H2 production through electro-oxidation of SO2: identifying the fundamental limitations
Date
2014Author
Kriek, Roelof J.
Rossmeisl, Jan
Siahrostami, Samira
Björketun, Márten E.
Metadata
Show full item recordAbstract
Sulphur dioxide (SO2), a known industrial pollutant and pulmonary irritant, is emitted to the atmosphere
in excess of 120 Mt per annum. Great strides have been taken to reduce SO2 emissions, but with the
growth of specifically China, and to a lesser extent India, it is on the rise again. The electrolysis of
aqueous solutions of dissolved SO2 holds huge environmental potential in that SO2 is converted to
sulphuric acid (H2SO4) and at the same time hydrogen gas is produced. A further benefit or incentive is
that a sulphur depolarised electrolyser (SDE) operates at an applied potential that is about one volt lower
than that of a regular water electrolyser. In taking this technology forward the greatest improvement to
be made is in developing a suitable electrocatalyst, which is also the ‘lowest hanging fruit’ in that very
limited research and development has been conducted on the electrocatalyst for this process. In this
work, density functional theory is employed to model the electro-oxidation of SO2 on single crystal
planes of the 4d and 5d transition metals. Two reaction mechanisms are considered, a HSO3
intermediate pathway and a SO3 intermediate pathway. The binding energies of all intermediates are
found to scale with the surface reactivity (measured as the adsorption of OH). Irrespective of the
pathway water needs to be activated and reduction of SO2 to elemental sulphur must be avoided. This
requirement alone calls for an electrode potential of at least 0.7–0.8 V for all the investigated transition
metals and thus challenges the proclaimed goal to operate the SDE at 0.6 V. A high chemical barrier is
further found to severely limit the oxidation reaction on reactive metals. A much higher catalytic activity
can be obtained on precious metals but at the cost of running the reaction at high overpotentials
URI
http://hdl.handle.net/10394/16572http://dx.doi.org/10.1039/c4cp00705k
http://pubs.rsc.org/en/content/articlepdf/2014/cp/c4cp00705k