Flexible capacitive pressure sensor based on interdigital electrodes with porous microneedle arrays for physiological signal monitoring

Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stability have hindered their large-scale commercial application.Herein,aflexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays(MNAs)is pro-posed.The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3.Due to its porous and interdigital structure,the maximum sensitivity(0.07 kPa-1)of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor,and it was much greater than that of aflat pressure sensor without a porous MNA structure.Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sen-sor.In addition,the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure.Most importantly,it was found that the sensor could accurately monitor the motion of afinger,wrist joint,arm,face,abdomen,eye,and Adam’s apple.Furthermore,preliminary semantic recognition was achieved by monitoring the movement of the Adam’s apple.Finally,multiple pressure sensors were integrated into a 33 array to detect a spatial pressure distribu-×tion.Compared to the sensors reported in previous works,the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.

Capacitive energy storage from single pore to porous electrode identified by frequency response analysis

Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.

Electro-enhanced adsorption of As(V)by activated carbon in three-dimensional electrode reactor

This study focused on As(V)removal by electrosorption in a self-made three-dimensional electrode reactor,in which granular activated carbon(GAC)was used as the particle electrode.Under the optimal conditions,the removal efficiency of As(V)was 84%,and its residual concentration in solution was 0.08 mg/L.From kinetic investigation,the rate determining steps of the entire process may involve more than two processes:membrane diffusion,material diffusion and physical/chemical adsorption processes.During the desorption process,As(V)can be desorbed from GAC,and the GAC was able to electro-adsorb As(V)again after desorption,which means that the electrode has good cycling performance.

Electrochemical degradation of acidified reed pulp black liquor with three-dimensional electrode reactor

The electrochemical degradation of reed pulp black liquor containing lignin pretreated by acidification method was investigated using a three-dimensional electrode reactor. Using activated carbon as particle electrode, the effects of p H value, reaction temperature, electrolysis time and current on residual concentration of total organic carbon(TOC) were discussed in detail. The optimal conditions were obtained: pH 2.5, influent flow rate of 200 mL/min, 25 °C, 300 mA and 2h of electrolysis time, and the removal efficiency of TOC maintains at 35.57 %. The results of the electrochemical method indicate that ·OH radicals are produced in activated carbon anode in the electrolysis process and then adsorbed on the activated carbon surface. Microcell consists of ·OH radicals and the absorbed lignin. With the microcell reaction, the lignin is degraded, while the anodic polarized curve illustrates that the lignin is obviously oxidized in the anode. The contributions of direct and indirect electrolyses to the TOC removal ratio are about 50%, respectively.

Electrochemical Degradation of o-Chloronitrobenzene by Three-dimensional Electrodes

Degradation of o-chloronitrobenzene wastewater was experimentally investigated at a three-dimensional electrode（TDE） with granular activated carbon as the particle electrode, graphite as the anode, and stainless steel plate as the cathode. The kinetic model of o-chloronitrobenzene degradation was studied, and the effects of pH, electrolysis time, particle electrode, electrolyte concentration, and initial concentration of the solution on degradation efficiency were investigated to determine the optimal operating conditions. The degradation of o-chloronitrobenzene by oxidation at the TDE was monitored by chemical oxygen demand（COD） measurements, UV-Vis absorption, and high performance liquid chromatography（HPLC）. COD degradation by electrochemical degradation followed pseudo-first order kinetics with respect to the concentration of o-chloronitrobenzene solutions. Optimal reaction conditions included 15 g of activated carbon as the particle electrode, 400 mg/L o-chloronitrobenzene solution containing 0.10 mol/L Na2SO4, pH=3, and 60 min of electrolysis. The UV-Vis absorption spectra and HPLC results illustrate that the benzene ring in o-chloronitrobenzene was rapidly broken down to form aliphatic substances through electrochemical degradation. COD degradation was approximately 98.5% at optimal conditions.

