Ionic Layer Research Articles

(Invited) CdS/Ti-Si-O Composite Photoanode for Photoelectrochemical Hydrogen Generation

Advancements in clean energy drive socio-economic development and foster a sustainable future by restructuring energy systems and promoting low-carbon development. In this paper, we presented a comprehensive investigation on the design and performance characterization of CdS/Ti-Si-O composite photoanodes for photoelectrochemical (PEC) hydrogen generation. Silicon-doped TiO2 nanotube arrays were fabricated through anodization of Ti-5Si alloy, followed by the deposition of CdS using the SILAR (successive ionic layer adsorption and reaction) process, resulting in nanostructured Ti-Si-O photoanodes modified with CdS. The composite photoanodes were characterized in terms of their composition, microstructure, optical properties and photoelectrochemical hydrogen production performance. The composite photoanodes revealed a notable enhancement in PEC hydrogen generation properties with a photocurrent density of 7.86 mA/cm2，which was 19.15 times and 9.59 times to those of the undoped TiO2 photoanode and Ti-Si-O photoanode, respectively. The Si-doping mechanism of the photoanodes was elucidated through Density Functional Theory (DFT) calculations. The synergistic combination of Si-doping and CdS modification represents a novel and promising approach for the design of efficient nanostructured photoanodes.

Stabilized Nickel-Rich oxide cathode by the confining effect of Nb lattice anchoring and epitaxial shielding layer

Ni-rich LiNixCoyMn1−x−yO2 cathodes attract growing attention for high energy density but still face great challenges in terms of cyclic lifespan and thermal stability issues. The structural degradation is primarily caused by the increased oxygen vacancy and lattice oxygen loss, especially at high temperatures. Here, we develop an anchoring-confining strategy to rivet lattice oxygen and inhibit the formation and migration of oxygen vacancy by constructing LiNbO3 & LiF epitaxial layer and Nb5+ lattice doping within LiNi0.92Co0.055Mn0.025O2 (NCM92) cathode. The optimized NCM-FN material exhibits excellent stability with retenion of 93 % after 200 cycles at 1C supassing the pristine one (68.7 %), conspicuous high-temperature capacity retention rate (81.6 % vs. 49.5 %) and superior reversible capacity of 165 mAh/g at 5C. In particular, it even possessed superior thermal safety pushing thermal runaway temperature to 223.65 °C. In-situ X-ray diffraction (XRD) result indicates that Nb5+ lattice substitution coupled with LiNbO3 & LiF epitaxial layer alleviates the irreversibility of H2-H3 phase transition, thus stabilizing the layered structure. Furthermore, the LiNbO3 & LiF epitaxial layer, as both a physical shielding layer and ionic conductive layer, protects interface structural integrity and simultaneously promotes Li+ diffusion. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results demonstrate that the formation and propagation of oxygen vacancy within NCM-FN material is significantly inhibited. DFT calculation results reveal that Nb5+ introduction can increase the formation energy of oxygen vacancies and inhibit outward migration of active oxygen Oα- (α < 2) to stabilize layer structure by tuning the breaking energy barrier of nearby metal-O bonds. This work not only demonstrates the design of advanced Ni-rich layered cathodes but also underscores the importance of stabilized lattice oxygen for advanced Ni-rich cathodes.

Interface-modulated kinetic differentials in electron and hole transfer rates as a key design principle for redox photocatalysis by Sb2VO5/QD heterostructures.

