  Strong electric fields can accelerate molecular dissociation reactions. The
phenomenon known as the Wien effect was previously observed using high-voltage
electrolysis cells that produced fields of about 10^7 V m-1, sufficient to
accelerate the dissociation of weakly bound molecules (e.g., organics and weak
electrolytes). The observation of the Wien effect for the common case of water
dissociation (H2O = H+ + OH-) has remained elusive. Here we study the
dissociation of interfacial water adjacent to proton-permeable graphene
electrodes and observe strong acceleration of the reaction in fields reaching
above 10^8 V m-1. The use of graphene electrodes allow measuring the proton
currents arising exclusively from the dissociation of interfacial water, while
the electric field driving the reaction is monitored through the carrier
density induced in graphene by the same field. The observed exponential
increase in proton currents is in quantitative agreement with Onsager's theory.
Our results also demonstrate that graphene electrodes can be valuable for the
investigation of various interfacial phenomena involving proton transport.
