Investigation of the electrochemical oxidation reaction of the borohydride anion in palladium layers on Pt(111)

详细信息    查看全文

• 作者：Vanessa L. Oliveira^a ; ^b ; ^c ; ^{vanessa.luciane.oliveira@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; ^{vanessa.l.oliveir@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Eric Sibert^a ; ^b ; Yvonne Soldo-Olivier^a ; ^b ; ^d ; Edson A. Ticianelli^c ; Marian Chatenet^a ; ^b ; ^e
• 关键词：Borohydride oxidation reaction (BOR) ; Pt(111) single crystal ; Palladium pseudomorphic layers ; underpotential deposition (UPD) ; hydrogen insertion
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：10 August 2016
• 年：2016
• 卷：209
• 期：Complete
• 页码：360-368
• 全文大小：1572 K

文摘

The electrooxidation reaction of 0.001 mol L⁻¹ NaBH₄ in 0.1 mol L⁻¹ sodium hydroxide solution is studied on a set of Pd_xML/Pt(111) surfaces with x = 0 (Pt(111) substrate), 1, 2, 5, 10 and 16 monolayers (ML) as equivalent thickness. The Pd_xML/Pt(111) surfaces are all more active than Pt(111), and present smaller reaction onset potential and larger faradaic current in the kinetics region. The most active surface, at 400 rpm is Pd_1ML/Pt(111). As hydrogen insertion is not possible in this case, the superior activity of Pd_xML/Pt(111) surfaces cannot be linked to the formation of Pd-hydrides. Instead, the activity improvement of the Pd_xML/Pt(111) surfaces versus Pt(111) may originate from (i) the larger oxophilicity of Pd than Pt facilitates the removal of strongly-adsorbed BH_ad intermediates in a Langmuir-Hinshelwood pathway, (ii) the redirection of the heterogeneous hydrolysis of BH₄⁻ towards the partial dissociation into BH₃ species, that are oxidized faster than BH_ad species and (iii) the slower hydrogen evolution reaction (HER) at Pd than at Pt surface, which shifts negatively the BOR onset potential and oxidation current generation. Pd_xML/Pt(111) surfaces are sensitive to surface poisoning and deactivation by either the final products of the BOR (BO_x) and/or their intermediates (BH_x,ad species), but this deactivation is much less than observed for Pt(111). Finally, the Pd_xML/Pt(111) and Pt(111) surfaces lose their long-range order after being used for the BOR, most likely because of the “irreversible” adsorption of strong adsorbates (e.g. BO_x species), even if their restructuration cannot be completely ruled out.