The efficient conversion of solar energy to chemical energy represents a critical bottleneck to the energy transition. Photocatalytic splitting of water to generate solar fuels is a promising solution. Semiconductor quantum dots (QDs) are prime candidates for light-harvesting components of photocatalytic heterostructures, given their size-dependent photophysical properties and band-edge energies. A promising series of heterostructured photocatalysts interface QDs with transition-metal oxides which embed midgap electronic states derived from the stereochemically active electron lone pairs of p-block cations. Here, we examine the thermodynamic driving forces and dynamics of charge separation in Sb2VO5/CdSe QD heterostructures, wherein a high density of Sb 5s2-derived midgap states are prospective acceptors for photogenerated holes. Hard-x-ray valence band photoemission spectroscopy measurements of Sb2VO5/CdSe QD heterostructures were used to deduce thermodynamic driving forces for charge separation. Interfacial charge transfer dynamics in the heterostructures were examined as a function of the mode of interfacial connectivity, contrasting heterostructures with direct interfaces assembled by successive ion layer adsorption and reaction (SILAR) and interfaces comprising molecular bridges assembled by linker-assisted assembly (LAA). Transient absorption spectroscopy measurements indicate ultrafast (<2ps) electron and hole transfer in SILAR-derived heterostructures, whereas LAA-derived heterostructures show orders of magnitude differentials in the kinetics of hole (<100ps) and electron (∼1ns) transfer. The interface-modulated kinetic differentials in electron and hole transfer rates underpin the more effective charge separation, reduced charge recombination, and greater photocatalytic efficiency observed for the LAA-derived Sb2VO5/CdSe QD heterostructures.

Highly stable flexible ozone gas sensors using Mn3O4 nanoparticles-decorated IGZO thin films through the SILAR method

Metal or semiconductor nanoparticles (NPs) can enhance the device performance of gas sensors due to their high surface area and unique electronic properties. However, this method requires additional thermal bonding with high temperatures to secure the NPs, making it unsuitable for flexible substrates. In this study, we develop a room-temperature flexible ozone (O3) gas sensor using Mn3O4 NPs on an amorphous InGaZnO (a-IGZO) film. The Mn3O4 NPs are synthesized by a successive ionic layer adsorption and reaction (SILAR) method at low temperatures. The sensor with Mn3O4 NPs exhibits a gas response of 4.06 against 5 ppm O3 gas at room temperature, which is much higher than that of its pristine counterpart. It also shows excellent selectivity for O3 over toxic gases and maintains stability over 60 days, with reproducible folding even after 500 bending cycles. Thus, the combination of SILAR-synthesized Mn3O4 NPs and a-IGZO films provides an effective way to fabricate flexible O3 gas sensors.

Fabrication and characterization of ZnWO4/CoWO4 heterojunction for multispectral photodetection on flexible substrate

Flexible photodetectors hold significant interest across diverse applications, such as imaging, communication, healthcare, and environmental monitoring. This work reports a broad-band photodetector comprising Zinc tungstate (ZW) and Cobalt tungstate (CW) on a flexible paper substrate. CW thin film was fabricated by a facile successive ionic layer adsorption and reaction(SILAR) technique and the ZW nanoparticles, synthesised via simple co-precipitation method, were drop casted on it to form a heterojunction. Structural characterization of the materials was conducted using X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR), while scanning electron microscopy was employed for detailed morphology analysis. CW is a p type semiconductor with its bandgap of 2.6 eV, exhibits impressive sensitivity across both visible and infrared segments of the electromagnetic spectrum. In contrast, ZW which is n type contributes UV-responsive, attributes effectively broadening the overall spectral sensitivity from Ultraviolet (UV) to Infrared (IR) spectra within a single compact device. The photodetector demonstrates remarkable responsivity of 1.66 mA/W (UV), 24.58 mA/W (Visible), and 0.024 mA/W (IR) under respective light intensities of 0.6 mW/cm², 0.4 mW/cm², and 4.41 mW/cm. The detectivity metrics are equally impressive, measuring at 9.9×1010 Jones (UV), 5.01×1011 Jones (Visible), and 4.48×1010 Jones (IR). The successful combination of Zinc tungstate and Cobalt tungstate on a paper substrate represents an advancement in photodetector technology, offering enhanced sensitivity, extended spectral range, and the potential for seamless integration into wearable electronics and portable devices.

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study.

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.

Research Progress of Heavy-Metal-Free Quantum Dot Light-Emitting Diodes.

