Effect of the PH2O/PCO2 and PH2 on the intrinsic electro-catalytic interactions and the CO production pathway on Ni/GDC during solid oxide H2O/CO2 co-electrolysis

•Competitive adsorption and electro-reduction between H2O and CO2 affect the processes.•H2O/CO2 co-electrolysis is determined by the: (i) PH2O/PCO2, (ii) PH2 and (iii) Temp.•By increasing the operating temperature, the electrochemical performance is enhanced.•PH2O/PCO2 = 1 and high PH2 = 21 kPa favor H2O electrolysis, while CO stems from RWGS.•CO2 electrochemical reduction is enhanced at PΗ2Ο/PCO2 < 1 and low PΗ2 = 2 kPa.