Selective Catalytic Electro-Oxidation of Water with Cobalt Oxide in Ion Impermeable Reduced Graphene Oxide Porous Electrodes

Abstract

The direct electrolysis of seawater is greatly inhibited by the oxidation of Cl– to free chlorine, an undesirable, corrosive byproduct. To suppress the parasitic interference of Cl– and any other ion, we developed a freestanding, electrically conducting, 3D macroporous reduced graphene oxide (rGO) scaffold with cobalt oxide particles selectively deposited on the internal walls of its closed pores (with an average diameter of ∼180 μm). The pore walls act as membranes composed of stacked rGO flakes; the nanochannels between rGO layers (size <1 nm) are permeable to water and gases while preventing the diffusion of dissolved ions such as Cl–. Due to this, the catalytic particles are selectively accessible to water molecules but not to ions, allowing electrolysis to occur without chlorine evolution. The electrodes developed exhibit a stable generation of O2 from simulated seawater at pH 14, reaching a specific current density of up to 25 A g–1 during continuous electrolysis with 89–98% Faradaic efficiency, while chlorine generation is below 6 ppm h–1, the sensitivity limit of the detection method employed. The strategy here proposed can be generalized to build electrodes that are inherently selective thanks to their architecture, with catalytically active particles loaded into closed pores with selective ion transport properties.

Materials Design and System Innovation for Direct and Indirect Seawater Electrolysis

“…However, it is more challenging in acidic media (pH < 3.5) due to a smaller overpotential window (0.180–0.350 V) for making OER favorable (Figure c). Furthermore, OER is kinetically disadvantageous (4e – transfer) compared to CER involving 2e – transfer, leading to a larger overpotential of OER than CER and further decreased potential gap. − Besides, there are also certain concentrations of other anions in seawater, such as Br – and F – . While the high potential (>3 V vs SHE, standard hydrogen electrode) of fluorine evolution reaction (FER) makes it less notable, the bromine evolution reaction (BER, 1.08 V vs SHE) may also compete with OER under acidic conditions. , Therefore, widening the working potential gap between OER and CER is crucial to avoid the production of corrosive and toxic halides during seawater electrolysis. − …”

Distortion-Induced Interfacial Charge Transfer at Single Cobalt Atom Secured on Ordered Intermetallic Surface Enhances Pure Oxygen Production

“…The first transition-metal oxides like Ni-, Co-, and Fe-based oxides are earth-abundant, low-cost, and magnetic, which have shown promising OER activity. , There are doped RuO 2 -based catalysts delivering enhanced OER activity and stability than pristine RuO 2 . Despite Co being an excellent member among TMs showing OER activity, the major concern is its stability. , To overcome this, various approaches include a decreased loading of Co and generating OER-active catalysts.…”

Chromium doping enabled improvement in alkaline seawater oxidation over cobalt carbonate hydroxide nanowire array

“…Cobalt based materials, including oxides, 28,29 phosphides, 30,31 chalcogenides, 32,33 etc., have emerged as promising OER catalysts in seawater due to their abundance, cost-effectiveness, and superior catalytic activity. Among these, cobalt carbonate hydroxide (CoCH) has long been used as a precursor for the synthesis of cobalt oxides, phosphides, and chalcogenides in view of simple synthesis and favorable morphology.…”

“…Cobalt based materials, including oxides, 28,29 phosphides, 30,31 chalcogenides, 32,33 etc. , have emerged as promising OER catalysts in seawater due to their abundance, cost-effectiveness, and superior catalytic activity.…”