Preparation and Electrochemical Characteristics of Three-dimensional Manganese Oxide Micro-supercapacitor Electrode

In order to increase the electrode surface area and enhance the charge storage capacity, we study the micro electro mechanical system technology to fabricate three-dimensional high aspect ratio micro-electrode structure based on glass. The anodic constant potential method is employed to deposit manganese oxide as electroactive substances on the micro-electrode surface. Cyclic voltammetry and constant current charge-discharge method are both used to prepare electrode electrochemical performance testing, with a two-dimensional electrode without structure for comparison. Experimental results show that three-dimensional elec- trode structure can effectively enhance the charge storage capacity. At 1.0 mA/cm2 charge- discharge density, the three-dimensional electrode shows a capacitance of 17.88 mF/cm2, seven times higher than the two-dimensional electrode.

Three-dimensional vertical ZnO transistors with suspended top electrodes fabricated by focused ion beam technology

Three-dimensional(3D)vertical architecture transistors represent an important technological pursuit,which have distinct advantages in device integration density,operation speed,and power consumption.However,the fabrication processes of such 3D devices are complex,especially in the interconnection of electrodes.In this paper,we present a novel method which combines suspended electrodes and focused ion beam(FIB)technology to greatly simplify the electrodes interconnection in 3D devices.Based on this method,we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al_(2)O_(3) gate-oxide both grown by atomic layer deposition.Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires,which avoid cumbersome steps in the traditional 3D structure fabrication technology.Both single pillar and arrays devices show well behaved transfer characteristics with an Ion/Ioff current ratio greater than 106 and a low threshold voltage around 0 V.The ON-current of the 2×2 pillars vertical channel transistor was 1.2μA at the gate voltage of 3 V and drain voltage of 2 V,which can be also improved by increasing the number of pillars.Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.

Preparation and performance of hierarchically porous carbons as oxygen electrodes for lithium oxygen batteries

The hierarchically porous carbons （HPCs） were prepared by sol-gel selassembly technology in different surfactant concentrations and were used as the potential electrode for lithium oxygen batteries. The physical and electrochemical properties of the as-prepared HPCs were investigated by filed emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM）, nitrogen adsorption-desorption isotherm and galvanostatic charge/discharge. The results indicate that all of the HPCs mainly possess mesoporous structure with nearly similar pore size distribution. Using the HPCs as the electrode, a high discharge capacity for lithium oxygen battery can be achieved, and the discharge capacity increases with the specific surface area. Especially, the HPCs-3 oxygen electrode with CTAB concentration of 0.27 mol/L exhibits good capacity retention through controlling discharge depth to 800 mA·h/g and the highest discharge capacity of 2050 mA·h/g at a rate of 0.1 mA/cm2.

Training image analysis for three-dimensional reconstruction of porous media

In order to obtain a better sandstone three-dimensional （3D） reconstruction result which is more similar to the original sample, an algorithm based on stationarity for a two-dimensional （2D） training image is proposed. The second-order statistics based on texture features are analyzed to evaluate the scale stationarity of the training image. The multiple-point statistics of the training image are applied to obtain the multiple-point statistics stationarity estimation by the multi-point density function. The results show that the reconstructed 3D structures are closer to reality when the training image has better scale stationarity and multiple-point statistics stationarity by the indications of local percolation probability and two-point probability. Moreover, training images with higher multiple-point statistics stationarity and lower scale stationarity are likely to obtain closer results to the real 3D structure, and vice versa. Thus, stationarity analysis of the training image has far-reaching significance in choosing a better 2D thin section image for the 3D reconstruction of porous media. Especially, high-order statistics perform better than low-order statistics.

