Understanding the role of heat transfer between catalysts and substrates is important for enhancing photothermal CO_2 catalysis.Herein,we investigate the effect of different substrates,including silicon wafers,glass slides and copper plates,on the photothermal catalytic performance of commercial Ni catalysts.The highest CO_2 conversion rate and CO selectivity are observed in the catalyst film on the glass substrate,and this can be traced to a reduced catalyst-to-substrate heat transfer that increases the catalyst temperature under illumination.Our study reveals the important role of thermal management between catalysts and substrates in photothermal catalysis and sheds light on reactor design for efficient solar-to-chemical energy conversions.