Gas Crossover Regulation by Porosity-Controlled Glass Sheet Achieves Pure Hydrogen Production by Buffered Water Electrolysis at Neutral pH

A zero-gap silicon membrane with defined pore size and porosity for alkaline electrolysis

Porous separators are a key component in alkaline water electrolyzers and are significant sources of overpotential. In this paper, porous silicon separators were fabricated by etching precise arrays of cylindrical pores into silicon substrates through lithography. Chemical stability of the silicon-based separators is ensured through the deposition of a silicon nitride layer. Platinum or nickel were vapor-deposited directly on the faces of the separator to complete a zero-gap configuration. Separator porosity (ε) was varied by changing the pore diameter and the pore spacing. These well-controlled porous silicon zero gap electrodes (PSi-ZGEs) were used to study the trade-off between separator resistance and gas-crossover at different porosities. It was found that separator resistances comparable to commercially used Zirfon UTP 500 were achieved at much lower ε. Gas crossover remained within the explosive limits for ε ≤ 0.15%. The PSi-ZGEs achieved stable performance at 100 mA cm-2 for 24 hours without significant surface damage in the alkaline electrolyte. In the broad perspective, the current work can pave the path for the development of ionomer-free separators for alkaline water electrolysis which rely on the separator geometry to limit gas-crossover.

High Current Density Oxygen Evolution in Carbonate Buffered Solution Achieved by Active Site Densification and Electrolyte Engineering

High current density reaching 1 A cm^-2 for efficient oxygen evolution reaction (OER) was demonstrated by interactively optimizing electrolyte and electrode at non-extreme pH levels. Careful electrolyte assessment revealed that the state-of-the-art nickel-iron oxide electrocatalyst in alkaline solution maintained its high OER performance with a small Tafel slope in K-carbonate solution at pH 10.5 at 353 K. The OER performance was improved when Cu or Au was introduced into the FeO_x -modified nanostructured Ni electrode as the third element during the preparation of electrode by electrodeposition. The resultant OER achieved 1 A cm^-2 at 1.53 V vs. reversible hydrogen electrode (RHE) stably for 90 h, comparable to those in extreme alkaline conditions. Constant Tafel slopes, apparent activation energy, and the same signatures from operando X-ray absorption spectroscopy among these samples suggested that this improvement seems solely correlated with enhanced electrochemical surface area caused by adding the third element.

Electrolyte Engineering for Oxygen Evolution Reaction Over Non-Noble Metal Electrodes Achieving High Current Density in the Presence of Chloride Ion

Direct seawater electrolysis potentially simplifies the electrolysis process and leads to a decrease in the cost of green hydrogen production. However, impurities present in the seawater, especially chloride ions (Cl- ), cause corrosion of the electrode material, and its oxidation competes with the anodic oxygen evolution reaction (OER). By carefully tuning electrode substrate and electrolyte solutions, the CoFeOx Hy /Ti electrode with high double-layer capacitance actively and stably electro-catalyzed the OER in potassium borate solutions at pH 9.2 in the presence of 0.5 mol kg-1 Cl- . The electrode possesses an active site motif composed of either a Co- or Fe-domain and benefits from an enlarged surface area. Selective OER was demonstrated in Cl- -containing electrolyte solutions at an elevated reaction temperature, stably achieving 500 mA cm-2 at a mere potential of 1.67 V vs. reversible hydrogen electrode (RHE) at 353 K for multiple on-off and long-term testing processes with a faradaic efficiency of unity toward the OER.