Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO₂ footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Root-growing, containable mossy lithium changes to tip-growing, short-causing dendritic lithium at “Sand's capacity”, which is set by electrolyte diffusion limitation.

We develop a simple Landau-Ginzburg-type continuum theory of solvent-free ionic liquids and use it to predict the structure of the electrical double layer. The model captures overscreening from short-range correlations, dominant at small voltages, and steric constraints of finite ion sizes, which prevail at large voltages. Increasing the voltage gradually suppresses overscreening in favor of the crowding of counterions in a condensed inner layer near the electrode. This prediction, the ion profiles, and the capacitance-voltage dependence are consistent with recent computer simulations and experiments on room-temperature ionic liquids, using a correlation length of order the ion size.

The response of a model microelectrochemical system to a time-dependent applied voltage is analyzed. The article begins with a fresh historical review including electrochemistry, colloidal science, and microfluidics. The model problem consists of a symmetric binary electrolyte between parallel-plate blocking electrodes, which suddenly apply a voltage. Compact Stern layers on the electrodes are also taken into account. The Nernst-Planck-Poisson equations are first linearized and solved by Laplace transforms for small voltages, and numerical solutions are obtained for large voltages. The “weakly nonlinear” limit of thin double layers is then analyzed by matched asymptotic expansions in the small parameter $\epsilon ={\lambda }_D∕L$, where ${\lambda }_D$ is the screening length and $L$ the electrode separation. At leading order, the system initially behaves like an $RC$ circuit with a response time of ${\lambda }_{D}L∕D$ (not ${\lambda }_D^2∕D$), where $D$ is the ionic diffusivity, but nonlinearity violates this common picture and introduces multiple time scales. The charging process slows down, and neutral-salt adsorption by the diffuse part of the double layer couples to bulk diffusion at the time scale, $L^2∕D$. In the “strongly nonlinear” regime (controlled by a dimensionless parameter resembling the Dukhin number), this effect produces bulk concentration gradients, and, at very large voltages, transient space charge. The article concludes with an overview of more general situations involving surface conduction, multicomponent electrolytes, and Faradaic processes.

The ascorbate oxidase (AsOx) immobilized onto sol gel derived nanostructured ZrO₂ film deposited onto indium tin oxide (ITO) glass has been employed for vitamin C detection. The AsOx/NanoZrO₂/ITO bioelectrode characterized using spectroscopic and electrochemical techniques reveals response time of 15 s, sensitivity of 0.815 mA/mg dl cm², detection limit of 20 mg dl⁻¹, an apparent K_m value of 19.50 mg dl⁻¹ and can be used to estimate vitamin C concentration up to 500 mg dl⁻¹. This bioelectrode is thermally stable up to 40°C and has a shelf-life of about 6 weeks when stored at 4°C. These results, combined with its structure compatibility with a wide range of biofunctionalization procedures, would make the AsOx/NanoZrO₂/ITO biosensor exceptionally useful for a range of detection schemes for clinically important biomarkers.