Each witness who appears before the public utilities commission by its order shall receive the fees and mileage provided for under section 119.094 of the Revised Code, which shall be audited and paid by the state as other expenses are audited and paid, upon the presentation of proper vouchers sworn to by such witnesses and approved by the chairperson of the commission. No witness subpoenaed at the instance of parties other than the commission is entitled to compensation from the state for attendance or travel, unless the commission certifies that the witness’s testimony was material to the matter investigated.