# Selective Glycerol-to-glycerate Electro-oxidation on Cerium-modified Pt/C Nanocatalyst in an Alkaline Direct Alcohol Fuel Cell: Cogeneration of Energy and Value-added Products

Fabiano Cursi, Laurie Grimaud, Julie Rousseau, Karine Servat, Cláudia Morais, Teko Napporn, Adalgisa de Andrade, K. Boniface Kokoh

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## ► To cite this version:

Fabiano Cursi, Laurie Grimaud, Julie Rousseau, Karine Servat, Cláudia Morais, et al., Selective Glycerol-to-glycerate Electro-oxidation on Cerium-modified Pt/C Nanocatalyst in an Alkaline Direct Alcohol Fuel Cell: Cogeneration of Energy and Value-added Products. ChemElectroChem, 2024, 11 (3), 10.1002/celc.202300555. [DOI: 10.1002/celc.202300555](https://doi.org/10.1002/celc.202300555)

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# Selective Glycerol-to-glycerate Electro-oxidation on Cerium-modified Pt/C Nanocatalyst in an Alkaline Direct Alcohol Fuel Cell: Cogeneration of Energy and Value-added Products

Fabiano S. Cursi,[a, b] Laurie Grimaud,[b] Julie Rousseau,[b] Karine Servat,[b] Cláudia Morais,[b] Teko W. Napporn,[b] Adalgisa R. de Andrade,[*a, c] and K. Boniface Kokoh*[b]

Glycerol electro-oxidation reaction was performed in an alkaline environment with an anion exchange membrane fuel cell (AEMFC) operating in bath mode at low Pt-loadings. BAE-synthesized Pt/C and PtCe/C nanostructured catalysts were used as anode materials during 4-hour operation to selectively obtain 65% and 41% of glycerate as main product, respectively. The modification of Pt with Ce improved the catalytic activity of the Pt/C catalyst generating 30% more energy density after 4-hour operation by achieving a higher degree of glycerol oxidation in cogeneration with added-value products confirmed

by spectroelectrochemical (in situ FTIR) and liquid chromatography coupled with mass spectrometry (LC-MS) analyses. The bifunctional mechanism generated by the presence of Ce is used to explain the improvement in the catalytic activity of Pt/C, due to the properties of this rare earth element to adsorb oxygenated species (OH⁻) and promote oxidation. The cathode material was a polyol-synthesized PdFe/C electro-catalyst for ORR that presented impressive stability and tolerance to glycerol.

## Introduction

The world-wide overproduction of glycerol from tranesterification of vegetable oils into biodiesel has made this three-carbon polyol a molecule for long-time regarded as an industrial waste product.[1-7] It constitutes a large reserve of low-cost and renewable feedstock, and its oxidation can be of interest for two reasons: (i) its volumetric energy density (6.260 kWhL⁻¹) is an asset for energy conversion in a fuel cell, and (ii) its selective oxidation can pave the way for recovering value-added compounds such as glyceric, tartronic, and glycolic acids.[8] Glycerol is easy to store and is an environmentally-friendly

molecule that can be valorized through a series of processes, as reported by Ahmad et al.[5] One of these processes to add value to glycerol concerns its electrocatalytic conversion, where rather than handling with hazardous chemicals, the electron is used as a green reagent.[9] Glycerol electro-oxidation is a multi-electron transfer process,[10] and several of its oxidation products can be applied in the industry, as reported extensively.[11-13]

Glycerol oxidative conversion can be modulated to yield between 2 (glyceraldehyde) and 14 electrons (CO₂).[14] By designing the state of the material surface depending on the applied electrode potential, complete glycerol electro-oxidation can be achieved to increase the current density and hence the power density of the associated device (fuel cell). While a partial oxidation opens up the opportunity for cogeneration comprising simultaneous organic electrosynthesis (recovery of products at high commercial value) and energy conversion.

