Unitized regenerative fuel cells operate in not only fuel cell but also water electrolyzer mode. Heat management is important for the stable operation of unitized regenerative fuel cells. In this work, temperature and heat flux on the surface of the gas diffusion layer at the hydrogen side of a unitized regenerative fuel cell are experimentally measured using thin film sensors. Four pairs of sensors with good linear relation coefficient are inserted in the unitized regenerative fuel cell. The variation of temperature and heat flux on the gas diffusion layer surface during mode switching is obtained. The effect of mode switching on temperature and heat flux in the unitized regenerative fuel cell is analyzed. Experimental results show that reactant switching significantly affects temperature and heat flux. Reactant switching also causes decreased temperature and variation in heat flux. Despite of the decrease of temperature caused by the low-temperature water, the temperature increases with the operation of the URFC. When the effect of reactant switching is ignored, temperature is further found to increase in fuel cell and water electrolyzer modes, and heat flux remains relatively stable. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.