A crosslinked polymer membrane kept hydrogen contamination on the oxygen side of an alkaline electrolyzer below 4% by volume during more than 1,900 hours of operation. The peer-reviewed study reports that the contamination rose nearly four times more slowly than with the uncrosslinked membrane. The result addresses a practical failure mode: a separator can continue conducting ions while chemical damage gradually lets hydrogen cross into the oxygen stream.
The cell uses an ion-solvating membrane made from polybenzimidazole, or PBI. Rather than attaching permanent charged groups to the polymer, the film absorbs potassium hydroxide solution. That liquid supplies hydroxide ions for the electrolysis reaction. The design can work with concentrated alkaline electrolyte and electrodes that do not contain platinum-group metals, but ordinary PBI can thin as the polymer chains degrade. A thinner film lowers electrical resistance while also giving hydrogen a shorter path across the cell.
The researchers reinforced the film with a benzoxazine crosslinker. Heating opens the crosslinker's ring and builds a network through the aromatic parts of the PBI, leaving the polymer's nitrogen-hydrogen sites available to hold alkaline solution. The added network resisted dissolution in four organic solvents, while the original PBI dissolved in two of them. Crosslinking also disrupted tightly packed chains, creating room for water and potassium hydroxide. This matters because too little uptake would slow hydroxide transport, while excessive swelling would make gas separation worse.
The balance appeared at 20% crosslinker by weight. Before alkaline soaking, that film was 35 micrometres thick. In 10% potassium hydroxide at 60 degrees Celsius, its ionic conductivity, a measure of how readily ions move through the membrane, reached 94.3 millisiemens per centimetre, compared with 51.4 for the original PBI. During cell tests from 0.3 to 1.2 amperes per square centimetre, hydrogen in the oxygen stream stayed below 1%. A film with 40% crosslinker crossed that threshold throughout the tested current range, showing that more crosslinking did not automatically improve gas control.
The long run used the 20% film. Hydrogen crossover remained below 4% for more than 1,900 hours, and the paper attributes the slower rise to reduced membrane thinning. The evidence also shows where degradation has not disappeared. After 3,200 hours of separate alkaline exposure, infrared spectra developed bands consistent with possible cleavage in the crosslinking network and chemical attack on the PBI backbone. The authors describe these signals cautiously because they indicate likely degradation products rather than mapping the network atom by atom.
Under these test conditions, crosslinking slowed membrane thinning while maintaining ion conduction. It does not yet establish stack-scale life: the work used laboratory films, one alkaline concentration and controlled temperatures, without pressurized gas separation, renewable-power cycling, manufacturing-yield data or a cost comparison.