In the configuration of a Fuel Cell device, glycerol oxidation reaction (GOR) takes place in the anodic compartment, while oxygen reduction reaction (ORR) occurs at the cathode. Conversely to an acidic environment, where oxygenated species reactions are typically sluggish, an alkaline electrolyte greatly enhances glycerol oxidation kinetics.[1,15,16] In addition, other advantages of fuel cells for glycerol electro-oxidation over heterogeneous catalysis include the possibility of modulating product selectivity by controlling the current or electrode potential, not to mention that the cells operate at lower temperatures and without applied pressure.[17]

Due to its low d-band center (−2.25 eV), platinum (Pt) is pointed out as one of the most active materials for glycerol oxidation.[18,19] Because Pt is a precious metal (PGM), efforts have been devoted to reducing the amount of this metal in catalysts, either by lowering its loading charge or by the

<footnote>[a] F. S. Cursi, Prof. Dr. A. R. de Andrade
Department of Chemistry,
Faculty of Philosophy, Science and Letters at Ribeirão Preto,
University of São Paulo, 14040-901, Ribeirão Preto, SP, Brazil</footnote>

<footnote>[b] F. S. Cursi, L. Grimaud, J. Rousseau, Dr. K. Servat, Dr. C. Morais,
Dr. T. W. Napporn, Prof. Dr. K. B. Kokoh
Université de Poitiers, IC2MP UMR 7285 CNRS, Equipe SAMCat,
4 rue Michel Brunet, B27, TSA 51106, 86073 Poitiers Cedex 09, France
E-mail: boniface.kokoh@univ-poitiers.fr</footnote>

<footnote>[c] Prof. Dr. A. R. de Andrade
UNESP - National Institute of Alternative Technologies for Detection,
Toxicological Evaluation and Removal of Micropollutants and Radioactive
Substances (INCT-DATREM),
Rua Prof. Francisco Degni, 55, Araraquara, 14800-060, São Paulo State,
Brazil
E-mail: ardandra@usp.br</footnote>

<footnote>Supporting information for this article is available on the WWW under
https://doi.org/10.1002/celc.202300555</footnote>

<footnote>© 2024 The Authors. ChemElectroChem published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.</footnote>
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addition of earth-abundant metallic co-catalyst. The features such as bifunctional mechanism and electronic effect, intended from this design, involve the catalytic activity enhancement of the electrode material.[20] Cerium (Ce) is a Rare Earth (RE) element that has CeO₂ as the main oxide, and has been widely employed as catalyst and/or co-catalyst to enhance the catalytic performance of various of materials.[21,22] Ce is stable in alkaline environment and has abundant oxygen vacancy, high oxygen storage capacity, high oxygen mobility, conductivity, and high surface area, not to mention that transition between CeⅢ/CeⅣ redox pair is easy. Together, these characteristics improve charge transfer and adsorption of specific intermediates during electrochemical reactions.[23-25] Modifying Pt catalysts with Ce has been shown to improve the electrocatalytic activity of materials for the electro-oxidation of alcohols such as methanol and ethanol, both in acidic and alkaline media.[25-30]

This investigation aims to study the electrochemical valor-
ization of glycerol in an Alkaline Direct Glycerol Fuel Cell
operating in batch mode at room temperature, to co-generate
clean electrical energy and value-added electro-oxidation
products by using Ce-modified Pt-based electrocatalysts with
low Pt loading.[31] The electrocatalysts were synthesized by the
Bromide Anion Exchange (BAE) method, while the main
compounds issued from the anodic glycerol conversion were
identified by spectroscopic (in situ FTIR) and spectrometric (LC-
MS) techniques.

**Results and discussion**

Physico-chemical characterizations

The XRD patterns of the as-prepared materials from the BAE method (Figure S1) for this study are shown in Figure 1. However, the physical characterization showed that the samples consisted of the CeO₂ phase instead of metallic Ce. Therefore, all materials are re-designated as CeO₂ (to denote Ce) and PtCeO₂/C (to denote PtCe/C). The peak around 2θ = 25° was due to the (002) phase of the carbon Vulcan XC-72R hexagonal structure. The peaks at 2θ = 40, 46, 67.7, 81, and 86° were related to the (111), (200), (220), (311), and (222) crystallographic planes of the Pt face-centered cubic (fcc) crystalline structure (JCPDS #04-0802).[32] The peaks at 2θ = 28.46, 33, 47.3, and 56° correspond to the (111), (200), (220), and (311) crystallographic planes of CeO₂ (JCPDS #65-5923).[33] The PtCeO₂/C diffraction pattern does not show any significant peak displacement, indicating that the bimetallic catalyst consists of Pt nanoparticles decorated with vicinal CeO₂ particles.

