The electro-thermo-convection of a perfectly insulating liquid lying between a square enclosure and a heated inner circular cylinder is numerically investigated using a unified lattice Boltzmann method (LBM). The flow motion is driven by the thermal buoyant force and the Coulomb force due to a direct current (DC) electric field exerting on free space charges injected from the inner cylinder. Four lattice Boltzmann equations are used to solve all governing equations including the Navier-Stokes equations, the energy conservation equation and a simplified set of Maxwell's equations. It is found that the augmentation of heat transfer due to the electrical effect becomes significant when the electric driving parameter T above a critical threshold. For sufficiently high values of T, the flow is fully dominated by the Coulomb force, and the average Nusselt number becomes independent of Ra. The influence of the fluid properties and geometric parameter on heat transfer enhancement is also studied. (C) 2017 Elsevier Ltd. All rights reserved.