Low Potential Range Research Articles

Analyzing the Temperature Dependence of Titania Photocatalysis: Kinetic Competition between Water Oxidation Catalysis and Back Electron-Hole Recombination.

This study examines the kinetic origins of the temperature dependence of photoelectrochemical water oxidation on nanostructured titania photoanodes. We observe that the photocurrent is enhanced at 50 °C relative to 20 °C, with this enhancement being most pronounced (by up to 70%) at low anodic potentials (<+0.6 V vs RHE). Over this low potential range, the photocurrent magnitude is largely determined by kinetic competition between water oxidation catalysis (WOC) and recombination between surface holes and bulk electrons (back electron-hole recombination, BER). We quantify the BER process by transient photocurrent analyses under pulsed irradiation. Remarkably, we find that the kinetics of BER (∼90 ms half-time) are independent of temperature. In contrast, the kinetics of WOC, determined from the analysis of the photoinduced absorption of accumulated surface holes, are found to accelerate up to 2-fold at 50 °C relative to 20 °C. We conclude that the enhanced photocurrent densities observed in the low-applied potential region result primarily from the accelerated WOC, reducing losses due to the competing BER pathway. At higher applied potentials (>+0.6 V vs RHE), a smaller (∼10%) enhancement in photocurrent density is observed at 50 °C relative to 20 °C. Photoinduced absorption studies, correlated with studies using triethanolamine as a hole scavenger, indicate that this more modest enhancement at anodic potentials primarily results from an enhanced charge separation efficiency. We conclude by discussing the implications of these results for the practical application of photoanodic WOC under solar irradiation, influenced by these temperature-independent and -dependent underlying kinetic processes.

Multiplexed Fluoro-electrochemical Single-Molecule Counting Enabled by SiC Semiconducting Nanofilm.

A major challenge for ultrasensitive analysis is the high-efficiency determination of different target single molecules in parallel with high accuracy. Herein, we developed a quantitative fluoro-electrochemical imaging approach for direct multiplexed single-molecule counting with a SiC-nanofilm-modified indium tin oxide transparent electrode. The nanofilm could control local pH through proton-coupled electron transfer in a lower potential range and further induce direct electrochemical oxidation of the dye molecules with a higher applied potential. The fluoro-electrochemical responses of immobilized single molecules with different pH values and redox behaviors could thus be distinguished within the same fluorescence channels. This method yields nonamplified direct counting of single molecules, as indicated by excellent linear responses in the picomolar range. The successful distinction of seven different randomly mixed dyes underscores the versatility and efficacy of the proposed method in the highly accurate determination of single dye molecules, paving the way for highly parallel single-molecule detection for diverse applications.

Influence of Simple Salts on Solvent Reduction Stability at Mg‐Alloy Anodes Interface: A Potential‐Dependent DFT Study

AbstractThe significance of incorporating anion species into electrolyte solvation structures, particularly with doubly charged Mg2 + ions, is investigated using the grand canonical density functional theory (GC‐DFT) approach. In an extension of previously established methodology, the work explores the thermodynamic stability in acetonitrile (AN) at the interface with Mg3Bi2 and Mg2Sn. Two different anions, TFSI− and , are strategically incorporated based on energy comparisons. Despite the known chemical compatibility of alloy anodes with the electrolyte solution, the research reveals a novel form of solvent degradation, which is also reported in the case of pure Mg anode with conventional electrolytes. Notably, the AN molecule adjacent to anion species exhibits reduced susceptibility to reduction (−0.8 – −0.4 V vs Mg2 +/Mg) in the lower potential range in comparison with the solvation structure of full dissociation. Charge density difference and density of states analyses detail solvent molecules becoming electrophilic, with the LUMO overlapping with the Fermi level at lower potentials when the electrostatic interaction with anion species are considered. Experimental studies using nuclear magnetic resonance (NMR) spectroscopy and linear sweep voltammetry (LSV) validate the theoretical results, providing a comprehensive understanding. This methodology, augmenting prior approaches, provides valuable guidance for electrolyte composition based on predominant solvation structures in multivalent solutions.

