High Scan Rates Research Articles

Treatment of carbon electrodes with Ti3C2Tx MXene coating and thermal method for vanadium redox flow batteries: a comparative study.

One of the significant challenges of vanadium redox flow batteries is connected to the negative electrode where the main reaction of V(ii)/V(iii) and the side reaction of hydrogen evolution compete. To address this issue, we used titanium carbide (Ti3C2Tx) MXene coating via drop-casting to introduce oxygen functional groups and metals on the carbon electrode surface. Characterization through scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the even distribution of Ti3C2Tx MXene on the electrodes and the presence of titanium and termination groups (-O, -Cl, and -F). The cyclic voltammetry analysis of MXene-coated electrodes showed more sharp electrochemical peaks for the V(ii)/V(iii) reaction than thermal-treated electrodes, even at relatively high scan rates. Notably, a relatively high reaction rate of 5.61 × 10-4 cm s-1 was achieved for the V(ii)/V(iii) reaction on MXene-coated electrodes, which shows the competitiveness of the method compared to thermal treatment (4.17 × 10-4 cm s-1). The flow battery tests, at a current density of 130 mA cm-2, using MXene-coated electrodes showed pretty stable discharge capacity for over 100 cycles. In addition, the voltage and energy efficiency were significantly higher than those of the system using untreated electrodes. Overall, this work highlights the potential application of MXene coating in carbon electrode treatment for vanadium redox flow batteries due to remarkable electrocatalytic activity and battery performance, providing a competitive method for thermal treatment.

Preparation of Spherical δ-MnO2 Nanoflowers by One-Step Coprecipitation Method as Electrode Material for Supercapacitor.

Spherical δ-MnO2 nanoflower materials were synthesized via a facile one-step coprecipitation method through adjusting the molar ratio of KMnO4 to MnSO4. The influence of the molar ratio of the reactants on the crystal structure, morphology, and electrochemical performances was investigated. At a molar ratio of 3.3 for KMnO4 to MnSO4, the spherical δ-MnO2 nanoflowers composed of nanosheets with the highest specific surface area (228.0 m2 g-1) were obtained as electrode materials. In the conventional three-electrode system using 1 M Na2SO4 as an electrolyte, the specific capacitance of the spherical δ-MnO2 nanoflowers reached 172.3 F g-1 at a current density of 1 A g-1. Moreover, even after 5000 cycles at a current density of 5 A g-1, the GCD curves remained essentially unchanged, and the specific capacitance still retained 86.50% of the maximum value. The kinetics of the electrode reaction were preliminarily studied through the linear potential sweep technique to observe diffusion-controlled contribution toward total capacitance. For the spherical δ-MnO2 nanoflower electrode material, diffusion-controlled contribution accounted for 65.1% at low scan rates and still remained significant at high scan rates (100 mV s-1), indicating excellent utilization efficiency of the bulk phase. The as-fabricated asymmetric supercapacitor HFC-7//MnO2-3.3-ASC presented a prominent specific energy of 16.5 Wh kg-1 at the specific power of 450 W kg-1. Even when the specific power reached 9.0 kW kg-1, the energy density still retained 9.5 Wh kg-1.

A fundamental study on cyclic voltammetry at porous carbon thin-film electrodes

Porous carbons represent an important group of electrode materials for electrochemical applications due to their high specific surface area, good conductivity, and intrinsic porosity. However, the often-neglected influence of the electrode porosity on the electrochemical results may lead to wrong interpretation of data. The aim of this work is therefore to provide comprehensive understanding of the effects of electrode porosity on cyclic voltammetry (CV) – a technique which is frequently used for initial characterization of novel electrode materials. Our approach consists of simulating experimental results, observed for the redox-reactions of [Fe(CN)6]3-/4− at porous CNT thin-film electrodes, with a mathematical model. The results demonstrate that the main difference between planar and porous electrode is the additional charge transferred in the porous electrode domain, which has the decisive contribution to the overall faradaic current at high scan rates. To further verify the applied model, the porosity of the porous CNT film is varied on purpose by changing the Nafion-Carbon-ratio (NCR). We are able to determine the electrochemically available pore volume (ECPV) of the electrode, which is strongly affected by the NCR, and correlate changes in the ECPV with changes in the scan-rate dependent CV. Moreover, we implement an approach for determination of reaction rate constants at porous electrodes, which was verified by simulated CV data. Evaluation of the experimental results shows that the reaction rate constant of the porous CNT material actually has the same order of magnitude as the planar glassy carbon substrate.

