April 2, 2014
Pure strain effects in catalysis
Strain shows a systematic shift.
Strain has been known to effect catalytic reactions by changing the width, and thus the relative position, of the d-band of the surface atoms. However, to induce strain in a system, it has generally been necessary to achieve this by methods that also chemically modify the surface reactivity. An example is through the use of pseudomorphic overlayers, which deposit one element (e.g. Pd) on top of a crystal of another (e.g., Ir), such that it takes the lattice constant of the substrate. However, the pseudomorphic layer also feels the chemical properties of the substrate. This is known as the ``ligand'' effect, which is typically coupled to the strain effect.
New experimental techniques coming out of the solid mechanics and materials science community are showing ways to mechanically induce strain in a catalyst without the use of concurrent ligand effect. Thus, a pure strain effect can be expected and observed. In research recently reported in The Journal of Physical Chemistry C, Tuhina Adit Maark has shown that the strain and ligand effects can be cleanly separated computationally, as illustrated in the figure to the right for Pd overlayers above various substrates. The strain effect produces a systematic shift in the binding strength of a probe adsorbate, H, while the ligand effect exhibits a much more scattered effect on the binding strength. Importantly, this research identifies a compressive region of Pd in which Pt-like activity for the hydrogen evolution reaction could conceivably be achieved, without resorting to expensive alloys with precious metals. This suggests ways to produce catalysts for water splitting at a significantly reduced cost.
Read the article in the Journal of Physical Chemistry C.
