Voltammetric response of hydrogen adsorbates on platinum in acid solutions: a possible H-adatom subsurface state

Abstract

Fo ram apli ca das ro ti nas com bi na das de po ten ci al, en vol ven do var re du ras vol ta mé t ri cas e pa radas de po ten ci al, na re gião dos ad-átomos de hi dro gê nio so bre ele tro dos de Pt, em di fe r en tes so luções áci das, para pro du zir um au men to da cor ren te de pico da ele tro-desorção do "ter ce i r o" áto mo de hi dro gê nio que apa re ce cer ca de 0.22 V vs. RHE. Este pico pode ser ob ser va do para ele tro dos de Pt de di fe ren tes to po gra fi as. Apa ren te men te, a con tri bu i ção ca tó di ca cor res pon den te apa re ce numa re gião de po ten ci a is li ge i ra men te mais po si ti vos que o po ten ci al li mi ar da re a ç ão de des pren di mento de hi dro gê nio. A di fe ren ça en tre os po ten ci a is de pico re fe ren tes as re a ções re dox con ju ga das é con sis ten te com uma apre ciá vel ir re ver si bi li da de do pro ces so. A pe que na car ga en v ol vi da nes te par de pi cos é es pe ra da para es ta dos sub-superficiais e in ters ti ci a is dos ad-átomos de hi dr o gê nio so bre Pt. Esse tipo de es tru tu ra tem sido pre di ta por cál cu los da quí mi ca quân ti ca.Com bi ned po ten ti al rou ti nes in vol ving vol tam me tric swe eps and po ten ti al hol dings c o ve ring the H-adatom po ten ti al ran ge were ap pli ed to Pt elec tro des in dif fe rent aque ous acid so lu ti ons to pro du ce an enhan ce ment of the "third" H-atom elec tro de sorp ti on cur rent peak at ca. 0.22 V vs. RHE . This peak can be ob ser ved for Pt elec tro des of dif fe rent to po grap hi es. Se e mingly, the cor respon ding cat ho dic cur rent con tri bu ti on ap pe ars in a po ten ti al ran ge slightly more po s i ti ve than the hydro gen evo lu ti on re ac ti on thres hold po ten ti al. The peak po ten ti al dif fe ren ce re la ted to the con juga ted re dox re ac ti ons is con sis tent with an ap pre ci a ble ir re ver si bi lity of the pro cess. The small charge in vol ved in this pair of pe aks is ex pec ted from a sub sur fa ce and an in ters ti ti al H-a datom sta te on Pt. This type of struc tu re has been pre dic ted from quan tum che mistry cal cu la ti ons. Key words: pla ti num elec tro des, hydro gen evo lu ti on, H-adatoms, third H-adatom cur rent peak Intro duc ti onThe hydro gen evo lu ti on re ac ti on ( HER), one of the most im por tant pro ces ses in elec tro ca taly sis, has been used as a pro toty pe for se ve ral elec tro de re ac ti ons [1][2][3][4][5][6][7] . De pen ding on the na tu re of the me tal/so lu ti on in ter fa ce, the ki ne tics of the HER has been ex pla i ned through dif fe rent re ac ti on path ways in volving the par ti ci pa ti on of H-adatoms as re ac ti on in ter me di a tes. Accor dingly, de pen ding on the type of ad sorp ti on isot herm which H-adatoms obey, ki ne tic equa ti ons de ri ved from dif ferent re ac ti on path ways ac count for spe ci fic po ten ti al and time de pen den ci es of θ, the de gree of elec tro de sur fa ce co ve ra ge by re ac ti on in ter me di a tes 1-3 .Ho we ver, in con ven ti o nal me cha nis tic ap pro a ches t...

Influence of H- and OH-adsorbates on the ethanol oxidation reaction – a DEMS study

“…More specifically, the ECSA from Pt-SnO 2 /C and Pt-Rh-SnO 2 /C may be underestimated (and thus d Elec overestimated) due to CO ad electrooxidation probably occurring during the chronoamperometry at E ad = 0.15 V vs. RHE preceding the CV. 53,54 On the one hand, the oxide region on Rh-and Sn-based electrocatalysts, i.e. on Rh/C, Pt-Rh/C, Pt-SnO 2 /C and Pt-Rh-SnO 2 /C, starts at much lower potentials than on Pt/C (E = 0.8 V vs. RHE).…”

“…4 presents cyclic voltammograms of the supporting electrolyte (0.5 M H 2 SO 4 ) on Pt/C, Rh/C, Pt-Rh/C, Pt-SnO 2 /C and Pt-Rh-SnO 2 /C. The usual features of the so-called hydrogen and oxygen regions of Pt-based electrodes can be observed 53,54. On the one hand, the oxide region on Rh-and Sn-based electrocatalysts, i.e.…”

Hydrogen adsorption on nano-structured platinum electrodes

“…Several papers have studied the nature of this peak. [8][9][10][11][12][13][14][15] The peak appears aer the platinum electrode has been oxidized at sufficiently high potential or when the platinum electrode has been contact with a sufficiently high hydrogen (H 2 ) concentration, and the oxidation of the species involved in the peak is slow and irreversible compared to the other peaks in the hydrogen region. There appears to be a lack of consensus in the literature as to whether the peak involves the formation of some kind of subsurface hydrogen, or whether it is purely surface conned.…”

Hydrogen-Induced Step-Edge Roughening of Platinum Electrode Surfaces

“…20,23,24 This peak in current appears near 0.22 V RHE , between peaks corresponding to the exchange of adsorbed hydrogen with hydroxide and water on (110) and on (100) step sites (hence the name “third-peak”), in cyclic voltammograms measured on polycrystalline or single-crystalline platinum electrodes after these electrodes are held at high potential (above ∼1.3 V RHE ) 23−28 or low potential (below 0.17 V RHE ). 23−25,29 It has been suggested to be due to the formation of a unique surface or subsurface binding site by oxygen (hydrogen) adsorption at high (low) potentials that is then filled by hydrogen at low potentials, 24,26,28 or formed at low potentials by the absorption/desorption of subsurface atomic hydrogen 30,31 or subsurface molecular hydrogen. 27 Work performed with single-crystal electrodes has shown that the third peak is exclusively related to the presence of (110) step sites, (110) terraces, or (110)-(2 × 1) domains.…”