Determining kinetics of electrochemical carbon dioxide reduction to carbon monoxide with scanning electrochemical microscopy

This study reports on determining kinetics of electrochemical reduction CO2 to CO on Au catalysts using the substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM). We introduced a simple but effective method based on transient technique to obtain a series of apparent heterogeneous rate constants k based on Fick’s second law by controlling the tip-substrate distance and the voltage of the substrate electrode within the SECM framework. By analysis the transient current recorded during the chronoamperometric characterization, we can successfully determine the apparent rate constant k for the simplified total conversion process of CO2 + 2H+ + 2e- → CO + H2O onto Au catalyst electrode serving as an example, which increases from 5.02 × 10–2 cm⋅s−1 to 7.16 × 10–2 cm⋅s−1 in the low potential range of −2.2 to −2.6 V (vs. Pt/PPy) and decreases to 6.54 × 10-2 cm⋅s−1 at –2.8 V (vs. Pt/PPy). The method proposed here can be applied to quantitatively analyze the kinetic of CO2 electrochemical reduction reaction, and thus provide a useful tool to guide the synthesis of catalyst as well as in-situ performance evaluation.

A Soil Hydraulic Conductivity Equation Incorporating Adsorption and Capillarity

A soil’s hydraulic conductivity is a highly nonlinear function of water content, decreasing many orders of magnitude from its saturated state to dry state. This nonlinearity is a macroscopic manifestation of microscopic soil properties of pore structure, pore connectivity, and mineral–water interaction. These microscopic soil properties are underpinned by two distinct soil–water interaction mechanisms: adsorption and capillarity. Herein, a soil hydraulic conductivity equation was developed by incorporating capillary pore flow and adsorptive film flow. The capillary pore flow is captured via a model of bundle of cylindrical capillaries, whereas the adsorptive film flow is established using a film thickness function incorporating adsorption mechanisms of the electric double layer, van der Waals, surface hydration, and cation hydration potentials. The transition between adsorptive film flow and capillary flow is delineated by a water cavitation probability function. The proposed soil hydraulic conductivity equation automatically can fulfill the five necessary physical constraints imposed by underlying soil–water interaction characteristics. The proposed hydraulic conductivity equation can capture the hydraulic conductivity data very well for a wide array of soils, and outperforms several established soil hydraulic models in full matric potential ranges, especially in the low matric potential range in which adsorptive film flow is dominant.

Enhanced Energy Storage in Lithium-Metal Batteries via Polymer Electrolyte Polysulfide-Polyoxide Conetworks.

The present article entails a novel concept of storing extra energy in a multifunctional polymer electrolyte membrane (PEM) beyond the storage capacity of a cathode, which is achieved by so-called "prelithiation" upon simply deep discharging to a low potential range of a lithium-metal electrode (i.e., -0.5 to 0.5 V). This unique extra energy-storage capacity has been realized recently in the PEM consisting of polysulfide-co-polyoxide conetworks in conjunction with succinonitrile and LiTFSI salt that facilitate complexation via ion-dipole interaction of dissociated lithium ions with thiols, disulfide, or ether oxygen of the conetwork. Although ion-dipole complexation may increase the cell resistance, the prelithiated PEM provides excess lithium ions during oxidation (or Li+ stripping) at the Li-metal electrode. Once the PEM network is fully saturated with Li ions, the remaining excess ions can move through the complexation sites at ease, thereby affording not only facile ion transport but also extra ion-storage capacity within the PEM conetwork. Of particular interest is that the lithiated polysulfide-co-polyoxide polymer network-based PEM exhibits a high conductivity of 1.18 × 10-3 S/cm at ambient, which can also store extra energy with a specific capacity of about 150 mAh/g at a 0.1C rate in the PEM voltage range of 0.01-3.5 V in addition to 165 mAh/g at 0.2C of an NMC622 (nickel manganese cobalt oxide) cathode (i.e., 2.5-4.6 V) with a Coulombic efficiency of approximate unity. Moreover, its Li-metal battery assembly with an NMC622 cathode exhibits a very high specific capacity of ∼260 mAh/g at 0.2C in the full battery range of 0.01-5 V, having a higher Li+ transference number of 0.74, suggestive of domination by the lithium cation transport relative to those (0.22-0.35) of organic liquid electrolyte lithium-ion batteries.

