The GH fixture also plays a pivotal role in the preparation of the WE electrolyte, which commences by closing the gas inlet port and applying a ca. 100 Torr vacuum on the center port of the GDL interface piston, which also evacuates the WE fixture through the porous GDE. By closing the electrolyte pumping port of the WE fixture and connecting the electrolyte manifold pump to an electrolyte reservoir open to atmosphere, the vacuum within the WE fixture pulls electrolyte into the fixture and against the GDE. While any trapped gas between the electrolyte and GDE is readily evacuated, the electrolyte does not flow through the GDE due to the hydrophobicity of the GDL. This initial wetting of the GDE automates one of the trickiest parts of traditional GDE cell preparation. We note that the tubing for the electrolyte manifold port approaches but not touches the membrane. The proximity helps ensure that no bubbles get caught on the membrane surface, which could cause an open circuit condition, and the small displacement and angled cut of the tube ending helps ensure that the membrane does not seal the tube end upon commencement of the vacuum-fill procedure.