At present, heavy-metal-free quantum dot light-emitting diodes (QLEDs) have shown great potential as a research hotspot in the field of optoelectronic devices. This article reviews the research on heavy-metal-free quantum dot (QD) materials and light-emitting diode (LED) devices. In the first section, we discussed the hazards of heavy-metal-containing quantum dots (QDs), such as environmental pollution and human health risks. Next, the main representatives of heavy-metal-free QDs were introduced, such as InP, ZnE (E=S, Se and Te), CuInS2, Ag2S, and so on. In the next section, we discussed the synthesis methods of heavy-metal-free QDs, including the hot injection (HI) method, the heat up (HU) method, the cation exchange (CE) method, the successful ionic layer adsorption and reaction (SILAR) method, and so on. Finally, important progress in the development of heavy-metal-free QLEDs was summarized in three aspects (QD emitter layer, hole transport layer, and electron transport layer).

Formation of a potential barrier by a ZnSXSe1−X electron-blocking layer to improve the efficiency of CdSe0.3S0.7/CdSe quantum dot sensitized solar cells

We designed and fabricated multilayer quantum dots sensitized solar cells (QDSCs) with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnSXSe1−X, X = S/S + Se = 0, 0.7, 0.8, 0.9, and 1 photoelectrodes to achieve optimum power conversion efficiency (PCE). In the corresponding structure, incoming light is absorbed by the CdSe0.3S0.7 and CdSe quantum dots (QDs), while the ZnSXSe1−X QDs act as an electron blocking layer or passivation layer, forming an energy barrier that restricts electron mobility from the light absorbers to the polysulfide electrolyte. The beneficial effect of the alloyed ZnSXSe1−X layer is the adjustability of its nanoparticle size/bandgap energy proportional to variations in the concentration of anionic precursors X, according to optical results. The PCE value of the reference cell with the TiO2 NPs/CdSe0.3S0.7/CdSe photoanode is 4.15 %. Following the coating of ZnSe, ZnS0.7Se0.3, ZnS0.8Se0.2, ZnS0.9Se0.1, and ZnS QDs via two successive ionic layer adsorption and reaction (SILAR) cycles (2Sc) on the CdSe0.3S0.7/CdSe co-sensitized photoelectrode increasing stability and improving the PCE value to 4.9 %, 5.40 %, 5.70, 5.25 %, and 5.05 %, respectively. Next, by modifying the thickness of the champion cell's passivation layer, the QDSCs with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnS0.8Se0.2 (3Sc) photoelectrode exhibit maximum photovoltaic performance parameters of short circuit current density (JSC) = 26.25 mA/cm2, open circuit voltage (VOC) = 560 mV, fill factor (FF) = 0.42 % and PCE = 6.15 %. This improvement in performance is the result of decreased internal energy loss and recombination of charge carriers at the interface between the electrolyte and photoelectrode, which increases electron collection efficiency and electron injection efficiency in the visible region according to the external and internal quantum efficiency curves.

Amine-impregnated natural inorganic nanotubes via layer-by-layer electrostatically self-assembly approach for efficient CO2 adsorption

Developing cost-effective and high-performance solid amine adsorbents has considered as an important way to alleviate the greenhouse effect. How to precisely regulate its pore structure and surface interface characteristics, and how to cooperate to optimize the dynamic mass transfer and adsorption–desorption behavior of gas in the adsorbent are still challenging work. Herein, we demonstrated a facile and efficient approach to construct polyethyleneimine (PEI) impregnated halloysite nanotubes (HNTs) as an emerging nanocomposite for CO2 capture. Based on the natural electrostatic differences of inner and outer walls for HNTs, the hollow tubular structures of adsorbents were constructed by selective surface modification and layer-by-layer electrostatic self-assembly technology to improve the CO2 uptake capacity and cyclic stability, in which poly(sodium-p-styrene sulfonate) (PSS) and PEI were used as polyanionic and polycationic layer, respectively, to coat the inner walls of HNTs. The loading capacity of PSS-PEI composite ionic layers in HNTs and the influence of PSS polyanionic layer on PEI dispersion were specifically discussed according to the CO2 uptake capacity, adsorption heat, thermodynamics and kinetics of the adsorbents. The optimal PEI20-0.5PHNTs adsorbent exhibited a higher CO2 uptake of 0.87 mmol/g at 80 °C in the flow of 40 vol% N2/60 vol% CO2 than that of PEI20-HNTs, owing to the high amine efficiency due to the uniform dispersion of PEI in the electrostatic composite ionic layers. Furthermore, PEI20-0.5PHNTs reached 75 % of the maximum adsorption capacity at the 5th min of the adsorption process and released the most heat during adsorption at − 18.28 kJ/mol due to the presence of electrostatic composite ionic layers. PEI20-0.5PHNTs showed excellent cyclic stability with a slight loss of 7.4 %. The electrostatic self-assembled adsorbent obtained by layer-by-layer loading of PSS and PEI based on the unique surface charge characteristics of HNTs is an inspiration for the synthesis of cost-effective solid amine adsorbents for practical CO2 capture and separation.