Phosphorus and nitrogen doped CoNi nanocrystals supported on carbon based materials for electro- reduction of CO2 to syngas with controllable CO/H2

The products of electrocatalytic CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER) are the raw materials CO and H2 of synthesis gas respectively. The synthesis gas can generate usable fuel by Fischer Tropsch method to realize the carbon cycle. At present, it is still challenging to control the synthesis gas generation in the low potential and wide potential range. In order to solve this problem, we used a simple template method to embed different proportions of Ni and Co elements in the three-dimensional network structure of carbon carrier, between − 0.55 to − 1.15 V vs RHE, to generate synthetic gas with an adjustable CO/H2 ratio of 0.3–3. When Ni/Co ratio is 2:1(CoNi2 @NCP), the ratio of CO/H2 is kept at 1–3. At the potential of − 1.05 V vs RHE, the Faraday efficiency of CoNi2 @NCP catalyst to produce CO reaches 57 %, and that of H2 reaches 25 %. When the ratio of Ni-Co is 1:1 and 2:1, it can be used to produce methanol, ethanol and other alcohol products. Catalysts with different proportions can generate different synthesis gases at different potentials, which can be better used to generate downstream thermochemical synthesis of methane, ethylene, and alcohols. The sources of CO2RR and HER can be determined as Ni−Nx and Co−Nx sites by electrochemical analysis.

Covalent organic framework@graphene composite as a high-performance electrode for Li-ion batteries

ABSTRACT As emerging candidates for the electrode materials of next-generation rechargeable batteries, covalent organic frameworks (COFs) have large charge capacity, wide ion diffusion paths and low potential range. However, organic electrodes generally suffer from low conductivity. Graphene (G) possesses great strength, flexibility and has been widely used as a type of conductive additive due to its remarkable electrical conductivity. Here we propose a composite constructed by a certain kind of COF and a pristine G sheet (COF@G), the characteristics of which have been systematically investigated based on density functional theory calculations and molecular dynamics simulations. Results indicate that the COF@G (COF/G, COF/COF/G, COF/G/G) can exhibit good electronic conductivity and ultrahigh capability, which can be used as high-performance electrodes of Li-ion batteries. For Li-ions (Li+), they can provide strong adsorption sites and smooth diffusion channels leading to high specific capacity and good rate capability. More importantly, the coupling interaction of the COF and the G can greatly inhibit the structure changes of the COF during the lithiation process, and the volumetric change rate is less than 23%. Among them, the COF/G is the most suitable for Li+ adsorption and corresponding theoretical capacity can reach 353 mAh/g.

Multifunctional polymer electrolyte membrane networks for energy storage via ion-dipole complexation in lithium metal battery

A novel concept of energy storage is presented involving ion-dipole complexation within multifunctional polymer electrolyte membrane (PEM), consisting of polyethylene glycol diacrylate (PEGDA) and succinonitrile (SCN) plasticizer and lithium bis-trifluoromethane sulfonyl imide (LiTFSI) salt. A similar complexation of lithium ions with ether oxygen and amine moieties occurs in the thermally cured poly(ethylene glycol) diglycidyl ether (PEGDGE) - polyether amine (Jeffamine D400, 2-arm) co-network. By virtue of the network functional groups, the ion transport is hindered which may be viewed as temporally holding of the Li ions, reminiscent of ion storage. Although some Li ions may be partially immobilized due to ion-dipole complexation, upon prelithiation via deep discharging the lithium metal/PEM/lithium iron phosphate (LFP) battery assembly to the low potential range of 0.01–0.5 V (i.e., oxidation at the Li metal anode), excess mobile Li ions become available that can travel to the cathode through the Li+ saturated complexation sites at ease, exhibiting high ionic conductivity with energy storage capability within the PEM matrix. Another way of supplying Li ions to PEM is through diffusion driven by ion concentration gradient between the two-layer PEM composite composed of a high salt concentration layer and a no-salt layer. The CV measurement was carried out as a function of aging time on the bilayer composite in the PEM potential range of 0.01 to 2.5 V, which indeed revealed a systematic emergence of redox reaction peaks, thereby validating the energy storing concept of the multifunctional PEM network.

