German team doubles activity of water electrolysis catalysts for H2 production with monolayer of copper on platinum
A team from the Ruhr-Universität Bochum, Technische Universität München and Universiteit Leiden has doubled the catalytic activity of electrodes for water electrolysis by applying a monolayer of copper the platinum electrodes. The resulting electrodes are the most active electrocatalysts ever reported for the HER (hydrogen evolution reaction) in acidic media under comparable conditions, to the best of their knowledge, wrote the authors in an open-access paper in the journal Nature Communications.
Only about 4% of global hydrogen production is via water electrolysis, according to a 2012 analysis (Bičáková and Straka). The main impediments to a wider commercialization are the high energy losses in electrolyzers due to the insufficient activity of state-of-the-art electrodes.
Modern polymer electrolyte membrane (PEM) electrolyzers thus require larger platinum loadings (~0.5–1.0 mg cm-2) than those in PEM fuel cell anodes and cathodes combined (~0.5 mg cm-2).
Thus, the German team suggested, catalyst optimization would help in substantially reducing the costs for hydrogen production using this technology.
Here we show that incorporating (sub)monolayer amounts of copper (Cu) to platinum (Pt) enhances the catalytic activity ~2 times at low overpotentials, surpassing the highest HER-specific activities reported under similar conditions. These results are rationalized in terms of a structure-sensitive analysis of hydrogen adsorption on Pt- and Cu-modified Pt surfaces that also explains why polycrystalline Pt is more active than Pt(111) towards the HER.—Tymoczko et al.
The team headed by Prof. Dr. Aliaksandr Bandarenka from the Department of Physics of Energy Conversion and Storage in Munich and Prof. Dr. Wolfgang Schuhmann from the Center for Electrochemical Sciences in Bochum has calculated how strongly intermediates must adhere to the electrodes to most efficiently facilitate the reaction. The analysis revealed that traditional electrodes from platinum, rhodium and palladium bind the intermediates a bit too strongly.The researchers modified the properties of the platinum catalyst surface by applying a layer of copper atoms. With this additional layer, reaction intermediates could desorb a bit more easily from the catalyst surface. Positioning copper atoms into the subsurface layer of platinum weakens the surface binding of adsorbed H-intermediates, providing the two-fold activity increase.
The group observed another useful side effect: the copper layer extended the service life of the electrodes, for example by rendering them more corrosion-resistant.
In addition, the research on this reaction allows us to test, how well we can design catalyst surfaces by precisely positioning different metal atoms—knowledge many other catalytic processes might benefit from.—Aliaksandr Bandarenka
J. Tymoczko, F. Calle-Vallejo, W. Schuhmann, A. S. Bandarenka (2016) “Making the hydrogen evolution reaction in polymer electrolyte membrane electrolyzers even faster,” Nature Communications doi: 10.1038/NCOMMS10990
Bičáková, O. & Straka, P. (2012) “Production of hydrogen from renewable resources and its effectiveness,” Int. J. Hydrogen Energy 37, 11563–11578 doi: 10.1016/j.ijhydene.2012.05.047