Operando Temperature Sensing at the Actual Electrocatalytic Interface by Nanodiamond Quantum Sensors

ABSTRACT Operando temperature monitoring with submicron spatial resolution at the actual electrocatalytic reaction interface remains a significant challenge. Here we tackle this issue by adopting nanodiamonds (NDs) quantum sensors in an electrolyzer. We show that by integrating a wide‐field microscope and a specially designed electrolyzer, nanoscale temperature changes can be recorded in operando during electrolysis processes without interfering with the ongoing electrochemistry. The ND sensors detect significantly higher local temperatures at the reaction interface of the working electrolyzer compared to the average temperature measured either in the electrolyte or at the back surface of the electrode using conventional methods like thermocouples or infrared cameras. This discrepancy becomes more pronounced as the current increases. Experimental evidence suggested that the actual temperature at the reaction interface is directly correlated with the specific electrochemical reaction at the surface, serving as an indicator of reactivity. Additionally, thermal mapping of the reaction interface reveals significant spatial temperature non‐uniformity at the nanoscale, indicating varying reactivities at local sites. Consequently, the observed temporal evolution of local temperatures suggests fluctuations in reactivity at these locations. This advanced understanding of nanoscale temperature evolution in a working electrochemical device will ultimately contribute to developing strategies to improve device efficiency and stability, ranging from electrocatalyst design to thermal management.