to produce S and steam (often referred to as the "catalytic" step). In the reaction scheme proposed here, SO 2 is by the chemical reduction of H 2 SO 4 (as described in a later section of this manuscript) and so only the second (catalytic) step is needed. Figure shows thermodynamic data for reaction of H 2 S and CS 2 oxidized by SO 2 or H 2 O. Figure shows that in the temperature range from the melting point of sulfur to those typically used for the catalytic Claus reaction, (120-330 °C) the reactions listed are both exothermic and exergonic. The oxidation of CS 2 by SO 2 is the most exergonic reaction below 330 °C, and CS 2 has been shown experimentally to be preferentially oxidized before H 2 S in this system. The catalytic Claus reaction between H 2 S and SO 2 is typically completed in stages with a final temperature around 120 °C to reduce the propensity for the reverse reaction and maintain the generated S as a low-viscosity liquid. While typical Claus plants carry this reaction out multiple times to achieve high (>99%) conversion efficiency, in the scheme described here, we propose that only 2/3 of the H 2 S must be converted back to S to continue the sulfur-reforming of biomass step of the proposed cycle. Residual unreacted H 2 S can be utilized in the next step for the chemical reduction of H 2 SO 4. The required stoichiometry of this cycle suggests that a single pass through a catalyst bed is likely to be sufficient and that the scheme we describe is highly tolerant to differences in conversion efficiency. It has been noted previously that in the 2-step Claus process, the oxidization of H 2 S into S and H 2 O effectively wastes the protons that could be used for H 2 production because it requires less energy to abstract H 2 from H 2 S compared to H 2 O. This has motivated the development of numerous methods to decompose H 2 S to liberate the H 2 , including direct thermal decomposition, electrolysis, indirect decomposition with iodine, and others. However, to date, none of these alternative methods have achieved large-scale industrial implementation due to significant technical challenges. The cycle we propose here avoids many of these pitfalls by using H 2 S as a chemical reducing agent to regenerate a SO 2 electrochemical cell. The heat generated by the catalytic Claus step may also be utilized to drive the subsequent steps of the cycle. Step 3: Chemical reduction of H 2 SO 4 :