NOVELTY - Operating a hybrid sulfur electrolyzer (10) to generate hydrogen involves providing an anolyte (20) with a concentration of sulfur dioxide, to an electrolyzer cell (12); and applying current to the cell. During steady state generation of hydrogen a plot of applied current density versus concentration of sulfur dioxide is below a boundary line. The boundary line is linear and extends through an origin of graph and has a slope of 0.001 in which the current density measured in mA/cm2 and the concentration of sulfur dioxide measured in moles of sulfur dioxide per liter of anolyte.    USE - For operating a hybrid sulfur electrolyzer to generate hydrogen (claimed).    ADVANTAGE - The method operates a hybrid sulfur electrolyzer so that unwanted sulfur formation is either reduced or eliminated. The reduction or elimination of a sulfur layer allows the hybrid sulfur electrolyzer to operate to generate hydrogen without a significant increase in the voltage needed to drive the electrolyzer cell for such production.    DETAILED DESCRIPTION - Operating a hybrid sulfur electrolyzer (10) to generate hydrogen involves providing an anolyte (20) having a concentration of sulfur dioxide, to an electrolyzer cell (12); and applying current to the electrolyzer cell such that a current density is established. During steady state production of hydrogen generation a plot of the applied current density on an X-axis of a graph versus the concentration of sulfur dioxide on a Y-axis of the graph is below a boundary line on the graph. The boundary line is linear and extends through an origin of the graph and has a slope of 0.001 in which the X-axis of the graph is current density measured in mA/cm2 and the Y-axis of the graph is concentration of sulfur dioxide measured in moles of sulfur dioxide per liter of anolyte. The anolyte has water; and sulfuric acid (30 wt.%). The electrolyzer cell has a proton exchange membrane that is made of NAFION 115 (RTM: composite membrane). The steps of providing an anolyte and applying current occur during the steady state production of the hybrid sulfur electrolyzer, and further involves a start up sequence by loading anolyte that does not have any concentration of sulfur dioxide into an anolyte tank; impressing a voltage to the electrolyzer cell that is less than that needed to accomplish water electrolysis of hydrogen; heating the electrolyzer cell and the anolyte; slowly adding sulfur dioxide to the anolyte such that anolyte pressure is increased and concentration of sulfur dioxide in the anolyte is increased; obtaining the amount of concentration of the sulfur dioxide in the anolyte by use of the temperature and pressure of the anolyte, where the plot of the applied current density on the X-axis of the graph versus the concentration of sulfur dioxide on the Y-axis of the graph is below the boundary line; changing a power supply to the electrolyzer cell to current control once a target current is reached; and decreasing the concentration of sulfur dioxide in the anolyte until the first indication of an increase in voltage in the electrolyzer cell, where the decreasing step is performed only if an increase in concentration of sulfur dioxide in the anolyte does not cause a decrease in voltage of the electrolyzer cell. The voltage to which the electrolyzer cell is impressed in the impressing step is 0.9 volt. An INDEPENDENT CLAIM is included for determining operating parameters for a hybrid sulfur cycle, involving obtaining data points of mass transfer limitation of a hybrid sulfur electrolyzer; plotting the obtained data points with respect to components of current density and sulfur dioxide concentration; plotting a boundary line in view of the plotted data points; and establishing operating parameters of the hybrid sulfur cycle that fall on one side of the boundary line.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a hybrid sulfur electrolyzer facility.    Hybrid sulfur electrolyzer test facility (10)    Electrolyzer cell (12)    Anode (14)    Cathode (16)    Anolyte (20)    Backpressure regulator (28)    Sulfur dioxide pump (30)    Water pump (32)    Anolyte tank (34)    Gear pump (36)    Motorized valve (42)    Waste drum (44)