Hydrogen production from formic acid decomposition at room temperature using a Ag–Pd core–shell nanocatalyst Karaked Tedsree 1 , Tong Li 2 , Simon Jones 1 , Chun Wong Aaron Chan 1 , Kai Man Kerry Yu 1 , Paul A. J. Bagot 2 , Emmanuelle A. Marquis 2 , George D. W. Smith 2 and Shik Chi Edman Tsang 1 * Formic acid (HCOOH) has great potential as an in situ source of hydrogen for fuel cells, because it offers high energy density, is non-toxic and can be safely handled in aqueous solution. So far, there has been a lack of solid catalysts that are sufficiently active and/or selective for hydrogen production from formic acid at room temperature. Here, we report that Ag nanoparticles coated with a thin layer of Pd atoms can significantly enhance the production of H 2 from formic acid at ambient temperature. Atom probe tomography confirmed that the nanoparticles have a core–shell configuration, with the shell containing between 1 and 10 layers of Pd atoms. The Pd shell contains terrace sites and is electronically promoted by the Ag core, leading to significantly enhanced catalytic properties. Our nanocatalysts could be used in the development of micro polymer electrolyte membrane fuel cells for portable devices and could also be applied in the promotion of other catalytic reactions under mild conditions. H ydrogen has attracted an increasing level of attention as an important energy vector when combined with polymer elec- trolyte membrane (PEM) fuel cell technology, and may play a very significant role in power generation in the future. In portable electronic appliances such as cell phones, MP3 players, laptop com- puters and similar niche products (0.5–100 W), the use of micro fuel cells is deemed to be more energy-efficient than battery technol- ogy 1 . Low-temperature PEM fuel cells and micro fabrication tech- nologies are therefore potentially the preferred choices for these consumer products. There are a number of ways of obtaining hydro- gen from renewable and non-renewable sources on a large industrial scale, but the storage and transfer of hydrogen in solid systems for mobile use is difficult because of poor volumetric and weight energy densities 2 . In addition, ultrapure hydrogen gas is required by PEM fuel cells. Specifically, the gas stream has to be free from CO gas (,10 ppm), or the catalytic performance of the fuel cells will be degraded significantly 3 . On-board reforming of organic com- pounds with downstream multistage CO post-treatments such as the water gas shift (WGS) reaction, selective oxidation of CO to CO 2 (SELOX), hydrogenation of CO to methane or membrane technol- ogy is not applicable. This is because these cumbersome multistage processes commonly take place at elevated temperatures, precluding their use in small portable devices where space and heat manage- ment are critical. In situ hydrogen production from formic acid decomposition Hydrogen stored in a chemical form as a liquid organic compound for on-demand in situ release, at room temperature and without CO contamination, seems to be a promising direction for mobile fuel cells. The primary liquid fuel can be stored in a disposable or recycl- able cartridge that is replaceable and readily available. Organic com- pounds such as formic acid, which is nontoxic and a liquid at room temperature (density, 1.22 g cm 23 ), have been widely used as hydrogen sources in liquid-phase transfer hydrogenation reactions under ambient conditions 4 . The decomposition of formic acid can follow two possible pathways, which are dependent on the catalytic surface, formic acid concentration and temperature: HCOOH  CO 2 + H 2 : DG =−48.4 kJ mol −1 (1) HCOOH  CO + H 2 O : DG =−28.5 kJ mol −1 (2) Reaction (1) is the reversible reaction of CO 2 hydrogenation (CO 2 þ H 2  HCOOH), and is considered to be a promising hydrogen- generation process. Recently, there have been reports of the decomposition of formic acid in excess amine over homogeneous Ru catalysts at ambient temperature. Excellent catalytic activities of some optimized catalytic species for this reaction have been reported 5 . Some improvements to reduce volatility have also been made 6,7 . Nevertheless, the separation issues and the use of organic solvents, ligands and additive(s) lead to severe difficulties in device fabrication. There have been very few studies using solid cat- alysts, and these were all tested using vapour or liquid media at elev- ated temperatures 8–11 . For example, there have been two independent reports 10,11 of active core–shell PdAu/C catalysts for hydrogen production from formic acid dehydrogenation at elevated temperatures (.50 8C), but these catalysts also generated CO gas and/or were inactive at low temperature. One of these studies reported 30 ppm CO and a high content of formic acid and water in the resultant hydrogen-gas stream at 90 8C (ref. 11). Despite the fact that some solid catalysts demonstrated a good degree of activity, rapid catalyst deactivation and concomitant CO production (from reaction (2)) at the level of tens to hundreds of ppm were generally reported 8,10 . These studies should prompt further careful analysis and assessment of the effects of CO on fuel cell catalysts 8–10 . More importantly, processing difficulties at elevated temperatures (.50 8C) owing to the volatility of the formic acid/water and the 1 Wolfson Catalysis Centre, Department of Chemistry, University of Oxford, Oxford, OX1 3QR, UK, 2 Department of Materials, University of Oxford, Oxford OX1 3PH, UK. *e-mail: edman.tsang@chem.ox.ac.uk ARTICLES PUBLISHED ONLINE: 10 APRIL 2011 | DOI: 10.1038/NNANO.2011.42 NATURE NANOTECHNOLOGY | VOL 6 | MAY 2011 | www.nature.com/naturenanotechnology 302