Decoupled Electrochemical Water Splitting: From Fundamentals to Applications

Abstract

rely on fossil fuels is of great importance. Renewable energy sources, such as wind, solar, and tidal energy constitute arguably the most promising of these clean energy solutions, but suffer from the fact that they are intermittent. [6] Direct power supply from these sources therefore cannot be relied upon to satisfy instantaneous energy demands. [7] A means of storing the energy generated by these renewable sources is therefore essential if we are to depend more heavily on renewably generated power. [8] Hydrogen (H 2) is often proposed in this context as a promising "carbon neutral" energy carrier (i.e., fuel). In such a system, renewably generated electricity is used to electrolyze water to generate hydrogen and oxygen. The oxygen may be vented to the atmosphere whilst the hydrogen is stored as a fuel. This hydrogen is then subsequently oxidized (either by combustion or in a fuel cell) to regenerate water and to release energy. Hydrogen is not a perfect fuel but it does have a number of attractive properties such as its low toxicity, ability to be transported safely over long distances via pipeline, [9] and its high energy density per unit mass (three times greater than that of gasoline). [10] Moreover, sustainably sourced hydrogen could be used to reduce CO 2 or N 2 from the atmosphere to generate carbon-neutral fuels and commodity chemicals such as hydrocarbons and ammonia. In many ways then, hydrogen can be viewed as the key to a sustainable energy cycle. The process of water electrolysis can be considered in terms of its two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). These half-equations differ somewhat depending on the pH at which the electrolysis is carried out. At low pH, the HER and OER proceed as follows (all potentials are vs the standard hydrogen electrode, SHE)

Superaerophobic/superhydrophilic surfaces as advanced electrocatalysts for the hydrogen evolution reaction: a comprehensive review

“…Unlike hydrogen produced from hydrocarbons, EWS can be employed independently for many applications, e.g., fuel cells. [16][17][18] An electrolyzer comprises three parts: an electrolyte, a cathode, and an anode (Fig. 2).…”

Strategies for Electrochemically Sustainable H2 Production in Acid

“…[ 11 ] Importantly, it can be used for energy generation and utilization without the emission of any greenhouse gases. [ 12 , 13 ] Electrochemical water electrolysis for H 2 production has thus attracted extensive research interests. The process normally involves two half reactions: hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode.…”

“…[ 16 ] According to Sabatier's principle, Pt‐based and Ir/Ru‐based electrocatalysts are known to facilitate, with fair stability and excellent activity, acidic HER and OER, respectively. [ 12 , 14 , 15 ] However, these noble metal electrocatalysts are not entirely stable in acidic media. Specifically, IrO 2 suffers from slow dissolution in acidic media, and RuO 2 is even less stable than IrO 2 .…”

“…[ 18 , 19 ] To achieve SHP, current main‐stream studies are focused on tuning the atomic/nano structure of metal electrocatalysts for enhanced stability and activity under acidic OER conditions, with only limited effectiveness. [ 14 , 15 ] Additionally, new reaction control strategies have been investigated (e.g., decoupling/hybridizing/tandem catalyzing strategies), [ 1 , 12 , 20 , 21 ] although the corresponding guiding principles for SHP based on water electrolysis in acidic media have been not summarized. Furthermore, a systems approach that considers operating reactions and electrode and device configurations/operations is still lacking, which is of great significance because it may provide innovative strategies for SHP.…”

An Investigation of a (Vinylbenzyl) Trimethylammonium and N-Vinylimidazole-Substituted Poly (Vinylidene Fluoride-Co-Hexafluoropropylene) Copolymer as an Anion-Exchange Membrane in a Lignin-Oxidising Electrolyser

“…Although this energy requirement can be lowered by employing appropriate electrocatalysts, an intriguing alternative to this is to replace the OER with an anode couple that does not (at least in theory) require such significant overpotentials. To this end, the electrolysis of organic compounds as a route to H 2 production has garnered some interest [20][21][22][23][24]. Provided that the organic substrates that are being oxidised are renewable (e.g., they are derived from plant-based material), then such a system would allow the production of hydrogen from water at lower potentials than the direct electrolysis of water to O 2 and H 2 without adding to the long-term concentration of CO 2 in the atmosphere.…”