Superior compatibility of silicon nanowire anodes in ionic liquid electrolytes

Silicon nanowire anodes were investigated in lithium-metal cells using different electrolyte formulations based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and N -trimethyl-N -butyl-ammonium bis(fluoro sulfonyl)imide ionic liquids. The lithium insertion process in the silicon anode was analyzed by cyclic voltammetry measurements, performed at different scan rates and for prolonged cycles, combined with impedance spectroscopy analysis. A galvanostatic charge-discharge cycling test was performed to analyze the electrochemical performances using different types of ionic liquids. A study of the Solid Electrolyte Interphase layer on the silicon nanowire electrode surface was carried out through X-ray photoelectron spectroscopy. In general, the silicon anodes in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide-based electrolytes show very good reversibility, reproducibility, and efficiency in the lithiation process, even at high scan rates, and exhibit a reversible capacity exceeding 1,000 mA h g-1 after 2,000 charge-discharge cycles, corresponding to 46% of the initial value.

Electrochemical detection of phenacetin with graphite/boron-doped diamond electrode grown at high methane concentration

We have developed a composite electrode containing boron-doped diamond and high graphite content (HGBDD) by microwave plasma chemical vapor deposition system at high methane concentration. The electrode is applied to test the trace level of phenacetin. Scanning rate studies have exhibited that electrochemical oxidation is controlled by adsorption with scanning speed ranging from 20 to 100 mV s−1, while at a higher scanning rate, electrochemical oxidation is controlled by diffusion process. Voltammetry of phenacetin researched on the HGBDD electrode reveals the redox mechanism of phenacetin, the HGBDD has a high current response with a sensitive detection limit of 0.058 μM and a wide linear detection range of 0.5 μM - 400 μM. The high performance could be attributed to the presence of a higher carrier concentration for HGBDD electrode. Based on the density functional theory caculations, the graphite on the diamond surface could adsorb phenacetin strongly and provide more active sites for the redox reaction. Due to the unique properties of diamond, the electrode shows stability, repeatability, and accuracy for detecting phenacetin.

Unleashing asymmetric polyoxometalate redox activators on 2D interfaces for high-performance hybrid energy storage

Polyoxometalates (POMs) are an intriguing class of compounds with remarkable redox capabilities, making them prime candidates for energy storage applications. However, the challenge lies in their heightened solubility, which limits their direct use as electrode materials. The successful confinement of POMs into suitable templates becomes pivotal in creating supercapacitors with elevated energy and power densities. Our study showcases the successful integration of asymmetric POMs (Mo and W) onto two-dimensional (2D) templates, specifically graphene oxide and MXene. The synergy could benefit from the inherent charge storage capabilities of the high surface area 2D substrates that could provide a template for uniform dispersion of POMs enabling additional faradaic capacitances at electrode/electrolyte interface. A hybrid supercapacitor (HSC) fabricated effectively utilizes these faradaic capacitances across an extended potential window of 1.2 V in a 2 M H2SO4 solution, yielding impressive capacitance values of 110.4 F/g at a current density of 1 A/g. Furthermore, our synthesis strategy could effectively anchor POMs resulting in a high capacitive retention of 92.4% at high scan rates of 50 mV/s after 5000 cycles. Our approach can be effective in designing POM based pseudo capacitive electrodes with excellent structural stability and surface properties that can be relevant to many electronic and energy applications.

