A team led by Ecole Polytechnique Fédérale de Lausanne (EPFL) Professor Xile Hu has discovered that a molybdenum-based catalyst allows the electrolytic production of hydrogen at room temperature, and is inexpensive and efficient. The results provide new opportunities for the development of renewable and economic hydrogen production technologies. A paper on the work appears in the RSC journal Chemical Science.
Water splitting for hydrogen production consists of two half cell reactions; the hydrogen evolution reaction requires catalysts. While nickel-based catalysts are often employed in commercial alkaline electrolyzers, platinum and its composites are the most active catalysts for hydrogen evolution in an acidic medium, Hu et al. note. The large scale application of Pt catalysts is limited by their high cost and low abundance.
Extensive efforts have been devoted to the search of alternative catalysts containing only non-precious elements under heterogeneous conditions. Yet functional and robust catalysts operating with reasonable current densities (J) at low overpotentials (η) in water are scarce.
Recently, MoS2 nanoparticles have been identified as promising hydrogen evolution catalysts. Bulk MoS2 is a poor catalyst; nano-crystals of MoS2 and related metal sulfides, however, are more active...Notwithstanding the impressive advances, the practical implementation of these systems is hindered by their sophisticated and/or energy intensive preparation procedures, such as ultra-high vacuum conditions, reduction by H2S streams and annealing at elevated temperatures.
Here we report that amorphous molybdenum sulfide films are active hydrogen evolution catalysts. The catalysts are prepared at room temperature and atmospheric pressure, and in a simple, rapid, and scalable manner. Furthermore, compared to MoS2 nanoparticles, the amorphous molybdenum sulfide films exhibit higher activity.—Hu et al.
In their study, Hu et al. explored four different molybdenum sulfide films. The new catalysts exhibit many advantageous technical characteristics. They are stable and compatible with acidic, neutral or basic conditions in water. The study found that these amorphous molybdenum sulfide films are among the most active non-precious hydrogen evolution catalysts.
In their study, they found that significant geometric current densities are achieved at low overpotentials (e.g., 15 mA cm-2 at η = 200 mV) using these catalysts. The catalysis is compatible with a wide range of pHs (e.g., 0 to 13). The current efficiency for hydrogen production is quantitative. A 40 mV Tafel slope is observed, suggesting a rate-determining ion+atom step.
It was only by chance that the team made this discovery during an electrochemical experiment.
It’s a perfect illustration of the famous serendipity principle in fundamental research. Thanks to this unexpected result, we’ve revealed a unique phenomenon, but we don’t yet know exactly why the catalysts are so efficient.—Xile Hu
Further characterization and application of the catalyst, such as further stability studies and impedance analysis are currently underway.
Daniel Merki, Stéphane Fierro, Heron Vrubel and Xile Hu (2011) Amorphous Molybdenum Sulfide Films as Catalysts for Electrochemical Hydrogen Production in Water. Chemical Science doi: 10.1039/C1SC00117E