Where, 𝐴 is the frequency factor, 𝐸 𝑎 is the activation energy, R is the ideal gas constant and 𝑇 is the absolute temperature of the catalyst. Thus, theoretically, the rate constant 𝑘 for a fixed reaction can be enhanced by either the reduction of 𝐸 𝑎 (i.e. hot carrier mediated route) or by increasing 𝑇 (i.e. photothermal route), or by a combination of both. Both the pathways are active in plasmonic photocatalysis. Herran et al. showed that under 1100 W m -2 intensity broadband illumination, the activation energy is reduced from 33.4 kJ mol -1 to 29.8 kJ mol -1 (i.e. hot carrier mediated) at 25 o C. The heat transfer analysis in Figure shows that for a very small spot size of 1.22 cm in diameter (quartz window for illumination) in Heran et al.'s experiment, the temperature rise of the nanoparticles is very small (<1 o C) due to little thermal accumulation. With a cooling system running , the catalyst temperature certainly remains constant during illumination and the enhancement is entirely hot carrier driven. As shown in Figure (a), this hot carrier driven reduction of Ea by illumination results in 330% (or ~4 times) increase in k over dark conditions. In parallel, Figure shows that it is required to raise the temperature by ~37 o C to achieve the same increase in k via the thermal route. Based on the heat-transfer analysis, more than 25 sun intensity would be required to achieve this temperature rise in Herran et al.'s set-up with normal insulation practices. With 1 sun intensity, an illuminated catalyst film larger than 12 cm x 12 cm would be required to achieve such temperature rise. Thus, rate enhancement with the thermalization of 100% of the absorbed power is possible, but it is energetically totally inefficient. Now, the important question here is, how much of the total absorbed energy has been used in hot carrier activity in Herran et al.'s 24 room temperature experiment. At constant temperature, the doubling of the H2 evolution rate upon illumination can only originate from the hot carrier mediated process that reduced the Ea from 33.4 to 29.8 resulting in quadruple increase in k. As shown in Figure (c), the enhancement of the total H2 production in Herran et al. corresponds to a power of 0.0254 mW that goes towards Ea reduction in the system, which is only 0.18% of the light energy absorbed by the Pt nanoparticles. A similar tiny contribution of non-thermal enhancement at 1250 W m -2 irradiation and high reaction temperature of 325 o C has been shown by Geng et al. The extended analysis of Geng et al. also shows that with increasing intensity, the contribution of the hot carrier effect increases, exceeding 50% at 8 suns. However, the overall light effectiveness of the process improves only 50% at the maximum. This is unexpected given the fact that the hot carrier mediated catalytic process is significantly more efficient. This indicates that complex quantum level processes are at play that require further investigation. (c) Energy balance of the antenna-reactor catalytic system of Herran et al. , from irradiated power to thermalized and reacting hot-carriers.