This paper reports an experimental study on the effects of reactor geometry for dissociating carbon dioxide using a microhollow cathode discharge (MHCD) reactor, and the associated electrode degradation. A MHCD reactor consists of two hollow metal electrodes that are separated by dielectric material. The geometric reactor parameters studied were the dielectric material thickness and the diameter of the reactor hole. Dielectric thicknesses of 150, 300 and 450 mu m and discharge hole diameters of 200, 400 and 515 mu m were studied parametrically. The results of each parameter combination were discussed in terms of specific energy input (SEI), CO2 conversion, electrical-to-chemical energy conversion efficiency, and degradation rate of the electrodes. Overall, the results showed that, at constant SEI, increasing the dielectric thickness increased CO2 conversion and energy efficiency but decreased the degradation rate. Moreover, at a constant SEI, varying the hole diameter did not affect CO2 conversion or efficiency but the electrode degradation rate decreased with increasing hole diameter. The maximum efficiency observed was about 18.5% for the dielectric thickness of 450 mu m, hole diameter of 400 mu m, and a SEI of 0.1 eV/mol. With this reactor geometry, the maximum CO2 conversion was 17.3% at a SEI of 3.7 eV/mol. Moreover, the results showed that the rate of electrode degradation increased linearly with time at a rate ranging from 130 to 207 mu m(2)/s, with a reactor lifetime of 13 hours at a SEI of 3.7 eV/mol. (C) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.