Electrolysis of low-grade and saline surface water

Abstract

Powered by renewable energy sources such as solar, marine, geothermal and wind, generation of storable hydrogen fuel through water electrolysis provides a promising path towards energy sustainability. However, state-of-the-art electrolysis requires support from associated processes such as desalination of water sources, further purification of desalinated water, and transportation of water, which often contribute financial and energy costs. One strategy to avoid these operations is to develop electrolysers that are capable of operating with impure water feeds directly. Here we review recent developments in electrode materials/catalysts for water electrolysis using low-grade and saline water, a significantly more abundant resource worldwide compared to potable water. We address the associated challenges in design of electrolysers, and discuss future potential approaches that may yield highly active and selective materials for water electrolysis in the presence of common impurities such as metal ions, chloride and bio-organisms. Freshwater is likely to become a scarce resource for many communities, with more than 80% of the world's population exposed to high risk levels of water security 1. This has been recognized within the Sustainable Development Goal 6 (SDG 6) on Clean Water and Sanitation 2. At the same time, low-grade and saline water is a largely abundant resource which, used properly, can address SDG 7 on Affordable and Clean Energy as well as SDG 13 on Climate Action. Hydrogen, a storable fuel, can be generated through water electrolysis and it may provide headway towards combating climate change and reaching zero emissions 3 , since the cycle of generation, consumption and regeneration of hydrogen can achieve carbon neutrality. In addition to providing a suitable energy store, hydrogen can be easily distributed and used in industry, households and transport. Hydrogen, and the related fuel cell industry, has the potential to bring positive economic and social impacts to local communities in terms of energy efficiency and job markets; globally the hydrogen market is expected to grow 33% to US$155 billion in 2022 4. However, there are remaining challenges related to the minimization of the cost and integration of hydrogen into daily life, as well as meeting the ultimate hydrogen cost targets of <US$2 kg-1 set by the US Department of Energy 5-7. Commercially available water electrolysers operate with support from ancillary components/equipment 8,9. The high purity water feeds are achieved by incorporating extensive water purification systems into the overall electrolyser design (internal) or via pre-treatment using external

Facet‐dependent Chlorine and Oxygen Evolution Selectivity on RuO2: An Ab initio Atomistic Thermodynamic Study

“…Increasing the pH of the medium results in the increase and decrease of the OER and CER selectivity, respectively . Electrochemical hypochlorite formation (Cl − +2 OH − →OCl − +H 2 O+2e − , E=1.71 V vs RHE) is favored over the CER (2Cl − →Cl 2 +2e − , E=1.36 V vs RHE) in alkaline medium due to the lower pH sensitivity of the latter reaction . Since the difference between the standard potentials for the OER and for the hypochlorite formation is 0.48 V, the OER is thermodynamically favored under alkaline conditions .…”

Industry-applicable, efficient hydrogen evolution reaction through an interface-activated bimetallic electrode with seawater photolysis in alkaline media

“…negligible amount of Clions, making oxidation of chlorine as a major obstacle for the anodic OER process. At lower pH below 3, the free Cl 2 evolution reaction is dominant, whereas, at high pH range (7.5 to 14), due to the high solubility of the Cl 2 in aqueous solution, the major competitive anodic reaction is hypochlorous acid (HOCl) and hypochlorite ions (OCl -) formation along with OER, however rapidly evolved Cl 2 could still be released from the electrolyte 42. To address these concerns over probable Cl 2 evolution or hypochlorous acid/hypochlorite ion formation, we carried out o-tolidine test to examine the presence of hypochlorous acid/hypochlorite ion in the artificial seawater electrolyte as well as gas chromatography (GC) to analyze the gaseous product collected after the seawater electrolysis test using our NiP 2 -Cu NW /Cu f (-) NiFe-LDH/Ni ǁ f (+) electrolyzer.…”

Efficient and stable electrocatalysts for water splitting

“…35 More importantly, since employment of strong acid and alkaline electrolytes certainly consumes more energy and induces a higher operating cost as well as potential damage to water electrolysis devices, utilizing pure distilled water or even seawater as the electrolyte will become a major development in the near future. 36 In this issue, the Janani et al article summarizes the performance of various catalysts for water splitting and details the corresponding mechanisms in all pH ranges. 37…”