Unconventionally microspheric quasi-solid electrolyte interface approach for durable and highly reactive phosphorus for lithium-ion storage

Solid electrolyte interface (SEI) film is the most important separation layer between nonaqueous electrolytes and anodes to protect anode from corrosion and maintain continuous ionic diffusion tunnels. However, SEI film, especially for high-capacity anode materials, is still confined to continuous and stable ionic conductive layer despite the conventional SEI film is intrinsically poor to resist against the drastic volumetric changes of active centers. Herein, an unconventional spheric quasi-SEI film is thus strategically configured on cost-effective red phosphorus electrode materials by moderate phosphorylation combined with pore-forming process. Microstructure adjustment from solid microspheres structure to hollowed core–shell spheres is visibly taken place on this amazing spheric quasi-SEI film during the stabilization. Benefiting from the highly activated surface with weakened PP bond strength and the strengthened binding force between phosphorus and binders, the optimized phosphorus anode presents an outstanding long-term durability with a high discharge capacity of 1126.4 mAh/g over 400 cycles at 200 mA g−1 even at a high phosphorus load ratio of 70 wt%. This revolutionary configuration of quasi-SEI film provides high-capacity anode materials subject to large volumetric changes an unconventional approach from dependence on conductive framework/matrix.

Modified successive ionic layer adsorption and reaction for interconnected bismuth vanadate nanograins: Highly active visible light harvesting photoanodes

A modified successive ionic layer adsorption and reaction (SILAR) method is developed for depositing interconnected bismuth vanadate (BiVO4) nanoparticles with improved visible light harvesting activity. Facile control of preparative parameters like deposition cycles, anionic precursor, pH and deposition temperature significantly altered BiVO4 surface morphology. BiVO4 thin films prepared with Na3VO4 anionic precursor show dispersed nanoparticles type morphology and that deposited with NaVO3 precursor displays 3D interconnected nanoparticles morphology. The BiVO4 photoanodes with 3D interconnected nanoparticles morphology exhibits an excellent photocurrent density of 5.19 mA cm−2 at 1.23 V vs. RHE with superior photostability and improved applied bias photon to current efficiency (ABPE) (1.50 %) compared to dispersed nanostructured BiVO4 photoanodes. The excellent photoelectrochemical (PEC) characteristics of BiVO4 photoanodes with 3D interconnected nanoparticle morphology can be ascribed to porous morphology, optimum thickness, narrow band gap energy and favorable electronic band structure for water splitting. The current study illustrates the usefulness of the modified SILAR approach for depositing 3D interconnected BiVO4 nanoparticle morphology in a single step that is superior and efficient to previously reported multistep processes.

Coating effect of metal organic complex (Co-DTPMP) layer on enhancing PEC water oxidation performance of BiVO4 photoanode

Photoelectrochemical (PEC) water splitting is a promising method for transforming solar energy into clean and sustainable energy. However, PEC is severely limited, and they cannot achieve the predicted photocurrent density owing to the severe photochemical deterioration of the electrode and the recombination of photogenerated carriers. In this study, BiVO4/Co-diethylenetriamine Penta (methylene phosphonic acid) (BVO/Co-DTPMP) co-catalyst was successfully prepared as a nanoporous photoanode. Diethylenetriamine Penta (methylene phosphonic acid) was crosslinked with Co ions and coated on the BiVO4 surface by successive ionic layer adsorption and reaction (SILAR) to reduce fast recombination, which correlated with the BiVO4 photoanode. Various characterization and PEC measurements were conducted, revealing that the co-catalyst thin layer enhanced the charge separation and electrons transfer which significantly affected on the PEC performance of BiVO4, and the current density by BVO/Co-DTPMP was 4 mA cm−2 at 1.23 V vs. RHE. Furthermore, the co-catalyst exhibited improved charge transport and long-term stability.