Electrochemical discharging performance of 3D porous magnesium electrode in organic electrolyte

A novel type of porous magnesium electrode with a stable 3D copper foam as current collectors for the organic magnesium-air battery was prepared by both amperostatic and pulsed electrodeposition of magnesium on copper foam substrates in an electrolyte of 1 mol/L EtMgBr/THF solution, respectively. Optimal parameters of the pulsed electrodeposition were obtained using a bending cathode at the right angle. The surface morphology of the porous electrode was investigated by SEM, and the discharging performance of the porous magnesium electrode was detected by the chronoamperometric measurement. The electrochemical stability of 3D copper foam current collectors was examined by cyclic voltammetry, SEM and ICP-OES analyses. The results show that the rate capability of the porous magnesium electrode with a stable 3D copper foam as a current collector is better than that of the planar magnesium electrode, and the rate capability of the porous magnesium electrode prepared by the pulsed electrodeposition is superior to that of the porous magnesium electrode prepared by the amperostatic electrodeposition. The 3D structure of copper foam current collectors of the porous magnesium electrode could keep stable during the discharging process.

Preparation of porous Mg electrode by electrodeposition

In order to obtain a porous Mg electrode with a stable skeleton, organic Mg fuel cell （OMFC）, the electrochemical behavior of Mg deposition on Cu and Ni metallic substrates in 1 mol/L EtMgBr/THF solution was investigated by SEM, EDS and electrochemical methods. The experimental results show that Mg can be electrodeposited on both substrates, as a continuous layer on a Cu substrate. Accordingly, an approach for producing a porous Mg electrode with a stable skeleton of OMFC was proposed by means of electrodeposition of Mg on a foamed Ni substrate with a layer of Cu pre-plating. The discharge performance of this porous Mg electrode of OMFC is superior to that of a planar Mg electrode.

Multiscale modeling of electrolytes in porous electrode:From equilibrium structure to non-equilibrium transport

Understanding the mechanisms and properties of various transport processes in the electrolyte,porous electrode,and at the interface between electrode and electrolyte plays a crucial role in guiding the improvement of electrolytes,materials and microstructures of electrode.Nanoscale equilibrium properties and nonequilibrium ion transport are substantially different to that in the bulk,which are difficult to observe from experiments directly.In this paper,we introduce equilibrium and no-equilibrium thermodynamics for electrolyte in porous electrodes or electrolyte-electrode interface.The equilibrium properties of electrical double layer(EDL)including the EDL structure and capacitance are discussed.In addition,classical non-equilibrium thermodynamic theory is introduced to help us understand the coupling effect of different transport processes.We also review the recent studies of nonequilibrium ion transport in porous electrode by molecular and continuum methods,among these methods,dynamic density functional theory(DDFT)shows tremendous potential as its high efficiency and high accuracy.Moreover,some opportunities for future development and application of the non-equilibrium thermodynamics in electrochemical system are prospected.

Functional porous carbon-based composite electrode materials for lithium secondary batteries

The synthetic routes of porous carbons and the applications of the functional porous carbon-based composite electrode materials for lithium secondary batteries are reviewed. The synthetic methods have made great breakthroughs to control the pore size and volume, wall thickness, surface area, and connectivity of porous carbons, which result in the development of functional porous carbon-based composite electrode materials. The effects of porous carbons on the electrochemical properties are further discussed. The porous carbons as ideal matrixes to incorporate active materials make a great improvement on the electrochemical properties because of high surface area and pore volume, excellent electronic conductivity, and strong adsorption capacity. Large numbers of the composite electrode materials have been used for the devices of electrochemical energy conversion and storage, such as lithium-ion batteries （LIBs）, Li-S batteries, and Li-O2 batteries. It is believed that functional porous carbon-based composite electrode materials will continuously contribute to the field of lithium secondary batteries.

Analytical modeling and simulation of porous electrodes: Li-ion distribution and diffusion-induced stress

A new model of porous electrodes based on the Gibbs free energy is developed, in which lithium-ion(Liion) diffusion, diffusion-induced stress(DIS), Butler–Volmer(BV) reaction kinetics, and size polydispersity of electrode particles are considered. The influence of BV reaction kinetics and concentration-dependent exchange current density(ECD) on concentration profile and DIS evolution are numerically investigated. BV reaction kinetics leads to a decrease in Li-ion concentration and DIS. In addition, concentrationdependent ECD results in a decrease in Li-ion concentration and an increase in DIS. Size polydispersity of electrode particles significantly affects the concentration profile and DIS.Optimal macroscopic state of charge(SOC) should consider the influence of the microscopic SOC values and mass fractions of differently sized particles.