Linearly Scanning Spoof Surface Plasmon Polaritons Leaky-Wave Antenna With High Scanning Rate

Linearly Scanning Spoof Surface Plasmon Polaritons Leaky-Wave Antenna With High Scanning Rate

Understanding the Anomalous J–V Curves in Carbon‐Based Perovskite Solar Cells as a Structural Transition Induced by Ion Diffusion

The investigation of hole transport layer‐free mesoporous carbon perovskite solar cells by analyzing current–voltage (J–V) curves under different scan rates, light intensities, and temperatures is presented. A distinctive bump in the curves is identified, previously reported in the literature. The voltage at the inflection point of this transition shows a linear correlation with the scan rate, directly yielding a characteristic relaxation time. Increasing temperature demonstrates a reduction in the magnitude and characteristic time of the bump. It also indicates an activation energy of 0.8 eV, suggesting a diffusion mechanism. Importantly, the intensity of the illumination has no influence on the overall behavior, indicating that the phenomenon is not a photovoltaic processes. It is proposed that the bump originates from transition between a metastable state at high scan rates and a stable one reached after relaxation. To accurately replicate the measured J–V curves, a novel lumped circuit model is introduced and validated. A schematic microstructural model depicts the reversible reduction in photocurrent as a decline in charge transfer capacity caused by the diffusion of large ions at the mesoporous titanuim dioxyde interface. Ultimately, this study also suggests a plausible reason for the well‐known hysteresis commonly observed with perovskite solar cells.

High‐rate metal‐free MXene microsupercapacitors on paper substrates

AbstractMXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors (MSCs). Despite its superior electrochemical performance, only a few studies have reported MXene‐based ultrahigh‐rate (>1000 mV s−1) on‐paper MSCs, mainly due to the reduced electrical conductance of MXene films deposited on paper. Herein, ultrahigh‐rate metal‐free on‐paper MSCs based on heterogeneous MXene/poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS)‐stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing. With a footprint area of only 20 mm2, the on‐paper MSCs exhibit excellent high‐rate capacitive behavior with an areal capacitance of 5.7 mF cm−2 and long cycle life (>95% capacitance retention after 10,000 cycles) at a high scan rate of 1000 mV s−1, outperforming most of the present on‐paper MSCs. Furthermore, the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal‐free on‐paper MSC arrays, which can also be simultaneously charged/discharged at 1000 mV s−1, showing scalable capacitive performance. The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on‐paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics.

High Scanning Rate Millimeter Wave Circularly Polarized CTS Leaky-Wave Antenna

High Scanning Rate Millimeter Wave Circularly Polarized CTS Leaky-Wave Antenna

Antimony vanadate spheres: Synthesis, characterizations, and use as positive electrode in asymmetric supercapacitor systems

A straightforward wet chemical technique was employed to design and synthesize microstructured SbVO4, and its structural and surface morphological properties were examined using various analytical techniques. The electrochemical performance of SbVO4 NPs was studied using chronopotentiometry, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrode exhibits a specific capacitance (Csp) of 384 Fg−1 at 5 mVs−1, showcasing rapid Faradic redox reactions and efficient charge transfer even at higher scan rates. The relationship between scan rates, Csp, and current densities reveals promising kinetics, with the Csp increasing as the scan rate decreases. The SbVO4 electrode maintains a high capacitance retention of 91 % after 6000 GCD cycles, highlighting exceptional cycling stability. The SbVO4//AC asymmetric device, constructed to assess practicality, displays distinct CV profiles and remarkable reversibility at various scan rates. The device achieves a Csp of 62 Fg−1 at 1 Ag−1, with 84 % capacitance retention after 5000 GCD cycles. A Ragone plot illustrates the device's energy density of 22.04 Whkg−1 and power density of 793.4 Wkg−1, affirming the effectiveness of SbVO4//AC as a robust electrode material for SCs in practical applications.