Half-metal Mn2GeI2 monolayer with high Curie temperature and large perpendicular magnetic anisotropy

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials with high Curie temperatures (Tc), large perpendicular magnetic anisotropy (PMA), and large spin polarization are desirable for atomically thin spintronic devices. Herein, we propose a 2D intrinsic FM material Mn2GeI2 monolayer with thermodynamical stability and outstanding FM properties using first-principles calculations. Our calculations show that Mn2GeI2 monolayer is a half-metal with a spin gap of 1.76 eV, which ensures 100% spin polarization ratio at the Fermi level. Importantly, Mn2GeI2 monolayer has a large PMA energy of 2.90 meV and a high Tc of 648 K, ideal for practical applications at room temperature. Further in-depth investigation of microscopic coupling in the Mn2GeI2 monolayer reveals that the robust ferromagnetism mainly resulted from the synthetic effect of Ruderman–Kittel–Kasuya–Yosida exchange interaction between the Mn ion layers and superexchange interaction within the Mn ion layers. Our results give insights into the structure and electronic and magnetic properties of Mn2GeI2 monolayer and provide a promising candidate for 2D spintronic devices.

Ion‐Impregnated Intermediate Layer for Enhancing Triboelectric Nanogenerator Performance

AbstractThe triboelectric nanogenerator (TENG) is gaining recognition as a highly promising, eco‐friendly self‐powered device for the growth of the Internet of Things (IoT). To improve the performance of TENGs, diverse materials are employed as interlayers. However, challenges related to cost and stability persist. Herein, a strategy that incorporates ion‐containing electrolyte polymers as interlayers is presented. This approach effectively mitigates charge decay and maximizes TENG efficiency by leveraging the high charge capacitance of the ionic electric double layer (iEDL). The incorporation of iEDL into TENG results in an approximate tenfold increase in current density (10–92 mA m−2) and a 13‐fold increase in power density (2–26 W m−2). The robust energy generation capabilities of iEDL‐TENG enable the operation of 100 LED lights and the charging of a 470 µF capacitor. Furthermore, the demonstrated device exhibits significant stability across 10,000 operational cycles and effectively maintains its performance when subjected to external physical forces such as blade‐induced cuts, penetrating wounds, and severe crumpling.

Enhancing photocatalytic performance of BiOI/TiO2 NTs nanocomposites through SILAR optimization for methylene blue degradation

BiOI nano-leaves were deposited on to TiO2 nanotubes (NTs) using the Successive Ionic Layer Adsorption and Reaction (SILAR) technique, which was developed using the electrochemical anodization method. Various SILAR cycle numbers (three, five, and seven cycles) were employed in the experiment. The as-prepared nanocomposites (NCs) were characterized by several technique, the morphology of the elaborated NCs samples was examined using a S − 4800 field emission scanning electron microscope (SEM), the Reflectance and diffuse reflectivity of the NCs samples were measured by a Shimadzu UV-3100S spectrophotometer in the spectral range [300 –1200 nm] and the XRD diffraction was used to identify the crystalline structure of the processed BiOI/TiO2 NTs nanocomposites. A diffractometer with a Cu Kα anode (λ = 0.1542 nm) operating at 40 kV and 30 mA was used. The as-prepared NCs, specifically BiOI/TiO2 NTs, were designed for the photocatalytic degradation of methylene Blue (MB). X-ray diffraction analysis revealed the formation of the TiO2 anatase phase and polycrystalline BiOI films in all processed NCs. UV/Vis measurements indicated a shift in the nanocomposite’s active region from UV to visible light. The highest absorption and the lowest bandgap energy (Eg value, ∼2 eV) were observed in the NCs with 5 BiOI cycles. The photocurrent density reached 27 μA cm−2, approximately three times higher than the photocurrent density exhibited by TiO2 nanotubes under similar conditions. The optimal photocatalytic rate was achieved with BiOI/TiO2 NCs processed after five SILAR cycles.

