Electroadhesion has many advantages over other adhesion methods such as pneumatic, hydraulic, magnet, etc. The applications include electrostatic chucks and grippers. Recently, electroadhesion has been adopted for robots working in limited environments. The electro-adhesive climbing robots can be used for inspection and exploration in a variety of conditions. The electroadhesion robots often have a limited adhesion force. In this paper, we propose a novel pad structure improving the adhesion force. An additional insulating layer prevents the discharge from the high voltage application and increases the adhesion force per unit area. The electroadhesion forces were compared for the different pad materials and electrode structures and were partly confirmed as the theoretical model. The proposed pad was used for a climbing robot wheel. The climbing robot weighs approximately 3 kg and can manage to 3 kg of extra weight on metal walls. Experiments showed a 90-degree gradability for the climbing robot.