Understanding the High Scan Rate PDP Curves Obtained By Seccm

Scanning electrochemical cell microscopy (SECCM) is progressively employed for investigating corrosion behaviors at localized sites on metal surfaces. Normally, hundreds of potentiodynamic polarization (PDP) measurements are conducted on the sample using a high potential scan rate to reduce the experimental duration. However, polarization curves obtained under such conditions would yield inaccurate Tafel kinetics. In this research, we performed PDP measurements on Al sample at various scan rates using SECCM and obtained reproducible results. The experimental polarization curves were successfully simulated by a high field model that accounted for the cathodic contribution from oxygen reduction reaction and the anodic contribution from Al oxide film growth. By utilizing this model, we were able to extract the true corrosion kinetic properties from the high scan rate polarization curves, which has not been reported previously. This study represents a significant contribution towards enhancing SECCM-based micro-polarization as a robust quantitative technique for corrosion study.

Use of Surface Features with Controlled Kinetics to Verify Fits of Scanning Electrochemical Microscopy Images

Scanning Electrochemical Microscopy (SECM) is a promising technique for measuring kinetics of redox reactions at surfaces. The conversion of the current map - produced by rastering an electrode over the surface - to a maps of the rate constant of reactions at the surface requires computer modelling and statistical techniques. Experimentally obtained SECM images are necessary to validate computer models that will be used to test these fitting procedures.The largest challenge was finding or creating samples that have reactive sites of known kinetics that were sufficiently slow to be activation-limited. This was achieved by producing small precious metal electrodes embedded in an insulating surface. The exchange currents of these electrodes were characterized using cyclic voltammetry at high scan rates[1,2] so that the rate constant of the electrodes could be effectively controlled by the potential at which they were poised. SECM images of these electrodes can compared to computer simulations to verify that they produced correct results. [1] Nicholson, R.S. Theory and Application of Cyclic Voltammetry for Measurement of Electrode Reaction Kinetics. Anal. Chem. 1965, 37, 11, 1351–1355[2] Mirkin, M.V.; Bard, A.J. Simple Analysis of Quasi-Reversible Steady-State Voltammograms. Anal. Chem. 1992, 64, 19, 2293–2302

Electrochemistry at the Edge of a van der Waals Heterostructure.

Artificial van der Waals heterostructures, obtained by stacking two-dimensional (2D) materials, represent a novel platform for investigating physicochemical phenomena and applications. Here, the electrochemistry at the one-dimensional (1D) edge of a graphene sheet, sandwiched between two hexagonal boron nitride (hBN) flakes, is reported. When such an hBN/graphene/hBN heterostructure is immersed in a solution, the basal plane of graphene is encapsulated by hBN, and the graphene edge is exclusively available in the solution. This forms an electrochemical nanoelectrode, enabling the investigation of electron transfer using several redox probes, e.g., ferrocene(di)methanol, hexaammineruthenium, methylene blue, dopamine and ferrocyanide. The low capacitance of the van der Waals edge electrode facilitates cyclic voltammetry at very high scan rates (up to 1000Vs-1), allowing voltammetric detection of redox species down to micromolar concentrations with sub-second time resolution. The nanoband nature of the edge electrode allows operation in water without added electrolyte. Finally, two adjacent edge electrodes are realized in a redox-cycling format. All the above-mentioned phenomena can be investigated at the edge, demonstrating that nanoscale electrochemistry is a new application avenue for van der Waals heterostructures. Such an edge electrode will be useful for studying electron transfer mechanisms and the detection of analyte species in ultralow sample volumes.