Simultaneous Determination of Ranitidine and Metronidazole at Low Potential Using an Acid‐Activated Glassy Carbon Electrode

AbstractA simple, highly sensitive and inexpensive electrochemical method was established using an activated glassy carbon electrode (AGCE) in an acidic condition for the determination of ranitidine (RT) and metronidazole (MT) simultaneously at a low potential range. The AGCE was characterized using various techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and morphology was studied through field‐emission scanning electron microscope (FE‐SEM). The AGCE exhibited an electrocatalytic behavior towards the reduction of RT and MT in 0.5 M acidic solution. Both CV and DPV responses for the mixture of RT and MT gave well‐resolved peaks at low potential. Analysis of these experiments helps us to predict interactions that took place on the surface of AGCE and RT and MT with each other for having different types of functional groups. Furthermore, AGCE also promoted the electron transfer process. The linear dynamic range of MT and RT was 0.5–580 μM and 0.5–500 μM, respectively with the regression coefficient 0.99. The detection limit (S/N=3) calculated for MT and RT was 0.062 μM and 0.13 μM, respectively. Decent results were obtained from the reproducibility and stability test. The performance of the sensor was evaluated for the possible interferences which show high selectivity. Additionally, the real sample analysis was carried out to understand our sensor‘s applicability in real life.

Electrochemical formic acid oxidation catalyzed by graphene supported bimetallic Pd-Ni clusters: The role of Ni content and the hydrogen coverage effect

By means of periodic density functional theory calculations, we have investigated the electrocatalytic formic acid oxidation (FAO) on graphene supported Pd-Ni catalysts and elucidate the detail about the role of Ni content in different Pd-Ni atomic ratio and the hydrogen coverage effect. The FAO reaction often onsets at low oxidation potential range, where deposition of hydrogen is alive and affect the catalytic performance of Pd-Ni clusters, accordingly, the FAO reaction on varied H* ratio Pd-Ni clusters accompanying with enhanced external potential is also considered. In our calculation, the H* saturated situation would suppress the formation of COOH* much more than that of HCOO*, even controlling the reaction energy of HCOO* from HCOOH become moderate in FAO reaction. In addition, the potential requirements to proceed the FAO reaction on Pd10-gra and Pd8Ni2-graphene are similar but Ni content could also suppress formation of COOH* and enhance the interaction between Pd8Ni2-graphene and HCOO* species. Pd6Ni4-grahene model is another choice for FAO reaction, in which the HCOO* species on clean Pd6Ni4-graphene model has lowest onset potential of 0.18 V for HCOO* deprotonation to CO2 in all of our models. However, excess Ni content would cause Ni exposed on Pd2Ni8-grahene, where the HCOO* is downhill in energy with a larger onset potential of 0.59 V for the deprotonation of HCOO*, but the hydride formation of 8H* and 9H* Pd2Ni8-graphene could overcome the question.

Na3MnTi(PO4)3/C composite as an anode for Na-ion batteries with superior rate performance and long-term span