TGA analysis for Pt/C (Figure S2) and the ICP-OES analysis for PtCeO₂/C showed the metal loading percentages of 19 wt%, and 18 wt%, respectively, which was an excellent agreement with the nominal composition (20 wt%) and indicated that the synthesis effectively yields reduced metals supported on carbon. Furthermore, ICP-OES analysis allowed the percentage by mass of each metal to be quantitatively determined. For the PtCeO₂/C electrocatalyst, the Pt:Ce ratio was 52:48 wt%, close

<figure><img src="image_5.png" /><figcaption>Figure 1. XRD patterns of the BAE-synthesized Pt/C (black line), Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C (red line), and CeO<sub>2</sub>/C (blue line) catalysts.</figcaption></figure>
to the initially planned 50:50 wt%. These results are summarized in Table 1.

Figure 2 shows the TEM images (a, b and d) and the histogram (c and e) for the BAE-synthesized Pt/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts. Figure 2a indicated that the Pt nanoparticles (black points) were well distributed on the carbon support (gray cloud-like structures) with few regions of agglomeration. Figure 2b allowed interspatial distance (lattice parameter) equal to 0.28 nm to be identified in the planes of one particle, which is characteristic of the Pt face-centered cubic (fcc) unit cell.[34] Particle size ranged from 2.40 to 9.40 nm and the average size distribution calculated by Gaussian fit was 5.21 ± 0.24 nm (Figure 2c).

Figure 2d presents the Pt and CeO₂ nanoparticles distribution. A mixture behavior was noted: a lattice parameter resembling that of the Pt/C electrocatalyst (0.28 nm) was seen, due to the Pt fcc structure.[35,36] The histogram of this electrocatalyst showed that particle size distribution ranges from 1.70 to 10.80 nm, with average size distribution of 5.38 ± 0.09 nm (Figure 2e). In PtCeO₂/C, CeO₂ particles are either isolated on the carbon support or form clusters on which small Pt particles are observed (Figures 2d and 2f). EDS analysis and mapping images (Figures 2d, 2f, S3 and S4) show the presence of Pt, Ce and O in the composition of this bimetallic catalyst. Although some zones are richer in Pt or CeO₂ than others. STEM images from HAADF analysis (Figure 2f and 2g), showed some zones richer in Pt or CeO₂ than others; they reveal that Ce–O bond can also be seen in Figure S3b, which confirms the XRD characterization measurements.[27,36, 37] These observations suggest, without any evidence of alloyed particles, that Pt and CeO₂ are strongly interacting in the material; this will be helpful in explaining the improvement of the electrocatalytic activity in the PtCeO₂/C material during the glycerol oxidation reaction.

## Electrochemical measurements

Figure 3a illustrates the cyclic voltammogram (CV) of the Pt/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts in the GOR in alkaline medium. In the absence of glycerol, the hydrogen adsorption/desorption region (–850 and –500 mV vs Hg|HgO),[38] and the oxidation/reduction of Pt to PtO (–200 and 300 mV vs Hg|HgO)[39] are observed. The ECSA values of 66.9 and 111.6 m² g<sub>pt</sub><sup>–1</sup> were respectively determined for the Pt<sub>100</sub>/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts from the CV obtained by CO-stripping (Figures 3b and S5). The ECSA calculated for the

electrocatalyst modified with ceria was the double than in the case of Pt/C, where the catalytic activity increased given that the modified electrocatalyst had 50% less Pt mass loading and still maintained the current density magnitude for the CO oxidation process. Li et al.[40] observed a similar behavior for Ce-modified Pt catalysts supported on carbon nanotubes.

