The salt splitting performance of an electrolysis cell incorporating a novel composite membrane consisting of a thin film of an amorphous ceramic with NASICON composition (Na1+xZr2SixP3-xO12, 0 less than or equal tox less than or equal to3) deposited on commercial cation-selective polymeric membranes was evaluated. We have investigated how the ceramic film thickness and the technique of deposition affected the base current efficiency (BCE) for the production of sodium hydroxide from sodium sulfate. It was found that when full coverage of the polymeric substrate was achieved, the ceramic film improved the salt-splitting performance of the polymeric membrane, even when localized surface defects were present. The study showed that the BCE of the electrolysis cell was the same whether the cation-selective composite membrane used was formed by pulsed laser deposition or by sputtering. Operating the cell above room temperature, and at a high anolyte concentration increased the base current efficiency for sodium hydroxide production.