Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 molH2/gcath. [Display omitted] •Superprotonic CsH2PO4 enables electrochemical cell operation at 250°C•Ammonia decomposition catalyst integrated with hydrogen electrooxidation catalyst•Ammonia converted to hydrogen with 100% faradic efficiency•Hydrogen production rate of 1.5 mol per gram catalyst per hour at 0.4 V bias Ammonia has received increasing attention in recent years as a possible energy carrier, in particular, as a carrier of hydrogen for use in fuel cells. The traditional approach of thermal decomposition suffers from high concentrations of residual ammonia, which poison the catalysts in polymer electrolyte membrane fuel cells, whereas newer strategies based on electrochemical decomposition in aqueous solution operate at high overpotentials, implying low efficiency. Our approach integrates a thermal decomposition catalyst (Cs-promoted Ru on carbon nanotubes) with an all-solid-state electrochemical conversion cell (based on the proton-conducting electrolyte, CsH2PO4) in a device that is operable at 250°C. The resulting polarization curves indicate high current density at a modest voltage (far beyond what can be attained from alkali electrolyte cells), as well as catalyst utilization efficiency that far exceeds traditional thermal decomposition. Ammonia has received increasing attention in recent years as an enabler of a sustainable energy future, in particular, as a carrier of hydrogen for use in fuel cells. Using superprotonic CsH2PO4 and a bilayer cathode structure, we show ammonia-to-hydrogen conversion with 100% faradic efficiency. Cs-promoted Ru serves as the amm