Polymer electrolyte membrane fuel cells (PEMFCs) running on hydrogen are attractive alternative power supplies for a range of applications, with in situ release of the required hydrogen from a stable liquid offering one way of ensuring its safe storage and transportation before use. The use of methanol is particularly interesting in this regard, because it is inexpensive and can reform itself with water to release hydrogen with a high gravimetric density of 18.8 per cent by weight. But traditional reforming of methanol steam operates at relatively high temperatures (200-350 degrees Celsius), so the focus for vehicle and portable PEMFC applications has been on aqueous-phase reforming of methanol (APRM). This method requires less energy, and the simpler and more compact device design allows direct integration into PEMFC stacks. There remains, however, the need for an efficient APRM catalyst. Here we report that platinum (Pt) atomically dispersed on α-molybdenum carbide (α-MoC) enables low-temperature (150-190 degrees Celsius), base-free hydrogen production through APRM, with an average turnover frequency reaching 18,046 moles of hydrogen per mole of platinum per hour. We attribute this exceptional hydrogen production-which far exceeds that of previously reported low-temperature APRM catalysts-to the outstanding ability of α-MoC to induce water dissociation, and to the fact that platinum and α-MoC act in synergy to activate methanol and then to reform it.
The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.
Methane activation at moderate conditions and with good selectivity for value-added chemicals still remains a huge challenge. Here, we present a highly selective catalyst for the transformation of methane to methanol composed of highly dispersed iron species on TiO2. The catalyst operates under moderate light irradiation (close to one sun) and at ambient conditions. The optimised sample shows a 15% conversion rate for CH4 with an alcohol selectivity of over 97% (methanol selectivity over 90%) and a yield of 18 moles of alcohol per mole of iron active site in just three hours. XPS measurements with and without Xenon lamp irradiation, light intensity-modulated spectroscopies, photoelectrochemical measurements, XANES and EXAFS spectra, as well as isotopic analysis confirm the function of the major ironcontaining species, namely FeOOH and Fe2O3, which enhance charge transfer and separation, decrease the overpotential of the reduction reaction and improves selectivity towards methanol over CO2 production.
In situtransformation of Pd into β-PdH is the origin of the high selectivity for CO in the electrochemical CO2reduction reaction using Pd as the electrocatalyst.
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