Solution-processed Sb2O3: A promising electrode material for high-performance supercapacitors and electrocatalysts

Easy accessibility, wide range of redox states, affordable cost, and simple synthesis methods of metal oxides have gained a significant interest in the domains of electrochemical supercapacitors and electrocatalysts. The successive ionic layer adsorption and reaction (SILAR) chemical synthesis approach has been introduced to preparing nanocrystalline antimony oxide (Sb2O3) for both energy storage and water splitting applications. The Sb2O3 electrode demonstrates a remarkable specific capacitance of 3011 F/g at a current density of 2 A/g in a 1 M solution of potassium hydroxide (KOH). The current design of the Sb2O3//Bi2O3 (bismuth oxide) asymmetric electrochemical supercapacitor device has endowed a specific capacitance of 391 F/g, a maximum energy density of 78.2 Wh/Kg at a power density of 1000 W/Kg, and an outstanding capacitance retention of 77 % even after 5000 redox cycles. The Sb2O3 electrode demonstrates outstanding performance in the oxygen evolution process at a current density of 10 mA cm2, with an overpotential of 206 mV. The Sb2O3 as an electrocatalyst also exhibits exceptional results in the hydrogen evolution reaction with an overpotential of 124 mV/dec. Both of these electrochemical processes are distinguished by the evolution of oxygen which is capable of facilitating the process of water splitting to obtain clean energy for day by day growing population.

A comparative analysis of solid-state quantum dot-sensitized solar cells employing various hole transport layers, metal contacts, and a sensitizer comprising PbS/CdS/ZnS quantum dots

Quantum dots, as a sensitizer in quantum dot-sensitized solar cells (QDSSCs), hold the promise of revolutionizing solar energy conversion. This research mainly focuses on employing PbS/CdS/ZnS quantum dots (QDs) as both light harvesters and passivation layers in QDSSCs, which are directly synthesized onto the pre-deposited TiO2 substrate through the Successive Ionic Layer Adsorption and Reaction (SILAR) technique. Particularly, the sample with a composition of 2 cycles of PbS, 6 cycles of CdS, and 2 cycles of ZnS (2/6/2) exhibited a wide-ranging and intense absorption spectrum, attributed to the reduction in band gap with escalation in number of SILAR cycles. The prepared samples underwent analysis through characterization methods, including SEM and XRD, and the elemental composition was examined using EDX spectroscopy. Subsequently, the 2/6/2 sample was employed as a sensitizer, with P3HT and PEDOT:PSS serving as the hole transport layers (HTL). For the metal contacts, thermally evaporated gold (Au), silver (Ag), and Ag paste were used in the fabrication of six distinct devices. FTO/TiO2/PbS/CdS/ZnS/P3HT/Au shows the best performance demonstrating PCE of 2.17 %, Jsc of 7.9 mA/cm2 Voc of 0.54 V and FF of 0.51. However, overall efficiency dropped significantly for other configurations. Additionally, impedance spectroscopic analysis revealed a notably low series resistance for the P3HT/Au configuration.

Miniaturized inkjet-printed flexible ion-selective sensing electrodes with the addition of graphene in PVC layer for fast response real-time monitoring applications

