Activation Energies of Plasmonic Catalysts

The
activation energy of a catalytic reaction serves not only as a metric
of the efficacy of a catalyst but also as a potential indicator of
mechanistic differences between the catalytic and noncatalytic reaction.
However, activation energies are quite underutilized in the field
of photocatalysis. We characterize in detail the effect of visible
light excitation on the activation enthalpy of an electron transfer
reaction photocatalyzed by plasmonic Au nanoparticles. We find that
in the presence of visible light photoexcitation, the activation enthalpy
of the Au nanoparticle-catalyzed electron transfer reaction is significantly
reduced. The reduction in the activation enthalpy depends on the excitation
wavelength, the incident laser power, and the strength of a hole scavenger.
On the basis of these results, we argue that the activation enthalpy
reduction is directly related to the photoelectrochemical potential
built-up on the Au nanoparticle under steady-state light excitation,
analogous to electrochemical activation. Under optimum light excitation
conditions, a potential as high as 240 mV is measured. The findings
constitute more precise insights into the mechanistic role and energetic
contribution of plasmonic excitation to chemical reactions catalyzed
by transition metal nanoparticles.