To the best of our knowledge, very few works have been done on 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 legitimate indication of when exactly the membrane must 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/cm2 at 0 ppb to 10.2 mA/cm2, 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 turns transparent to sky-blue in color in the lithiated state due to the reduction of W6+ to W5+. We investigated the charge density, charge transfer, ion diffusion, and interfacial behavior upon Li+ insertion/de-insertion in WO3. The pseudocapacitive and electrical double layer mechanism of the electrochromic thin film was differentiated based on the power-law. Faradaic diffusion-controlled process dominates over the surface capacitive behavior at scan rates below 40 mV/s. These films exhibit areal charge density of around 100 mC/cm2 and a capacitance of 80 mF/cm2, which are superior to most comparable electrochromic materials and supercapacitors. This work reports combining electrochromics and energy storage properties and provides a fundamental understanding of pseudocapacitive and electrochromic mechanisms in WO3.

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