Design and Characterization of Effective Ag, Pt and AgPt Nanoparticles to H2O2 Electrosensing from Scrapped Printed Electrodes

The use of disposable screen-printed electrodes (SPEs) has extraordinarily grown in the last years. In this paper, conductive inks from scrapped SPEs were removed by acid leaching, providing high value feedstocks suitable for the electrochemical deposition of Ag, Pt and Ag core-Pt shell-like bimetallic (AgPt) nanoparticles, onto screen-printed carbon electrodes (ML@SPCEs, M = Ag, Pt or AgPt, L = metal nanoparticles from leaching solutions). ML@SPCEs were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results were compared to those obtained when metal nanoparticles were synthesised using standard solutions of metal salts (MS@SPCEs). Both ML@SPCEs and MS@SPCEs exhibited similar cyclic voltammetric patterns referred to the electrochemical stripping of silver or the adsorption/desorption of hydrogen/anions in the case of platinum, proving leaching solutions extremely effective for the electrodeposition of metallic nanoparticles. The use of both ML@SPCEs and MS@SPCEs proved effective in enhancing the sensitivity for the detection of H2O2 in phosphate buffer solutions (pH = 7). The AgPtL@SPCE was used as proof of concept for the validation of an amperometric sensor for the determination of H2O2 within laundry boosters and antiseptic samples. The electrochemical sensor gave good agreement with the results obtained by a spectrophotometric method with H2O2 recoveries between 100.6% and 106.4%.

. Number of publications per year about screen-printed electrodes (total number of publications: 5800). Citation report obtained from the Web of Science when the keywords ("screen printed" and (electrode or strip)) were introduced as topic in the search. Accessed the 21 st of January of 2019. Figure S2. Scheme of the metal leaching process. (A) Scrapped screen-printed platinum electrodes (SPPtEs). (B) SPPtEs immersion into concentrated H2SO4. The image was taken when immersing the electrodes in the solution (for less than 1 min). It was observed that the dielectric (blue cover) of most of the electrodes started turning from blue to yellow. All of them turned to yellow after 30 min of immersion. (C) SPPtEs after H2SO4 treatment (30 min), rinsed thoroughly with ultrapure water to remove the dielectric; they were immersed in HNO3 for 10 min for the Ag-ink removal. (D) SPPtEs after HNO3 treatment (10 min). Note that the reference electrode and the electric contacts (made of silver ink) were removed in all the strips, while the platinum inkbased counter and working electrodes remained. (E) SPPtEs from the previous stage were immersed in boiling aqua regia for Pt leaching. F) Ceramic strips of SPPtEs after leaching. Figure S3. AgPtX@SPCEs obtained after the galvanic displacement step. (A) The silver pseudoreference electrode was protected with parafilm prior to the galvanic displacement process. It can be observed that the pseudo-reference electrode remains bright grey, as occurs with unmodified screen-printed carbon electrodes (SPCEs). (B) The pseudo-reference electrode was unprotected prior to the galvanic displacement process, thus Pt was additionally deposited onto the pseudoreference electrode.

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On the reverse scan of Figure S8B,C, a cathodic peak was observed at +0.3 V, which was 16 attributed to the electrochemical reduction of Ag2SO4 species according to the following reaction:

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The semicircle or arc region is related to the electron transfer rate of the ferrocyanide redox probe 35 at the electrode|solution interface, while the linear region close to 45º is related to the diffusional 36 limiting step of the electrochemical process. These EIS spectra were fitted to a standard Randel's 37 equivalent circuit (inset of Figure S9B), which consisted in an uncompensated resistance (R u ) due to 38 the electrolyte resistance, a charge transfer resistance ( R ct ) that depends on the dielectric and

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EIS measurements indicate that SPCEs modification with any of the herein studied nanoparticles 45 results in a decrease of the charge transfer resistance (Table S1), as can be seen from the reduction of 46 the semicircle arc at high frequencies in Figure S9. Therefore, as expected, the use of metallic 59 Table S1. Impedance data obtained by fitting the experimental data from Figure S9

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The values obtained for the different Ae are shown in Table S2.