A closed‐loop proposal for hydrogen generation using steel waste and a prototype solar concentrator

An economically viable and environmental‐friendly method of generating PEM grade hydrogen has been proposed and is by the reaction of certain metals with steam, appropriately called ‘metal–steam reforming’—MSR. The drawbacks of conventional processes (hydrogen and carbothermic reduction schemes) are overcome by resorting to solution‐based reduction schemes and are made economically feasible using iron oxides from steel industry's mill‐scale waste. A novel aqueous‐based room temperature technique using sodium borohydride (NaBH₄) as the reducing agent has been developed that produces highly active nanoscale iron particles (～40 nm). By using hydrazine as an inexpensive and, compared with NaBH₄, more stable reductant, body centered cubic iron particles with ～5 nm edges were obtained via solvothermal process under mild conditions from acid digested mill‐scale waste. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation than the coarser microscale iron. The rate constants for the MSR were obtained for all the reduction schemes employed in this work and are given by k_hydrogen=0.0158 min^?1 k_carbon=0.0248 min^?1 k_{sodiumborohydride}=0.0521 min^?1 and k_hydrazine=0.1454 min^?1, assuming first order kinetics. Another innovative effort converted the magnetite waste directly into nZVI under solvothermal conditions, thus obviating the sluggish and time‐consuming acid dissolution step. This particular aspect has significant ramification in terms of time and cost of making the iron precursor. To initiate and sustain the somewhat endothermic MSR process, a solar concentrator consisting of a convex polyacrylic bowl with reflective aluminum coating was fabricated and evaluated. This unique combination of mill‐scale waste as iron source, hydrazine as reductant, mild process conditions and solar energy as the MSR actuator obviates several drawbacks plaguing the grand scheme of producing and delivering pure and humidified H₂ to a PEMFC stack. Copyright © 2008 John Wiley & Sons, Ltd.