The visualization of the microstructure change and of the depth of lithium transport inside a monolithic ElectroChromic Device (ECD) is realized using an innovative combined approach of Focused Ion Beam (FIB), Secondary Ion Mass Spectrometry (SIMS) and Glow Discharge Optical Emission Spectroscopy (GDOES). The electrochemical and optical properties of the all-thin-film inorganic ECD glass/ITO/WO₃/LiTaO₃/NiO/ITO, deposited by magnetron sputtering, are measured by cycling voltammetry and in situ transmittance analysis up to 11 270 cycles. A significant degradation corresponding to a decrease in the capacity of 71% after 2500 cycles and of 94% after 11 270 cycles is reported. The depth resolved microstructure evolution within the device, investigated by cross-sectional cutting with FIB, points out a progressive densification of the NiO layer upon cycling. The existence of irreversible Li ion trapping in NiO is illustrated through the comparison of the compositional distribution of the device after various cycles 0, 100, 1000, 5000 and 11 270. SIMS and GDOES depth profiles confirm an increase in the trapped Li content in NiO as the number of cycles increases. Therefore, the combination of lithium trapping and apparent morphological densification evolution in NiO is believed to account for the degradation of the ECD properties upon long term cycling of the ECD.

There has been keen interest for years in the research of all-solid-state transmittance-type electrochromic (EC) devices due to their various applications especially in “smart windows”. A step forward has been taken in the successful preparation of full multilayered devices with enlarged optical contrast and fast switching response. However, limited durability remains a severe issue. Upon cycling, EC devices suffer from decline of charge capacity as well as optical modulation while the detailed degradation mechanisms remain poorly understood. Here, we demonstrate unambiguous ion-trapping evidence to interpret the charge density decay of the EC device induced using various voltammetric cycling protocols, namely long-term cycling and accelerated cycling. Pronounced comparable ion trapping occurs in cathodically colored WO₃ films whatever the cycling procedure is, suggesting the existence of the trapping “saturation” phenomenon. From second-ion-mass-spectroscopy analysis, the ⁷Li⁺/¹⁸⁴W⁺ ratio in the degraded WO₃ films is more than 100 while it is almost zero in the as-prepared films. In contrast, for anodically colored NiO, a larger number of trapped cations is determined in the long-term cycled films than in the accelerated ones. In combination with X-ray-photoelectron-spectroscopy, variable bonding energies indicate that the ions are trapped at different types of sites, depending on the cycling procedure, and they can reside in the structural channels or break the network chains to form new chemical bondings, thus resulting in a significant color difference. In addition, a clear upward trend in the trapped Li concentration along with depth is observed. All our findings provide a deep insight into the degradation phenomenon taking place in electrochromic films as well as in full devices and offer valuable information for the understanding of micro mechanisms.

Knowledge of transduction mechanisms in biosensing applications paves the way for ultrasensitive and dynamic detection in living systems. Real-world biosensing applications where ultra-sensitivity and dynamic detection are paramount include monitoring the anesthetic agent concentration during surgery; the slightest variation in concentration can potentially result in a life-threatening overdose or, on the other end of the spectrum, the patient’s awareness during the procedure. We review the benefits and functions of the transcutaneous biosensor device compared with other current technology and discuss the sensor’s capability to accurately measure volatile anesthetic gas concentration in blood using fuel cell technology. We review fundamental concepts of fuel-cell technology for wearable bio-sensing applications. The fuel cell sensor can also continuously monitor other volatile organic compounds making it versatile with numerous potential applications.

To the best of our knowledge, very few works have been done for the continuous real-time monitoring of Proton Exchange Membrane Fuel Cells (PEMFCs) membrane degradation based on fluoride-specific electrochemical microsensors. PEMFCs are eco-smart energy sources for efficient transportation but experience variable degradation rates that wear the Membrane Electrode Assembly (MEA), a critical component of the fuel cell’s functionality. Current market options lack specific diagnostics and a legitimate indication of when exactly the membrane needs to be replaced. As such, this work focused on manufacturing a sensor for measuring MEA degradation in real-time by selectively monitoring fluoride concentration in effluent water, a signature PEMFCs degradation status, through functionalized LaF₃:(Au nanoparticle) thin films (∼60 nm). The sensor’s exceptional specificity/sensitivity has been achieved in real-time at a sub 10 ppb level, optimized through spin-coating deposition and post-annealing process. Its multimodal readout has been achieved and studied through the characterizations of open circuit potential, cyclic voltammetry, chronoamperometry, and differential pulse voltammetry revealing a consistent linear decrease of 15.7 mA cm⁻² at 0 ppb to 10.2 mA cm⁻², while also maintaining its low-cost, small size, and robustness.

Electrochromic pseudocapacitive transition-metal oxide materials, such as tungsten oxide, which combine fast response, high energy density, and optical effects, can play a significant role as energy storage materials. Here we investigate the electrochemical kinetics of thin films of tungsten oxide, which turn transparent to sky-blue color in the lithiated state due to the reduction of W ⁶⁺ to W ⁵⁺ . We investigated the charge density, charge transfer, ion diffusion, and interfacial behavior upon Li ⁺ insertion/de-insertion in WO ₃ . The electrochromic thin film’s pseudocapacitive and electrical double layer mechanism was differentiated based on the power-law. Faradaic diffusion-controlled process dominates over the surface capacitive behavior at scan rates below 40 mV s ⁻¹ . These films exhibit an areal charge density of around 100 mC cm ⁻² and a capacitance of 80 mF cm ⁻² , superior to most comparable electrochromic materials and supercapacitors. This work combines electrochromics and energy storage properties and provides a fundamental understanding of pseudocapacitive and electrochromic mechanisms in WO ₃ .

Recently, progress in electrochromic (EC) devices has been made in optimizing electrode and device configurations and performance. However, the ion insertion/de-insertion induced charge transfer (CT) nanomechanical effect has remained unexplored, i.e., repetitive electrode size changes at the nanoscale and stress/strain generated during electrochemical cycling, which is the focus of this work due to its intimate correlation with the elastic and plastic deformation at the interface. Considering the intervalence electrons, excellent electrochemical kinetics, and dramatic color changes, tungsten oxide (WO₃) and nickel oxide (NiO) films are configured as the EC cathode and anode materials, respectively, within a full device. Upon extended cycles (>10 000), the void generation and delamination that occurred at the interface account for performance decay. Encouraged by the findings, nanoindentation mechanical tests and electrical kelvin probe force microscopy were employed to investigate the CT induced effects at the interface. There is a dramatic increase of up to 45% in the elastic Young's modulus in colored/charged WO₃ at ∼40 mC cm⁻². The correlation between CT and synergistic mechanical effect is interpreted by the Lippman equation. Interestingly, despite the charged state (colored; lithiated) with a relatively flat morphology bringing an ∼3.4 times higher electrostatic surface potential, the electrical work function unexpectedly decreases, arising from the dominant effect of the dipole layer potential over the chemical potential. The interatomic cohesive energy and equilibrium distance increase bury the seeds for mechanical deformation in the long run. This work provides fundamental insights into electro-chemo mechanics and interdisciplinary concerted interfacial effects at the nano/atomic level. The dependence of surface potential, stress, work function, and cohesive energy on electrochemical kinetics has been interpreted.