Improved circuitry and post-processing for interleaved fast-scan cyclic voltammetry and electrophysiology measurements

The combination of electrophysiology and electrochemistry acquisition methods using a single carbon fiber microelectrode (CFM) in the brain has enabled more extensive analysis of neurochemical release, neural activity, and animal behavior. Predominantly, analog CMOS (Complementary Metal Oxide Semiconductor) switches are used for these interleaved applications to alternate the CFM output between electrophysiology and electrochemistry acquisition circuitry. However, one underlying issue with analog CMOS switches is the introduction of transient voltage artifacts in recorded electrophysiology signals resulting from CMOS charge injection. These injected artifacts attenuate electrophysiology data and delay reliable signal observation after every switch actuation from electrochemistry acquisition. Previously published attempts at interleaved electrophysiology and electrochemistry were able to recover reliable electrophysiology data within approximately 10–50 ms after switch actuation by employing various high-pass filtering methods to mitigate the observed voltage artifacts. However, high-pass filtering of this nature also attenuates valuable portions of the local-field potential (LFP) frequency range, thus limiting the extent of network-level insights that can be derived from in vivo measurements. This paper proposes a solution to overcome the limitation of charge injection artifacts that affect electrophysiological data while preserving important lower-frequency LFP bands. A voltage follower operational amplifier was integrated before the CMOS switch to increase current flow to the switch and dissipate any injected charge. This hardware addition resulted in a 16.98% decrease in electrophysiology acquisition delay compared to circuitry without a voltage follower. Additionally, single-term exponential modeling was implemented in post-processing to characterize and subtract remaining transient voltage artifacts in recorded electrophysiology data. As a result, electrophysiology data was reliably recovered 3.26 ± 0.22 ms after the beginning of the acquisition period (a 60% decrease from previous studies), while also minimizing LFP attenuation. Through these advancements, coupled electrophysiology and electrochemistry measurements can be conducted at higher scan rates while retaining data integrity for a more comprehensive analysis of neural activity and neurochemical release.

Towards the Enhanced Lithium‐Ion Batteries by Designing (N, Co, Zr, P) Tetra‐Doped Porous Carbon Anode

AbstractHeteroatom‐doped porous carbons have stable structures, high electron/ion transport efficiencies, and rich electroactive sites, which are of great significance to energy storage devices. The potential synergistic effects arising from the multi‐element doping benefit to improve the electrochemical behavior of porous carbon. In this paper, a facile doping strategy has been proposed to prepare the (N, Co, Zr, P) tetra‐doped porous carbon spheres (PCS) for enhanced lithium‐ion batteries (LIBs). The metal‐organophosphine framework (MOPF) as precursor is synthesized by utilizing riboflavin sodium phosphate as organic ligand coordinating with cobalt and zirconium ions. Through carbonizing MOPF, the (N, Co, Zr, P) tetra‐doped PCS can be obtained. As the anode for LIBs, the (N, Co, Zr, P) tetra‐doped PCS exhibits highly reversible capacity of 761 mAh g−1 at 0.1 A g−1 after 100 cycles, excellent rate performance of 126 mAh g−1 even at a high current density of 2 A g−1. The results feature that the unique 3D structure and superior local electron transport properties of (N, Co, Zr, P) tetra‐doped PCS promote the Li+ diffusion and adsorption, which improve the electrochemical properties. Moreover, the mechanism analysis realizes that the Li+ storage of (N, Co, Zr, P) tetra‐doped PCS is determined by the capacitive behavior at high scan rate, highlighting the significance of the heteroatom doping. Therefore, the (N, Co, Zr, P) tetra‐doped PCS should be considered as prominent candidate for high‐performance LIBs anodes.

