Coupling Ferrocyanide-Assisted PW/PB Redox with Efficient Direct Seawater Electrolysis for Hydrogen Production

Abstract

Direct seawater electrolysis is a promising approach for grid-scale hydrogen mass production. However, the low energy efficiency and detrimental anodic chlorine electrochemistry unlock its practical potential. Here, we present an efficient chlorine-free hydrogen production by coupling the rapid electrode reaction of ferrocyanide-assisted Prussian white (PW)/Prussian blue (PB) redox with an onset potential of 0.87 V RHE . The chloride oxidation in our cells is avoided by low cell voltages, enabling high-purity hydrogen production. Operando spectroscopic analysis coupled with theoretical calculations validates that the addition of the [Fe(CN) 6 ] 3−/4− redox mediator in the electrolyte can reduce the PB to PW instantaneously, thus completing the cycle of PW/ PB redox and making the system recyclable. The assembled electrolyzer exhibited unprecedented performance for direct seawater electrolysis (pH = 8.5), achieving a current density of 320 mA cm −2 at 1.7 V. Therefore, the electricity consumed per cubic meter of H 2 produced in the electrolyzer is 3.8 kWh at 200 mA cm −2 , and 42% lower energy equivalent input relative to commercial redoxfree seawater electrolysis. This work offers a cost-competitive and energy-saving strategy for producing high-purity H 2 directly from unlimited seawater.

Recent Progress in Design Strategy of Anode for Seawater Electrolysis

“…N 2 þ 4H 2 O þ 4e À , À0.33 V vs RHE), [188] and K 4 Fe 4 [Fe(CN) 6 ] 3 (PW) ! Fe 4 [Fe(CN) 6 ] 3 (PB)þ4 K þ þ 4e À , [189] etc. Coupling HER with these reactions at the anode also gains value-added products or defuse the pollutants, making this designing strategy more advantageous.…”

“…Because the potential windows between COR and these oxidation reactions could be broadened. There are some developed oxidation reactions using different species, including the sulfation oxidation reaction (SOR, S 2− – 2e − → S, −0.48 V vs RHE), [ 186 ] methanol oxidation reaction (MSOR, CH 3 OH + 5OH − → HCOO − + 4H 2 O + 4e − , 0.2–0.25 V vs RHE), [ 187 ] hydrazine oxidation reaction (HzOR, N 2 H 4 + 4OH − → N 2 + 4H 2 O + 4e − , −0.33 V vs RHE), [ 188 ] and K 4 Fe 4 [Fe(CN) 6 ] 3 (PW) → Fe 4 [Fe(CN) 6 ] 3 (PB)+4 K + + 4e − , [ 189 ] etc. Coupling HER with these reactions at the anode also gains value‐added products or defuse the pollutants, making this designing strategy more advantageous.…”

Coupling Ferricyanide/Ferrocyanide Redox Mediated Recycling Spent LiFePO4 with Hydrogen Production

“…has also been proposed as a viable alternative reaction to OER. [14][15][16] The advantage of using electrooxidation of multivalent metals is that it does not require any catalyst to facilitate the reaction and has been intensively investigated in electroplating, secondary ion batteries and other electrochemical fields. [17] Unfortunately, the anodic reaction of multivalent metals encounters the challenge of unsustained electrooxidation.…”

Polarization Manipulation of NiO Nanosheets Engineered with Fe/Pt Single Atoms for High-Performance Electrocatalytic Overall Alkaline Seawater Splitting

“…Utilizing renewable electricity combined with water electrolyzers to produce clean hydrogen affords a promising route to alleviate the energy and environmental issues caused by the increasing consumption of fossil fuels. − The current electrolyte mainly comes from freshwater, while the shortage of freshwater feed may become a bottleneck for large-scale water electrolysis. − Seawater accounts for 96.5% of all available water, and large-scale water electrolysis consequently becomes more engaging in the scenario with abundant seawater resources and solar energy to achieve photovoltaics-driven electrolysis. − The main obstacle to seawater electrolyzers is the competitive active chlorine species formation reactions, which include chlorine evolution reactions at low pH and chlorine oxidation reactions at high pH, resulting in the reduced selectivity of the oxygen evolution reaction (OER) and catalyst deactivation due to chlorine corrosion. − Therefore, developing highly selective and efficient seawater electrocatalysts is essential but still challenging.…”