Redox processes at a nanostructured interface under strong electric fields

Abstract

Manipulation of chemistry and film growth via external electric fields is a longstanding goal in surface science. Numerous systems have been predicted to show such effects but experimental evidence is sparse. Here we demonstrate in a custom-designed UHV apparatus that the application of spatially extended, homogeneous, very high (>1 V nm(-1)) DC-fields not only changes the system energetics but triggers dynamic processes which become important much before static contributions appreciably modify the potential energy landscape. We take a well characterized ultrathin NiO film on a Ag(100) support as a proof-of-principle test case, and show how it gets reduced to supported Ni clusters under fields exceeding the threshold of +0.9 V nm(-1). Using an effective model, we trace the observed interfacial redox process down to a dissociative electron attachment resonant mechanism. The proposed approach can be easily implemented and generally applied to a wide range of interfacial systems, thus opening new opportunities for the manipulation of film growth and reaction processes at solid surfaces under strong external fields.

The quantum mechanics derived atomistic mechanism underlying the acceleration of catalytic CO oxidation on Pt(110) by surface acoustic waves

“…Such high electric fields are not expected under the SAW conditions, since many unobserved phenomena would be triggered at much lower field values. 30 Moreover such fields are unrealistic considering the thickness and screening of the Pt metallic layer, which would attenuate the electric field down to values ~1000 times smaller than required. 6 The effects of SAW-induced homogeneous strain on diffusion 31 can also be excluded as well as the major cause of the observed increase in COox efficiency, since the diffusion energy barriers are also sizable (the barrier to O-diffusion is 0.88 eV) and thus appreciably modified only by much larger values of the strain.…”

Atomistic and Electronic Structure Methods for Nanostructured Oxide Interfaces

“…Although we do not have space to go into details here, it can be mentioned that current-induced redox phenomena-i.e., electron capture and successive detachment of an oxygen atom-have been demonstrated in a custom-built surface science apparatus applied to a system in which a Ag(100) surface was covered by an NiO ultrathin film [124]. A strong homogeneous electric field of the order of 1 V/nm triggered dissociative attachment chemical processes reducing the NiO layer to Ni clusters in a resonant phenomenon, thus realizing a "surface-science electrochemical" analogue of STM-induced chemical reductions.…”

Computational Study of Adsorption of CO2, SO2, and H2CO on Free-Standing and Molybdenum-Supported CaO Films

“…31,27 Reduction of an Ag-supported NiO film was found to take place under the applied electric field of ∼1 V nm −1 . 33 Hydrogen adsorption energy on doped graphene was shown to increase up to 0.3 eV under the electric field of 1 V Å −1 . 29 Furthermore, the electric field has been shown to control the magnetism of nanostructures.…”

“…This is turn can directly influence adsorption due to the changes in the electronic structure of CaO films. Interestingly, manipulation of reactivity and morphology of a nanocatalyst structures by electric fields have been reported. − Experimental results demonstrate that morphology of the gold nanoclusters and dimers on a MgO surface and graphene can be controlled by applying electric field. , Reduction of an Ag-supported NiO film was found to take place under the applied electric field of ∼1 V nm –1 . Hydrogen adsorption energy on doped graphene was shown to increase up to 0.3 eV under the electric field of 1 V Å –1 .…”