Hydrogen is a zero-carbon footprint energy source with high energy density that could be the basis of future energy systems. Membrane-based water electrolysis is one means by which to produce high-purity and sustainable hydrogen. It is important that the scientific community focus on developing electrolytic hydrogen systems which match available energy sources. In this review, various types of water splitting technologies, and membrane selection for electrolyzers, are discussed. We highlight the basic principles, recent studies, and achievements in membrane-based electrolysis for hydrogen production. Previously, the Nafion™ membrane was the gold standard for PEM electrolyzers, but today, cheaper and more effective membranes are favored. In this paper, CuCl–HCl electrolysis and its operating parameters are summarized. Additionally, a summary is presented of hydrogen production by water splitting, including a discussion of the advantages, disadvantages, and efficiencies of the relevant technologies. Nonetheless, the development of cost-effective and efficient hydrogen production technologies requires a significant amount of study, especially in terms of optimizing the operation parameters affecting the hydrogen output. Therefore, herein we address the challenges, prospects, and future trends in this field of research, and make critical suggestions regarding the implementation of comprehensive membrane-based electrolytic systems.

Hydrogen production by membrane water splitting technologies is a sustainable method to synthesize hydrogen and provides an alternative to hydrogen production instead of conventional process of synthesizing hydrogen from steam methane reforming. A hybrid polymer electrolyte membrane electrolyzer operational at working temperature of above 80–200°C is advantageous for faster electrochemical kinetics, higher current exchange density, and more resistance to fuel impurities. Phosphoric acid (PA) doping onto polybenzimidazole (PBI) membrane shows significant improvement in proton conductivities, permeability, and thermal stability. PBI-based electrolyzer is relatively new to the hydrogen production technologies as compared to Nafion-based electrolyzer. However, the high cost of purchasing Nafion membrane and inability to execute electrolysis operational above 90°C has sparked new interest on PBI-based membrane, which is known for its good thermal stability.

This study was conducted to determine indoor PM_2.5 concentration, which was measured at indoor settings in three different Light Rail Transits in Petaling Jaya. The selected locations were LRT Kelana Jaya, LRT Ara Damansara and LRT Glenmarie. This study focused on determining the indoor fine particulate matter (PM_2.5) associated with samples collected from the three LRTs using Model 8532 DustTrak^TM II Aerosol Monitor (DustTrak) at each LRT from 19:00 to 21:00 three times in a month from July till October 2018. Total of 33 mass concentrations were collected and 176 respondents were recorded from questionnaire given with information on health which was adapted from The American Thoracic Society, “Questionnaire ATS-DLD-C WHO (1982)”. Results were analyzed and compared with US Environmental Protection Agencies (EPA) and World Health Organization (WHO) standards and guidelines. LRT Glenmarie (37.64 µg/m³) was determined higher than US EPA (35 µg/m³) and WHO (25 µg/m³). More than 50% of the survey respondents were affected from the respiratory disease. Therefore, it is necessary to improve the ventilation in LRTs in order to provide a healthier indoor environment.