  Recent experiments demonstrated that proton transport through graphene
electrodes can be accelerated by over an order of magnitude with low intensity
illumination. Here we show that this photo-effect can be suppressed for a
tuneable fraction of the infrared spectrum by applying a voltage bias. Using
photocurrent measurements and Raman spectroscopy, we show that such fraction
can be selected by tuning the Fermi energy of electrons in graphene with a
bias, a phenomenon controlled by Pauli blocking of photo-excited electrons.
These findings demonstrate a dependence between graphene's electronic and
proton transport properties and provide fundamental insights into molecularly
thin electrode-electrolyte interfaces and their interaction with light.
