g(-1)@0.08 mA cm(-2)), reduced overpotential (270 mV), improved rate performance and excellent cycle stability (248 cycles@500 mA h g(-1) and 112 cycles@1000 mA h g(-1)), in comparison with the battery with a VX-72 carbon cathode. The superb performance of the hierarchical porous δ-MnO2 nanoboxes, together with a convenient fabrication method, presents an alternative to develop advanced cathode catalysts for the Li-O2 battery.

Hydrophilic Hierarchical Nitrogen-Doped Carbon Nanocages for Ultrahigh Supercapacitive Performance.

The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances. Further nitrogen doping greatly improves the hydrophilicity, which boosts the supercapacitive performances to an ultrahigh specific capacitance of up to 313 F g(-1) at 1 A g(-1).