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Abstract: We report, for the first time, symmetric (versus cluster potential of zero charge) charging of narrowly dispersed monolayer-protected Au145 cluster films in a room temperature ionic liquid. Near-reversible voltammetric features are found, indicating up to nine electrochemically accessible charge states with assigned values between −4 and +5. The zero charge state has a stability range of 276mV, very similar as found in solution-phase voltammetry. All other charge states are more narrowly spaced, indicating a sudden increase in cluster capacitance. We ascribe this effect to an abrupt change in local dielectric constant on insertion of one or more counter ions, following departure from zero charge, with a possible contribution of coupled electron–ion transfer. Our findings open perspectives of potential technological importance involving nanocrystal-based device-like behaviour. [Copyright &y& Elsevier]

Abstract: We present a simple yet absolute method for the assignment of the zero charge state of metal nanoparticle films during their electrochemical charging. The method is based on measuring the current transient that accompanies the potential controlled immersion of a pristine, ion-free cluster film in an electrolyte, and does not rely on relative quantities such as mass changes of an already immersed film. Therefore, the method is impervious to details of counter ion insertion — for instance whether the electrolyte can partition into the film or not — without which no charging can be observed. Examples of positive and negative ion-limited charging are presented, and an example of ambipolar cluster charging, covering the three possible cases. The immersion method can be readily applied to other cases of coupled electron–ion transfer, as in the three-phase electrochemistry of redox droplets and thin films. [Copyright &y& Elsevier]