In the presence of 0.5 M glycerol (Figure 3c), one observes the suppression of hydrogen adsorption/desorption peaks because the available Pt active sites were occupied by adsorbed glycerol or intermediates.[41] As pointed out above, reducing the Pt amount in the electrocatalyst by 50 wt% Pt/C modification with CeO₂ increased the electrocatalytic mass activity, and the maximum current density (j<sub>max</sub>) changed from 80.3 to 281.5 mA g<sub>pt</sub><sup>–1</sup>. The oxidation of glycerol occurs at ca. –0.4 V vs Hg|HgO, both on Pt/C and on PtCeO₂/C during forward scan. Since the current density has been increased 3.5 times without any shift in the peak potential, it can be stated that the glycerol oxidation reaction is promoted by the surface structuring effect due to the presence of CeO₂. However, given the proximity of the Pt and CeO₂ sites, the presence of adsorbed oxygenated species at low potentials, provided by CeO₂, could contribute to a better activity of PtCeO₂/C through bifunctional mechanism,[2,25,27,42–44] as represented in Eq. 1.[45] The role played by the Pt active sites was clarified by confirming that the CeO₂/C anode was inactive for GOR (Figure S6).

$$CeO_2 + OH^- \rightarrow CeO_2-OH_{ads} + e^- \quad (1)$$

The re-oxidation peaks that emerged in the backward scan (cathodic path for both electrocatalysts) can be explained by restructuring/rearrangement of the surface oxides formed during the glycerol oxidation anodic sweep, making new active sites available. This important activity, albeit of lesser intensity, such that Pt and CeO₂ mutually aid each other by bifunctional catalysis, thanks to the formation/desorption of (hydro)oxide species.[46,47] The sharp peak at around 0.2 V vs Hg|HgO is included in the glycerol re-oxidation region. This peak, already obtained in the same potential range during ethanol oxidation on PtSnNi,[48] could be due either to the desorption of a species during the surface restructuring of the catalyst, or to the perturbation of the surface by the formation of oxygen bubbles on the co-catalyst sites, as CeO₂ acts as an oxygen pump. Moving forward in the electrochemical analysis, Figure 3d presents the chronoamperometric profile (CA) in the presence of 0.5 M glycerol set at a fixed potential (–0.2 V vs Hg|HgO) for 30 min. The CA and CV data agreed and indicated that the

<table><caption>**Table 1.** TGA*, ICP-OES**, XRD and TEM results for the prepared electrocatalyst.</caption><thead><tr><th>Electrocatalyst</th><th>Experimental (wt%)</th><th>Results</th><th></th><th></th><th></th></tr><tr><th>Nominal (wt%)</th><th></th><th>Phase</th><th>2θ/°</th><th>D<sub>XRD</sub>/nm</th><th>D<sub>TEM</sub>/nm</th></tr></thead><tbody><tr><td>Pt<sub>20%</sub>/C</td><td>Pt<sub>19%</sub>/C</td><td rowspan="2">Pt</td><td>39.75</td><td>5.8</td><td>5.21</td></tr><tr><td>(Pt<sub>50%</sub>Ce<sub>50%</sub>)<sub>20%</sub>/C</td><td>(Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>)<sub>18%</sub>/C</td><td>39.83</td><td>5.2</td><td>5.38</td></tr><tr><td colspan="2">D<sub>XRD</sub> is the crystallite size</td><td colspan="3">*TGA for monometallic material</td></tr><tr><td colspan="2">D<sub>TEM</sub> is the particle size</td><td colspan="3">**ICP-OES for bimetallic material</td></tr></tbody></table>
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 2.** TEM images of the BAE-synthesized Pt/C (a-b) and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C (d) catalyst; histogram of the particle size distribution of Pt/C (c) and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C (e); elemental mapping of Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C (f), and STEM image of the Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C catalyst (g).</figcaption></figure>

Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalyst was more active than Pt/C for the GOR generating higher current density throughout the analyses. Charge increased by 54% upon addition of Ce to the Pt/C electrocatalyst.