Polyanionic phosphates, one of the Na superionic conductors (NASICON) structured materials, have become the research focus due to their good structural stability, thermal stability, excellent electrochemical performance and long cycle span. Na3MnTi(PO4)3 (NMTP) has been reported as a promising cathode, showing three-electron reaction during cycling with three redox couples of Mn3+/4+ (4.0 V vs. Na+/Na) and Mn2+/3+ (3.5 V) and Ti3+/4+ (2.1 V). Note that the lower redox couple of Ti2+/3+ (0.4 V), due to the further reduction of titanium, endows NMTP the characteristic as an anode for Na-ion batteries. In this work, the Na storage performance and reaction mechanism of NMTP/C in the low potential range of 0.01 – 3.0 V are explored. The NMTP/C composite exhibits a reversible specific capacity of 200 mAh g−1 at 0.1 C, which is superior to the Na3V2(PO4)3/C anode (170 mAh g−1) in the same voltage range. Attractively, NMTP/C composite provides a specific discharge capacity of 71 mAh g−1 at 10.0 C and remains a capacity retention rate of 93.4% after 3000 cycles, showing the superior rate performance and long-term stability. In addition, ex situ XRD and HRTEM are used to reveal the structural evolution of two-phase and single-phase solid solutions during cycling. Our findings confirm that the lower voltage plateau of Ti2+/3+ doubles the sodiation capacity of NMTP and verifies its feasibility as a promising anode for Na-ion batteries.

(Digital Presentation) Accelerated Degradation Mechanism of Ni-Rich Ncm Cathode Materials at High and Low Voltage Range Combined Cycling for Li-Ion Batteries

Lithium-ion batteries are widely used as power sources in electric buses, railways, ferries, and other mass transportation systems. To meet the energy needs of these infrastructure systems, it is important to realize battery control that enables high-energy operation for long periods of time. The high-capacity Ni-rich cathode material NCM811 (LiNi0.8Co0.1Mn0.1O2) has attracted research interest as a candidate high-energy-density cathode material. However, NCM811 has been reported to have some degradation problems, especially when operating at potential above 4.2 V versus Li/Li+1).Furthermore, the safety of NCM811 becomes compromised with time. Therefore, understanding the aging mechanism and predicting battery aging behavior are required for effective battery control. We have found that operating NCM811 cathodes at the combination of the potential higher than 4.2 V and lower potential less than 3.6 V that accelerates aging, leading to substantial capacity loss and increased resistance. However, aging was mitigated when NCM811 batteries were operated at a higher or lower potential range. Electrochemical and chemical analyses were performed to clarify the aging mechanism. We prepared 1-Ah LTO/NCM811 pouch cells. Charge/discharge cycling tests were carried out using various state-of-charge (SOC) ranges (SOC0-100%, SOC20-100%, and SOC0-70%) at a 3C rate at 65°C. When the cell was charged at SOC100% and SOC0%, the cathode potential was set to above 4.2 V and to below 3.6 V. The capacity retention and DC resistance (DCR: SOC50%, 0.2 sec) for these cells are shown in Figure1a. The capacity retention of the cell after 1000 cycles at SOC0-100% cycling test was about 75% for the initial capacity. However, a high capacity retention of 93% was obtained at SOC20-100% cycling, despite the cell was charged at SOC100% of 1000 times. The capacity retention of SOC0-70% cycling was nearly 100%. DCR increased 2.5-times after 1000 cycles at SOC0-100% cycling, which was higher increase than that of SOC20-100% cycling and SOC0-70% cycling. To clarify the mechanism, the cathode was removed from the deteriorated pouch cells and its electrochemical properties were investigated using a three-electrode glass beaker cell. The cell was assembled using the cathode and lithium metal as a counter electrode, and a reference electrode was also prepared. The lithium-diffusion coefficient of NCM811 at the time of preparation and after 1000 cycles was measured using the galvanostatic intermittent titration technique method. In the case of a NCM811 cathode operated at SOC0-100% for 1000 cycles, there was little change for the lithium-diffusion coefficient of x < 0.8 in LixNi0.8Co0.1Mn0.1O2, but that of x > 0.8 decreased to less than 1/10. Changes in the crystal structure of the NCM811 particle surface were analyzed by scanning transmission electron microscopy–electron energy loss spectroscopy (STEM-EELS). The thickness of the surface structural change layer was calculated from the EELS spectrum. Also, the thickness and composition of surface film was analyzed by hard X-ray photoelectron spectroscopy (HAX-PES). This measurement was performed at the SPring-8 synchrotron radiation facility. From the STEM-EELS analyses, in the case of SOC0-100% cycling, the surface crystal structure of NCM811 changed from the layered type to the rock-salt or spinel-layer type. The thickness of this transition layer increased by 7 nm compared from beginning. In the case of SOC0-70% cycling, the thickness increased by only 2 nm. It is expected that the cathode operated above 4.2 V at SOC0-100% cycling. From the HAX-PES analysis, the film thickness increased by 20 nm from the initial condition after SOC0-100% cycling. But, after SOC20-100% cycling and SOC0-70% cycling, the film thickness increased was suppressed than that. Based on the results of these analyses, we proposed the following model. In the first step, the structure change of NCM811 was accelerated at high potential. As the rock-salt layer disturbed lithium diffusion, the diffusional resistance increased and the capacity during discharge decreased. In the second step, when NCM811 subjected to a higher potential was discharged to a lower potential, the lithium can’t be intercalated smoothly at the surface x > 0.8 in LixNi0.8Co0.1Mn0.1O2. As a result, the lithium near the surface reacts with electrolyte, forming a film on the NCM811 surface. As the lithium was consumed by the film-growth reaction, the cathode operating potential increased, which accelerated the first step mechanism. The combination of the first and second steps accelerated aging. But this aging can be minimized by controlling the operating voltage. Understanding of the aging mechanism will enable accurate prediction of deterioration.[1]F. Friedrich, B. Strehle, etc, Journal of The Electrochemical Society, 166, A3760-A3774 (2019) Figure 1