Newly Design Porous/Sponge Red Phosphorus@Graphene and Highly Conductive Ni2P Electrode for Asymmetric Solid State Supercapacitive Device With Excellent Performance

Supercapacitors have attracted much attention in the field of electrochemical energy storage.However,material preparation,stability,performance as well as power density limit their applications in many fields.Herein,a sponge-like red phosphorus@graphene(rP@rGO)negative electrode and a Ni2P positive electrode were prepared using a simple one-step method.Both electrodes showed excellent performances(294 F g^−1 and 1526.6 F g^−1 for rP@rGO and Ni2P,respectively),which seem to be the highest among all rP@rGO-and Ni2P-based electrodes reported so far.The asymmetric solid-state supercapacitor was assembled by sandwiching a gel electrolyte-soaked cellulose paper between rP@rGO and Ni2P as the negative and positive electrodes.Compared to other asymmetric devices,the device,which attained a high operating window of up to 1.6 V,showed high energy and power density values of 41.66 and 1200 W kg−1,respectively.It also has an excellent cyclic stability up to 88%after various consecutive charge/discharge tests.Additionally,the device could power commercial light emitting diodes and fans for 30 s.So,the ease of the synthesis method and excellent performance of the prepared electrode materials mat have significant potential for energy storage applications.

Two-Phase Flow in Porous Electrodes of Proton Exchange Membrane Fuel Cell

Water management in porous electrodes bears significance due to its strong potential in determining the performance of proton exchange membrane fuel cell.In terms of porous electrodes,internal water distribution and removal process have extensively attracted attention in both experimental and numerical studies.However,the structural difference among the catalyst layer(CL),microporous layer(MPL),and gas diffusion layer(GDL)leads to significant challenges in studying the two-phase flow behavior.Given the different porosities and pore scales of the CL,MPL,and GDL,the model scales in simulating each component are inconsistent.This review emphasizes the numerical simulation related to porous electrodes in the water transport process and evaluates the effectiveness and weakness of the conventional methods used during the investigation.The limitations of existing models include the following:(i)The reconstruction of geometric models is difficult to achieve when using the real characteristics of the components;(ii)the computational domain size is limited due to massive computational loads in three-dimensional(3 D)simulations;(iii)numerical associations among 3 D models are lacking because of the separate studies for each component;(iv)the effects of vapor condensation and heat transfer on the two-phase flow are disregarded;(v)compressive deformation during assembly and vibration in road conditions should be considered in two-phase flow studies given the real operating conditions.Therefore,this review is aimed at critical research gaps which need further investigation.Insightful potential research directions are also suggested for future improvements.

Flexible heteroatom-doped porous carbon nanofiber cages for electrode scaffolds

Porous carbon nanofibers(PCNFs)with rich functionalities and high surface areas are important electrode scaffolds to load active materials,but increasing their pore volumes and strength simultaneously is a challenge.Here,we report a scalable method to fabricate B-F-N triply doped PCNF cages with high porosity of greater than 92.8%and small bending stiffness of 10 mN by electrospinning the mixed sol of poly(tetrafluoroethylene),poly(vinyl alcohol),boric acid,and carbon nanotubes(CNTs)followed by pyrolysis.The macromicro dual-phase separation creates well-controlled macropores(>60 nm)and meso-micropores with large pore volumes(0.55 cm3/g)on carbon nanofibers,while the interior CNTs can cushion the applied stress and render the PCNF films with superior flexibility.Fabricated symmetrical supercapacitors with the PCNF cages exhibit high gravimetric capacitance of 164 F/g at 20 mV/s and 92.5%capacity retention after 20000 cycles at 2 A/g.The reported approach allows the green synthesis of a new PCNF scaffold material with properties appealing for applications.

