A system for producing hydrogen features a reactor including a reaction channel adapted to receive a reaction stream including a mixture of supercritical water and a hydrocarbon fuel. A catalyst is positioned in the reaction channel so that a product stream containing hydrogen is produced by a reaction in the reaction channel when the mixture is exposed to the catalyst; wherein the catalyst contains a catalytically active metal and a promoter in a metal format, selected from the group consisting of potassium, sodium, rubidium, lithium, cesium, beryllium, magnesium, calcium, strontium, and barium.