Electronic origin of the reorganization energy in interfacial electron transfer

The activation free energy of electron transfer (ET) reactions is governed by a crucial parameter: the reorganization energy. In heterogeneous ET at electrified solid-liquid interfaces, it is presumed that only factors in the electrolyte phase are responsible for determining the reorganization energy. Here, we demonstrate the contribution of the electronic density of states (DOS) of the electrode to the reorganization energy. Using van der Waals assembly of two-dimensional crystals, we tune the DOS of graphene and measure its impact on outer-sphere ET. We find the ensuing variation in ET rate arises from modulation in a reorganization energy associated with image potential localization in the electrode, which is dependent on the DOS. This work establishes a fundamental role of the electrode electronic structure in interfacial charge transfer.