Carbon Nanosheets Derived from Reconstructed Lignin for Potassium and Sodium Storage with Low Voltage Hysteresis

Lignin is the second most abundant and the only nature polymer rich in aromatic units. Although aromatic unit-rich precursors often yield soft carbon after carbonization, the side chains in lignin crosslink with the aromatic units and form a rigid 3D structure which eventually leads to hard carbons. Through a graphene oxide-catalyzed decomposition and repolymerization process, we successfully reconstructed lignin by partially tailoring the side chains. Compared to directly carbonized lignin, the carbonized reconstructed lignin possesses significantly fewer defects, 86% fewer oxygen-functionalities, 82% fewer micropores, and narrower interlayer space. These parameters can be tuned by the amount of catalysts (graphene oxide). When tested as anode for K-ion and Na-ion batteries, the carbonized reconstructed lignin deliveries notably more capacity at low-potential range (especially for Na-storage), shows much-improved performance at high current density, and most importantly, reduces voltage hysteresis between discharge and charge process by more than 50%, which is critical to the energy efficiency of the energy storage system. Our study reveals that the voltage hysteresis in K-storage is much severer than that in Na-storage for all samples. For practical K-ion battery applications, the voltage hysteresis deserves more attention in future electrode materials design and the reconstruct ion strategy introduced in this work provide potential low-cost solution. Figure 1

A New TiO with in-Situ Transformed Rutile TiO2 Nanothorns As a Superb Anode Material for Lithium-Ion Battery

Developing high-performance anodes is highly desired to meet the recent ever-increasing demands for lithium-ion battery (LIB). Herein we report a uniquely integrated hybrid structure of rutile TiO2 (r-TiO2) nanothorns in situ grown over a new porous and conductive TiO core, which is generated from pyrolysis of anatase TiO2 with Mg metal at 650℃. The new hybrid exhibits superb LIB performance as an anode with high reversible capacity and almost no capacity decay during 1000 cycles at a high current density of 20 C (4000 mA g-1). Two independent reactions of intercalation and pseudocapacitive interaction are confirmed to occur in the composite of the r-TiO2 and TiO, respectively. In particular, the excellent rate capability along with long cycle life enables the new hybrid to have ultrafast charging of the system. Furthermore, the hybrid with the job-sharing property exhibits stable charge-discharge performance over a wider potential window range of 0.01 to 3.0 V, particularly even in the low potential range of 0.01~1.0 V, which usually causes irreversible Li-intercalation and rapid capacity decay for pristine TiO2. All the properties including the wider potential window allows the hybrid to realize the highest electrochemical performance that titanium oxides have ever achieved so far.