ECSA values of 12.7 and 11.2 cm² were respectively determined for the Pt<sub>100</sub>/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts from the CV obtained by CO stripping (Figures 3b and S5). The calculated values were not normalized by the Pt mass in the electrode because the Pt mass loading in the catalysts was different, reinforced by the fact that Ce was not active for

oxidizing CO, but acted to promote oxygenated species adsorption on the active sites, to improve the electrocatalytic activity, as explained above. Although the ECSA calculated for the electrocatalyst modified with cerium was slightly lower than in the case of the Pt/C electrocatalyst, the electrocatalytic activity still increased given that the modified electrocatalyst had 50% less Pt mass loading and still maintained the current density magnitude for the CO oxidation process. In an alkaline medium, the electrooxidation of CO to CO<sub>2</sub> is accompanied by a non-electrochemical carbonate reaction (Eqs. S1–S5).
<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /><figcaption>**Figure 3.** (a) Cyclic voltammograms of Pt/C (19 wt% and 0.1 $mg_{Pt} cm^{-2}$) and $Pt_{52}(CeO_{2})_{48}/C$ (18 wt% and 0.05 $mg_{Pt} cm^{-2}$) in 0.1 M NaOH recorded at 10 $mV s^{-1}$. (b) CO-stripping CV profiles of Pt/C and $Pt_{52}(CeO_{2})_{48}/C$ in 0.1 M NaOH recorded at 10 $mV s^{-1}$. (c). Cyclic voltammograms of Pt/C (19 wt% and 0.1 $mg_{Pt} cm^{-2}$) and $Pt_{52}(CeO_{2})_{48}/C$ (18 wt% and 0.05 $mg_{Pt} cm^{-2}$) in 0.1 M NaOH in the presence of 0.5 M Glycerol electrolyte solution recorded at 10 $mV s^{-1}$. (d) Chronoamperometry at -0.2 V vs. Hg | HgO (0.7 V vs. RHE) for 30 min in 0.1 M NaOH + 0.5 M Glycerol.</figcaption></figure>

## Fuel Cell (FC) performance and glycerol electro-oxidation products

The system was connected in the fuel cell mode as exhibited in Figure S7. Figure 4a illustrates the polarization and power density curves obtained after the glycerol fuel cell was operated for 4 h. A typical polarization curve profile emerges for both electrocatalysts studied here, and two regions can be highlighted: (I) activation/polarization region at low current densities and (II) ohmic drop polarization region starting at 0.2 $mA cm^{-2}$.[49,50] (Figure S8). Both electrocatalysts provided the same open circuit voltage (0.600 ± 0.004 V). However, in the fuel cell testing with $Pt_{52}(CeO_{2})_{48}/C$ as the anode, the maximum power density was 0.26 $mW cm^{-2}$ at 1.2 $mA cm^{-2}$ against 0.20 $mW cm^{-2}$ at 1.0 $mA cm^{-2}$ for the cell operating with Pt/C as the anode, an improvement of 30% in the generated electrical energy (Figure 4a).

Figure 4b depicts the measured single potentials for the cathode and anode during the cell operation (Figures S9, S10 and S11). The PdFe/C cathode did not limit the cell operation; in fact, it was relatively stable during operation for 4 h, as reported recently.[51] Concerning the ORR at the PdFe/C electro-catalyst, the potential shifted slightly as a function of the cell operation ($ΔE_{CATHODE}$ = 32 mV). On the other hand, the GOR deactivated the cell in the case of both electrocatalysts. The OCP for the Pt/C and $Pt_{52}(CeO_{2})_{48}/C$ catalysts were 0.333 V and 0.294 V vs RHE, respectively. As the GOR proceeded, the anodic potentials increased linearly ($ΔE_{Pt}$ = 521 mV, $ΔE_{PtCe}$ = 568 mV). This limitation could be due to the complexity of the organic reactions taking place on the electrocatalysts surface.