In this letter, we propose a miniaturization scheme of inkjet printed ionic sensing electrodes by adding graphene into the ion-selective PVC film not only to reduce the impedance of the ionic liquid layer of the electrode but also to increase the electrode capacitance for the reduction of the response time. Based on the scheme, we present a fully inkjet-printed electrochemical ion-selective sensor comprising a working electrode and reference electrode, which are inkjet-printed Ag NPs/PEDOT:PSS-graphene/PVC-graphene and Ag/AgCl(s)/ionic liquid PVC-graphene layer structures, respectively. The printed ion-selective working electrode has been miniaturized to a size of 22,400 μm2 equivalent to a square shape of ∼150 × 150 μm2 comparable to the size of a human cell. By adding graphene to the ion selective PVC film, more than 90 % charge transfer resistance reduction can be achieved and the shunt capacitance is increased by 3.4-fold in shunt capacitance compared to the film without graphene, thereby more than 33 % reduction of the response time required to reach equilibrium. Meanwhile, these miniaturized potassium sensors using the working electrodes with/without adding graphene have been integrated with in-lab signal-processing and wireless-transmission module to yield similar results to the one measured by commercial electrochemical workstation showing a great potential for real-time monitoring in portable clinical trials. Specifically, the proposed sensor utilizing graphene-enhanced electrodes demonstrates a linearity uncertainty of 2.9 mV, which is approximately half of the uncertainty observed in the sensors lacking graphene integration.

Surface Chemistry of a [C2C1Im][OTf] (Sub)Wetting Layer on Pt(111): A Combined XPS, IRAS, and STM Study.

The concept of a solid catalyst with an ionic liquid layer (SCILL) is a promising approach to improve the selectivity of noble metal catalysts in heterogeneous reactions. In order to understand the origins of this selectivity control, we investigated the growth and thermal stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethanesulfonate [C2C1Im][OTf] films on Pt(111) by infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) in time-resolved and temperature-programmed experiments. We combined these spectroscopy experiments with scanning tunneling microscopy (STM) to obtain detailed insights into the orientation and adsorption geometry of the ions in the first IL layer. Furthermore, we propose a mechanism for the thermal evolution of [C2C1Im][OTf] on Pt(111). We observe an intact IL layer on the surface at temperatures below 200 K. Adsorbed [C2C1Im][OTf] forms islands, which are evenly distributed over the surface. The [OTf]- anion adsorbs via the SO3 group, with the molecular axis perpendicular to the surface. Anions and cations are arranged next to each other, alternating on the Pt(111) surface. Upon heating to 250 K, we observe changes in geometry and structural distribution. Whereas at low temperature, the ions are arranged alternately for electrostatic reasons, this driving force is no longer decisive at 250 K. Here, a phase separation of two different species is discernible in STM. We propose that this effect is due to a surface reaction, which changes the charge of the adsorbates. We assume that the IL starts to decompose at around 250 K, and thus, pristine IL and decomposition products coexist on the surface. Also, IRAS and XPS show indication of IL decomposition. Further heating leads to increased IL decomposition. The reaction products associated with the anions are volatile and leave the surface. In contrast, the cation fragments remain on the surface up to temperatures above 420 K.

Generalized Helmholtz model describes capacitance profiles of ionic liquids and concentrated aqueous electrolytes.

In this work, we propose and validate a generalization of the Helmholtz model that can account for both "bell-shaped" and "camel-shaped" differential capacitance profiles of concentrated electrolytes, the latter being characteristic of ionic liquids. The generalization is based on introducing voltage dependence of both the dielectric constant "ϵr(V)" and thickness "L(V)" of the inner Helmholtz layer, as validated by molecular dynamics (MD) simulations. We utilize MD simulations to study the capacitance profiles of three different electrochemical interfaces: (1) graphite/[BMIm+][BF4-] ionic liquid interface; (2) Au(100)/[BMIm+][BF4-] ionic liquid interface; (3) Au(100)/1M [Na+][Cl-] aqueous interface. We compute the voltage dependence of ϵr(V) and L(V) and demonstrate that the generalized Helmholtz model qualitatively describes both camel-shaped and bell-shaped differential capacitance profiles of ionic liquids and concentrated aqueous electrolytes (in lieu of specific ion adsorption). In particular, the camel-shaped capacitance profile that is characteristic of ionic liquid electrolytes arises simply from combination of the voltage-dependent trends of ϵr(V) and L(V). Furthermore, explicit analysis of the inner layer charge density for both concentrated aqueous and ionic liquid double layers reveal similarities, with these charge distributions typically exhibiting a dipolar region closest to the electrode followed by a monopolar peak at larger distances. It is appealing that a generalized Helmholtz model can provide a unified description of the inner layer structure and capacitance profile for seemingly disparate aqueous and ionic liquid electrolytes.