Novel Ni foam catalysts for sustainable nitrate to ammonia electroreduction

Electrochemical nitrate reduction (NO3−RR) is considered a promising approach to remove environmentally harmful nitrate from wastewater while simultaneously producing ammonia, a product with high value. An important consideration is the choice of catalyst, which is required not only to accelerate NO3−RR but also to direct the product selectivity of the electrolysis toward ammonia production. To this end, we demonstrate the fabrication of novel Ni foam catalysts produced through a dynamic hydrogen bubble template assisted electrodeposition process. The resulting foam morphology of the catalyst is demonstrated to crucially govern its overall electrocatalytic performance. More than 95% Faradaic efficiency of ammonia production was achieved in the low potential range from –0.1 to −0.3 V vs. RHE. Hydrogen was found to be the only by-product of the nitrate reduction. Intriguingly, no other nitrogen containing products (e.g., NO,N2O, or N2) formed during electrolysis, thus indicating a 100% selective (nitrate→ammonia) conversion. Therefore, this novel Ni foam catalyst is a highly promising candidate for truly selective (nitrate→ammonia) electroreduction and a promising alternative to mature copper-based NO3−RR benchmark catalysts. Excellent catalytic performance of the novel Ni foam catalyst was also observed in screening experiments under conditions mimicking those in wastewater treatment.

Multicolored and durable electrochromism in water soluble naphthalene and perylene based diimides

Organic small molecules are advantageous in electrochromism as they exhibit high coloration efficiency, fast switching with vivid colors range at low potential range. However, the main problems in this type of electrochromes are film processing and dissolution of the compound during operation to restrict the durability. Herein, we have successfully synthesized two water soluble sulfonate group containing arylene diimides; NDI-cored NTSA and PDI-cored PRSA and comprehensively characterized by different spectroscopic techniques, morphological investigation and electrochemical characterizations, etc. Two diffusion controlled quasi-reversible redox waves are envisaged in both the compounds for stepwise reduction of neutral species to mono-anion radical and mono-anion radical to di-anion radical formation. Both NTSA and PRSA films show multichromic EC behavior in low potential range of +0.5 to −1.5 V with high optical contrast and high coloration efficiencies when measured in solution electrolytes. The durability test unveils the 80% retention of the optical contrast for NTSA, while 82% retention of the same for PRSA even after 800 cycles. The solid state ECD made of PRSA film also divulges the similar multi-chromic EC behavior. The results can provide a viable approach to design the high performance cathodically colored PDI and NDI ECMs as the potential candidate for energy-saving multi-colored smart window. • Synthesis of water soluble redox-active naphthalene and perylene diimides. • Both the compounds (NTSA and PRSA) display multicolored electrochromism. • Durable electrochromism with high optical contrast and coloration efficiency. • Solid state devices also show multicolored electrochromism at low working voltage.

An alternative electron-donor and highly thermo-assisted strategy for solar-driven water splitting redox chemistry towards efficient hydrogen production plus effective wastewater treatment

An alternative technology has been sought for highly efficient and sustainable hydrogen production and wastewater treatment worldwide. This paper is focused on the intersection of solar energy, wastewater treatment and hydrogen production. The solar thermo-assisted and electron-donor alternative strategy was conducted for water-splitting redox chemistry to target highly efficient hydrogen production and effective wastewater treatment. The thermodynamic calculation displays that the solar thermal application and shuttle sulfide electron donor alternative are favorable for the hydrogen production and sulfide-to-sulfate oxidation by the falling trend in the potential (from 1.5V to 0.6V). The curves revealed that high current peaks in the low potential range were dominated by the thermal-assisted process and the alternative of the oxidation half-reaction. The experiments illustrated that solar thermal utilization and sulfide donors were dominant factors for the high efficiencies. Under the outdoor sunlight, the high hydrogen production rate and sulfide conversion efficiency were experimentally achieved at rates of 0.25 mL/h H2 and 93% sulfide-to-sulfate oxidation, reasonably more than that of the direct electrochemical water splitting to hydrogen (nearly no evolution) under the same applied bias (＜1.2V). The system realized that one sustainable technology conducts simultaneously both highly efficient hydrogen production and highly effective water treatment.

