ELECTRIC FIELD EFFECT IN WATER DISSOCIATION ACROSS ATOMICALLY THICK GRAPHENE

  • Junhao Cai

Student thesis: Phd

Abstract

Intense electric fields can promote the dissociation reaction of weak electrolytes. Conventionally, high-voltage electrolysis cells are used to provide the required field intensity (~10^7 V/m) for molecules like ammonia and acetic acid. However, such a phenomenon in water demands a more intensive field of >10^8 V/m. Designing transport experiments with such high electric fields is difficult which makes observing a field effect in water much harder. Here in this thesis, we demonstrate that with a monolayer-graphene electrode that is selectively permeable to protons, it is possible to measure water dissociation reaction in a field of up to ~10^9 V/m. The water dissociation is accelerated by the strong electric field present in the electric double layer near the free-standing graphene electrode. The proton and hydroxide ions split from water molecules, they are then further separated across the two sides of the proton selective graphene interface. With a voltage bias of ~2 V, current densities of more than 10 A/cm^2 are achieved in the field-accelerated water electrolysis. This current density outperforms traditional electrolysers with an improvement of one-two orders of magnitude. Mass transport experiments show that the H2 and O2 gases are generated with 100% Faradaic efficiency, providing direct evidence for water electrolysis across the graphene electrode. These findings demonstrate a physical approach to accelerate chemical reactions, which could be extended to other reactions related to proton transport and beyond.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorIrina Grigorieva (Supervisor) & Marcelo Lozada Hidalgo (Supervisor)

Keywords

  • Water dissociation
  • Second Wien effect
  • Graphene

Cite this

'