Ab initio molecular dynamics simulations were employed to study the microstructure of water-methanol mixtures subject to external electric fields. The electric field has a complex effect on the hydrogen bond network in the mixtures. At low methanol concentrations the water molecules form a percolated network surrounding short chains of methanol molecules. At high concentrations the water and methanol molecules segregate forming two separate hydrogen bond networks. The application of the field affects the structural evolution of the hydrogen bond network and a surprising 'hollow channel' is formed in the methanol-rich mixtures when under moderate fields (similar to 0.50 V/angstrom). (C) 2015 Elsevier B.V. All rights reserved.