Towards moss biocrust effects on surface soil water holding capacity: Soil water retention curve analysis and modeling

As ecosystem engineers in drylands, biocrusts possibly generate great influences on surface soil water holding capacity and availability, but these effects have not yet been sufficiently investigated, especially through analyzing and modeling their soil water retention curve (SWRC). On the Loess Plateau of China, the naturally developed moss biocrusts and surface bare soil were sampled in five replicates on loess soil and aeolian sand respectively, and their SWRCs from saturation (soil water potential = 0 hPa) to dry (soil water potential = −15,000 hPa) were measured with a sandbox (low water potential range) in combination with a pressure plate (high water potential range). The measured SWRCs were compared to the van Genuchten (VG), Brooks and Corey (BC), and Log-Normal Distribution (LND) models, and the model with best performance was adopted to further determine the effects of biocrusts on surface soil water holding capacity and water availability through comparing the differences in soil water content (θ) at specific water potentials between the biocrusts and uncrusted soil. Our results showed that (i) the biocrusts always had higher θ as compared with the bare soil across the whole water potential range, and the increasing effects of the biocrusts was much stronger on aeolian sand (165%) in comparison to that on loess soil (15%). (ii) As compared with the bare soil, the saturated water content, field capacity, wilting point, and available water content of the aeolian sand increased by 52%, 256% (0.192 vs. 0.054 cm3 cm−3), 65%, and 1000% by the biocrusts, respectively; while that of the loess soil increased by 28%, 9% (0.240 vs.0.220 cm3 cm−3), 27%, and 8% by the biocrusts, respectively. (iii) The increased water holding capacity of the biocrusts was possibly attributed to their higher percentage (18% vs. 16%) of microscopic pores (0.3–5 μm) on the loess soil and their increasing (16% vs. 1%) microscopic pores and decreasing (18% vs. 50%) medium pores (30–75 μm) on the aeolian sand. (iv) The VG and LND models performed better (R2 > 0.98, RMSE ≤ 0.019 cm3 cm−3, RE ≤ 7.4%) than the BC model in simulating the SWRCs of the biocrusts and bare soil, and their fitting errors were mostly distributed in the high (−500 to −1000 hPa) and low (<−5000 hPa) water potential ranges. As indicated by SWRCs, we conclude that biocrusts greatly increase surface soil water holding capacity and water availability, leading in turn to a positive feedback mechanism of the biocrusted layer, which may affect surface hydropedological process (e.g., infiltration and evaporation) in drylands.

Carbon nanosheets derived from reconstructed lignin for potassium and sodium storage with low voltage hysteresis

Lignin is the second most abundant and the only nature polymer rich in aromatic units. Although aromatic-unit-rich precursors often yield soft carbon after carbonization, the side chains in lignin crosslink with the aromatic units and form a rigid three-dimensional (3D) structure which eventually leads to hard carbons. Through a graphene oxide-catalyzed decomposition and repolymerization process, we successfully reconstructed lignin by partially tailoring the side chains. Compared to directly carbonized lignin, the carbonized reconstructed lignin possesses significantly fewer defects, 86% fewer oxygen-functionalities, 82% fewer micropores, and narrower interlayer space. These parameters can be tuned by the amount of catalysts (graphene oxide). When tested as anode for K-ion and Na-ion batteries, the carbonized reconstructed lignin delivers notably higher capacity at low-potential range (especially for Na-storage), shows much-improved performance at high current density, and most importantly, reduces voltage hysteresis between discharge and charge process by more than 50%, which is critical to the energy efficiency of the energy storage system. Our study reveals that the voltage hysteresis in K-storage is much severer than that in Na-storage for all samples. For practical K-ion battery applications, the voltage hysteresis deserves more attention in future electrode materials design and the reconstruct ion strategy introduced in this work provides potential low-cost solution.