Impact of tar impurities on hydrogen recovery from coke oven gas via solid oxide electrolysis with steam

Coke oven gas (COG), a by-product of the coking process in blast furnace–based steel production, contains high concentrations of hydrogen (55–60 vol%) and methane (23–27 vol%), along with trace impurities such as phenol. This study investigates the impact of phenol (0–100 g m-3) on the co-electrolysis of simulated COG with steam using a commercially available anode-supported solid oxide electrolysis cell. The cell was characterised through open circuit potential measurements, current–voltage (I–V) curves, quadrupole mass spectrometry, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). At phenol concentrations up to 30 g m-3, catalytic steam reforming and water–gas shift (WGS) reactions were affected, though electrochemical performance remained stable. At concentrations above 30 g m-3, increased activation and concentration losses were observed, with current density reductions of 6.8 % in fuel cell mode and 16.7 % in electrolysis mode at 100 g m-3. SEM and EDS analyses indicated that carbon deposition was the primary cause of performance degradation. Increasing the steam content enhanced SMR and WGS reactions, improving hydrogen yield, purity and cell durability. These findings highlight the importance of steam management in mitigating tar-related degradation and optimising hydrogen recovery from industrial waste gases.