Electrogeneration of N-substituted polyaniline micro/nanoparticles with potential for energy storage

In the pursuit to develop functionalized polyaniline (PANI) micro/nanoparticles suitable for electrical charge storage, the electrochemical copolymerization of N-(3-sulfopropyl) aniline (AnPS) and N-(2-hydroxyethyl) aniline (AnEtOH) was performed to generate electroactive N-substituted PANI layers directly deposited onto conductive substrates. A particular attention was focused on the impact of the comonomer's molar ratio and pH of the electrolysis solutions on the morphology and electrochemical properties of PANI electrodeposited layers. Thus, four mixtures of the monomers were subjected to electrochemical polymerization in two electrolyte solutions (1 M H2SO4 and acetate buffer solution, pH 4.5) that led to green, homogeneous copolymer deposition layers on the electrode surface. These provided different structural morphologies, that varied from spherical microparticles generated from solution with slightly acidic pH (4.5) to dense, granular morphological features in the case of the deposition layers electrogenerated from 1 M H2SO4. These were characterized in detail by FT-IR and UV–Vis spectroscopies, which confirmed their proposed chemical structure. The electrooxidative polymerization mechanism of the studied N-substituted aniline monomers was evidenced by spectroelectrochemical studies, which highlighted the influence of the monomer's molar ratio and solutions’ pH on the electrolysis process. Moreover, it was demonstrated that the particle dimensions and distributions can be controlled by the comonomer's molar ratio and electrolysis parameters. Considering that the high specific surface area of the obtained PANI micro/nanoparticles can contribute to a better wettability of the polymer molecules with electrolyte ions and their diffusion, the capacitive behaviour of these PANI films was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The highest areal specific capacitance, of 5.32 mFcm−2, was obtained for the polymer electrogenerated from 1:1 molar ratio of the two monomers, that distinguished by the related polymers through a better ion diffusion at low scan rates and efficient charge transfer at high scan rates.

Ag/Ag2O electrode for electrocatalytic oxidation of ethanol

A film of silver oxide is grown on an Ag electrode in KOH solutions, by repetitive cyclic voltammograms at a high scan rate of 2500 mV/s. The formed film is used for the electro-oxidation of ethanol in a dilute potassium hydroxide using the cyclic voltammetry technique. Some effective experimental parameters such as the ethanol concentration, KOH concentration, scanning rate, and temperature on the electrocatalytic oxidation of ethanol have been investigated and discussed. The data confirmed that the formed silver oxide electrode behaves as a good catalyst for the electrooxidation of ethanol. The mechanism of oxidation is likely to be dissociative chemisorption involving one electron transfer. The apparent activation energy, E*, for the electrooxidation, was found to be 68.23 kJ/mole, which is considered too high for a pure diffusion process and moderate for a pure adsorption process. Then the charge transfer is probably controlled by a mixed adsorption-diffusion process

A high-eigenfrequency differential stiffness probe for high-speed scanning probe microscopy

Microcantilever probes used for high-speed scanning probe microscopy are typically required to satisfy two mutually contradicting objectives: high eigenfrequency ( ω n ) and low flexural rigidity ( k b ). The conventional design approach shortens the microcantilever’s length to increase the eigenfrequencies (as ω n ∝ 1 / L 2 ); however, this also increases the probe’s rigidity (as k b ∝ 1 / L 3 ). This paper demonstrates—through experiments and physical modelling—the design of a novel high-eigenfrequency probe by redistributing the microcantilever’s mass along its length. A 100% increase in the probe’s eigenfrequency is achieved with this modified design, even while reducing its stiffness by 50%. Through experiments, this reduced stiffness has been found to enhance the probe’s force sensitivity . Also, the probe’s design facilitates redistributing the fluid pressure between its underside surface and the sample, thereby improving the quality factor by more than 100%. Significant reduction in ‘overshoot’ and ‘parachute’ is observed in contact mode scanning at the video rate. The improvements in the image resolution are proven for a variety of sample surfaces at very high scan rates up to 40 Hz (corresponding to a linear speed of 3.20 mm s − 1 ) upon scanning over an area of 40 × 40 μ m and are successfully demonstrated to map topographies with negligible image artefacts.

Plant-inspired rearrangement of liquid in a porous structure for controlled swelling

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10 μm membrane thickness) assessment of the dynamic variation of PFR in a 400 μm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%–75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s−1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.