Preparation and Electrochemical Properties of Porous Platinum Electrode

Porous platinum electrodes were prepared by adding YSZ,as an active material,in platinum paste.Relationship between microstructure and electrochemical performance of O 2(g),Pt/YSZ electrode have been characterized by SEM and cyclic voltammetry.Results showed that the microstructure of platinum electrode is a significant impact on the cyclic voltammetry.With the increase of platinum electrode's porosity,the area of three-phase boundary of O 2(g) /Pt/YSZ was increased.The electrochemical reactivity was also enhanced.These were presented as the increase of current density and cathode voltage in cyclic voltammetry.

Three-dimensional consolidation deformation analysis of porous layered soft soils considering asymmetric effects

Long-term settlements for underground structures, such as tunnels and pipelines, are generally observed after the completion of construction in soft clay. The soil consolidation characteristic has great influences on the long-term deformation for underground structures. A three-dimensional consolidation analysis method under the asymmetric loads is developed for porous layered soil based on Biot's classical theory. Time-displacement effects can be fully considered in this work and the analytical solutions are obtained by the state space approach in the Cartesian coordinate. The Laplace and double Fourier integral transform are applied to the state variables in order to reduce the partial differential equations into algebraic differential equations and easily obtain the state space solution. Starting from the governing equations of saturated porous soil, the basic relationship of state space variables is established between the ground surface and the arbitrary depth in the integral transform domain. Based on the continuity conditions and boundary conditions of the multi-layered pore soil model, the multi-layered pore half-space solutions are obtained by means of the transfer matrix method and the inverse integral transforms. The accuracy of proposed method is demonstrated with existing classical solutions. The results indicate that the porous homogenous soils as well as the porous non-homogenous layered soils can be considered in this proposed method. When the consolidation time factor is 0.01, the value of immediate consolidation settlement coefficient calculated by the weighted homogenous solution is 27.4% bigger than the one calculated by the non-homogeneity solution. When the consolidation time factor is 0.05, the value of excess pore water pressure for the weighted homogenous solution is 27.2% bigger than the one for the non-homogeneity solution. It is shown that the material non-homogeneity has a great influence on the long-term settlements and the dissipation process of excess pore water pressure.

Self-templating synthesis of biomass-based porous carbon nanotubes for energy storage and catalytic degradation applications

Dwindling energy sources and a worsening environment are huge global problems,and biomass wastes are an under-exploited source of material for both energy and material generation.Herein,self-template decoction dregs of Ganoderma lucidum-derived porous carbon nanotubes(ST-DDLGCs)were synthesized via a facile and scalable strategy in response to these challenges.ST-DDLGCs exhibited a large surface area(1731.51 m^(2)g^(-1))and high pore volume(0.76 cm^(3)g^(-1)),due to the interlacing tubular structures of precursors and extra-hierarchical porous structures on tube walls.In the ST-DDLGC/PMS system,the degradation efficiency of capecitabine(CAP)reached~97.3%within 120 min.Moreover,ST-DDLGCs displayed high catalytic activity over a wide pH range of 3–9,and strong anti-interference to these typical and ubiquitous anions in wastewater and natural water bodies(i.e.,H_(2)PO_(4)^(-),NO_(3)^(-),Cl^(-) and HCO_(3)^(-)),in which a ^(1)O_(2)-dominated oxidation was identified and non-radical mechanisms were deduced.Additionally,ST-DDLGC-based coin-type symmetrical supercapacitors exhibited outstanding electrochemical performance,with specific capacitances of up to 328.1 F g^(-1)at 0.5 A g^(-1),and cycling stability of up to 98.6%after 10,000 cycles at a current density of 2 A g^(-1).The superior properties of ST-DDLGCs could be attributed to the unique porous tubular structure,which facilitated mass transfer and presented numerous active sites.The results highlight ST-DDLGCs as a potential candidate for constructing inexpensive and advanced environmentally functional materials and energy storage devices.