Environmental issues make the quest for better and cleaner energy sources a priority. Worldwide, researchers and companies are continuously working on this matter, taking one of two approaches: either finding new energy sources or improving the efficiency of existing ones. Hydrogen is a well-known energy carrier due to its high energy content, but a somewhat elusive one for being a gas with low molecular weight. This review examines the current electrolysis processes for obtaining hydrogen, with an emphasis on alkaline water electrolysis. This process is far from being new, but research shows that there is still plenty of room for improvement. The efficiency of an electrolyzer mainly relates to the overpotential and resistances in the cell. This work shows that the path to better electrolyzer efficiency is through the optimization of the cell components and operating conditions. Following a brief introduction to the thermodynamics and kinetics of water electrolysis, the most recent developments on several parameters (e.g., electrocatalysts, electrolyte composition, separator, interelectrode distance) are highlighted.

The chemical composition of the essential oil of Portuguese myrtle was determined at different developmental stages of the plant: pre-flowering, flowering, unripe and ripe berries. The oil was extracted separately by Clevenger distillation from leaves, branches and berries. The yields vary from 0.33% to 0.74% for leaves, 0.02% to 0.19% for branches, and 0.11% to 0.23% for berries. The highest yields were obtained for the leaves in October, and for the berries in September; branches show similar values in the months of June, July and September, and the samples collected in May and October produced very little amount of oil. Altogether, September seems to be the month with the best yields for the three parts of the plant. The essential oils were analyzed by GC and GC/MS, and a total of thirty five components were identified. The major components were limonene+1,8-cineole [25.9% (berries)–39.5% (leaves)], myrtenyl acetate [6.6% (berries)–24.8% (leaves)], α-pinene [9.7% (berries)–21.5% (leaves)], and linalool [6.2% (leaves)–36.5% (berries)]. Portuguese myrtle belongs to the group of myrtles which are characterized by the presence of myrtenyl acetate as one of the major components.