Details

Autor(en) / Beteiligte

• Attard, Gary A.
• Souza-Garcia, Janaina
• Martínez-Hincapié, Ricardo
• Feliu, Juan M.

Titel

Nitrate anion reduction in aqueous perchloric acid as an electrochemical probe of Pt{1 1 0}-(1 × 1) terrace sites

Ist Teil von

• Journal of catalysis, 2019-10, Vol.378, p.238-247

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2019

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• [Display omitted] •Pt{1 1 0}-(1 × 1) site identified as most active for nitrate reduction.•Linear correlation between nitrate reduction current density and number of Pt{1 1 0}-(1 × 1) active sites.•Correlation may be used to estimate number of Pt{1 1 0}-(1 × 1) sites present at polycrystalline and nanoparticle Pt surfaces.•Pt{1 1 0} structure highly sensitive to ambient cooling conditions.•CO cooling favours formation of Pt{1 1 0}-(1 × 1).•Argon, nitrogen, hydrogen and oxygen cooling favour mixed (1 × 1)/(1 × 2) disordered phases. The electrochemical reduction of nitrate anions in aqueous 0.1 M perchloric acid has been studied using Pt(S)-[n{1 1 0} × {1 1 1}] and Pt(S)-[n{1 1 0} × {1 0 0}] single crystal electrodes. It is demonstrated that the presence of Pt{1 1 0} adsorption sites is associated with a single, broad nitrate reduction peak centred at 0.18 V (RHE). Moreover, depending on the cooling environment used after flame-annealing (CO, H2, Ar, air, nitrogen), the surface concentration of such sites varies which in turn regulates the nitrate reduction current density achievable for a given stepped Pt{h k l} electrode. The origin of this phenomenon is the propensity of the clean Pt{1 1 0} basal plane (and vicinal surfaces containing this plane) to reconstruct towards a stable (1 × 2) phase with strong CO chemisorption favouring formation of larger Pt{1 1 0}-(1 × 1) domains. In contrast, argon/air-cooling appears to promote the development of a largely (1 × 2) reconstructed surface which is much less active for nitrate reduction since the surface density of Pt{1 1 0}-(1 × 1) terrace sites is significantly diminished. Interestingly, hydrogen-cooling affords nitrate reduction activity intermediate between these two extremes. We suggest that under this particular preparation condition, a partially deconstructed (1 × 1) phase forms containing the “excess” 50% of surface atoms (originating from the (1 × 2) phase) sitting proud of the surface in the form of small (1 × 1) islands, together with residual (1 × 2) missing row regions. Hence, after hydrogen cooling, the nominal Pt{1 1 0} surface plane is speculated to exhibit a wider distribution of smaller terrace widths than found with CO cooling together with residual areas of (1 × 2). The weaker chemisorption of hydrogen apparently limits the size of the Pt{1 1 0}-(1 × 1) domains achievable and consequently, nitrate reduction activity is diminished. Based on these findings, it is proposed that nitrate reduction may be used as a quantitative electrochemical probe of Pt{1 1 0}-(1 × 1) sites at Pt nanoparticles in an analogous fashion to the method of ammonia electrooxidation presently used to quantify the surface abundance of Pt{1 0 0} sites.