The glycerol electro-oxidation products were identified and quantified by HPLC. An RID detector was used to follow the glycerol concentration, and a UV-Vis detector was employed to extract data about the products.[52] Figure S12 shows the
<figure><img src="image_10.png" /><figcaption>Figure 4. (a) Fuel Cell polarization curves with Voltage (left axis) and power density (right axis) for cell operating with the Pt/C (black) or Pt$_{52}$(CeO$_{2}$)$_{48}$/C (red) electrocatalysts as anode. (b) Polarization curves following the electrode potentials separately in the analyses. Anode material: Pt/C (0.38 mg$_{Pt}$ cm$^{-2}$) or Pt$_{52}$(CeO$_{2}$)$_{48}$/C (0.19 mg$_{Pt}$ cm$^{-2}$) in 0.1 M NaOH + 0.1 M Glycerol. Cathode material: Pd$_{0.88}$Fe$_{0.15}$/C (0.32 mg$_{Pd}$ cm$^{-2}$) in 0.1 M NaOH + O$_{2}$. Fumatech AEM. Fuel Cell operated at 25 ± 1 °C.</figcaption></figure>

chromatograms obtained after 4 h of DGFC operation. Five electro-oxidation products emerged, namely oxalate, tartronate, glycerate, glycolate, and formate, with retention times of 6.8, 8.0, 11.2, 13.0, and 14.4 min, respectively, as shown in Figure S12. Glycerol and its electro-oxidation products were quantitatively analyzed, and the results are summarized in Table 2. For the Pt/C electrocatalyst, glycerate was the main oxidation product, with 65% of selectivity, as calculated by Eq. 2. Also, 15.1 mmol L$^{-1}$ (14%) of glycerol electroconversion was achieved after the cell was operated for 4 h. Besides the energy that was generated, value-added products were obtained, e.g., 428 µmol L$^{-1}$ cm$^{-2}$ min$^{-1}$ mg$_{Pt}$$^{-1}$ (Eq. 3) for glycerate which represented 4 moles of electrons per mole of the electro-oxidized glycerol. Moving forward, and when Pt$_{52}$(CeO$_{2}$)$_{48}$/C electrocatalyst was used, the main electro-oxidation product was also glycerate, but at lower selectivity (41%), nevertheless, other value-added products were obtained in higher yields, including glycolate (10%) and formate (8%) (Table 2). Although the Pt$_{52}$(CeO$_{2}$)$_{48}$/C electrocatalyst was less selective for glycerate

and the glycerol electroconversion rate (6%) was lower when compared to the Pt/C electrocatalyst, the formed converted glycerol to more oxidable products, raising the number of electrons per mole of electro-oxidized glycerol (5 for glycolate and 8 for formate). This explained why the former electro-catalyst generated higher energy.

$$ Selectivity (\%) = \frac{1}{v_i} \times \frac{C_{i,t}}{C_{ge}} \times 100 ; \qquad (2) $$

where $v_i$ is the electrooxidation product stoichiometric coefficient; and $C_{it}$ is the concentration of the product i formed as a function of time (in mol L$^{-1}$) and $C_{ge}$ is the electroconverted glycerol concentration (in mol L$^{-1}$).

$$ Production rate (\mu mol \cdot L^{-1} \cdot cm^{-2} \cdot min^{-1} \cdot mg_{Pt}^{-1}) = \frac{C_{i,t}}{A_{geo} \times t \times m_{Pt}} ; \qquad (3) $$

where $C_{ij}$ is the concentration of the electrooxidation product i formed as a function of time (µmol·L$^{-1}$), $A_{geo}$ is the anode geometric area (cm$^2$), t is the reaction time (min) and $m_{Pt}$ is the mass of Pt on the anode catalyst (mg).$^{[53]}$

Figure 5 shows that glycerol oxidation on Pt$_{52}$(CeO$_{2}$)$_{48}$/C is less selective towards glycerate but produces more C–C bond cleavage molecules with C2 (glycolate) and C1 (formate).$^{[1]}$ The presence of CeO$_{2}$ in the catalyst contributes to a higher power density in the DGFC (Figure 4a). The C3/C2 ratio also indicates that selectivity will tend to increase when glycerol oxidation leads predominantly to glycerate and tartronate (C3). The Pt/C and Pt$_{52}$(CeO$_{2}$)$_{48}$/C electrocatalysts gave C3/C2 ratios of 6 and 2.7, respectively. One may conclude that Ce has poison-resistant properties, which facilitated the formation and removal of intermediates from the surface of Pt active sites, leading to the generation of more oxidizable products.$^{[54]}$ The formation of each compound resulting from electrochemical oxidation of glycerol is represented by equations S6–S12. As oxidation products, carbonate ions (bands of CO$_{2}$ and CO$_{3}$$^{2-}$) must be considered because they are determined qualitatively by *in situ* FTIRS (see next section).

Glycerol electrooxidation begins with the dehydrogenation of the OH groups at the primary (α-carbon) or secondary (β-carbon) carbon, to form alkoxides, respectively, glyceraldehyde or dihydroxyacetone.$^{[5]}$ In alkaline medium, abundant of OH$^{-}$ produces Pt-OH$_{ads}$, which can subsequently oxidize the chemisorbed glyceraldehyde into glycerate, following the Cannizzaro reaction,$^{[18]}$ explaining why no glyceraldehyde was detected during chromatographic analyses.

The cross-over rates for both DGFC were also evaluated (Eq. S13), which consisted in checking the concentration of glycerol that crossed the alkaline exchange membrane to the cathodic compartment at the end of the cell operation for 4 h.$^{[55]}$ For Pt/C or Pt$_{52}$(CeO$_{2}$)$_{48}$/C as the electrocatalysts, the cross-over rate was 28 and 40 µmol L$^{-1}$ cm$^{-2}$ min$^{-1}$, respectively. Nevertheless, when the cathode polarization curves for both DGFCs in Figure 4b was analyzed, the electrocatalytic activity of PdFe/C electrocatalyst remained constant, hardly harming the
<figure><img src="image_11.png" /></figure>

<table><caption>**Table 2.** 4 h-Fuel Cell operation for 0.1 M glycerol in 0.1 M NaOH.</caption><thead><tr><th>Catalyst</th><th>GE (mmol L<sup>-1</sup>)</th><th colspan="5">Reaction products (mmol L<sup>-1</sup>)</th></tr></thead><tbody><tr><td rowspan="4">Pt/C</td><td rowspan="4">15.1</td><td><strong>Glycerate</strong></td><td>Tartronate</td><td>Oxalate</td><td>Glycolate</td><td>Formate</td></tr><tr><td>9.75</td><td>0.42</td><td>0.26</td><td>1.44</td><td>1.47</td></tr><tr><td><strong>Selectivity (%)</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>64.5</td><td>2.8</td><td>1.1</td><td>6.4</td><td>3.2</td></tr><tr><td></td><td></td><td><strong>Production rate (µmol L<sup>-1</sup> cm<sup>-2</sup> min<sup>-1</sup> mg<sub>Pt</sub><sup>-1</sup>)</strong></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>427.6</td><td>18.5</td><td>11.3</td><td>63.3</td><td>64.6</td></tr><tr><td rowspan="4">PtCeO<sub>2</sub>/C</td><td rowspan="4">6.9</td><td><strong>Glycerate</strong></td><td>Tartronate</td><td>Oxalate</td><td>Glycolate</td><td>Formate</td></tr><tr><td>2.83</td><td>0.12</td><td>0.07</td><td>1.01</td><td>1.73</td></tr><tr><td><strong>Selectivity (%)</strong></td><td></td><td></td><td></td><td></td></tr><tr><td>40.6</td><td>1.7</td><td>0.7</td><td>9.6</td><td>8.3</td></tr><tr><td></td><td></td><td><strong>Production rate (µmol L<sup>-1</sup> cm<sup>-2</sup> min<sup>-1</sup> mg<sub>Pt</sub><sup>-1</sup>)</strong></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>247.9</td><td>10.6</td><td>6.1</td><td>88.2</td><td>152.1</td></tr></tbody></table>

GE: glycerol electroconversion

<figure><img src="image_12.png" /><figcaption>**Figure 5.** Value-added glycerol electro-oxidation product selectivity in alkaline medium. Pt/C as anode: more selectivity for glycerate (chemical equation at left). Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C as anode: more energy produced per mol of oxidized glycerol (chemical equation on the right).</figcaption></figure>

ORR. No detectable amount of glycerol electro-oxidation products was identified in the cathodic compartment.

Mass spectrometry confirmed the results obtained during the chromatographic analyses. The spectra in Figure S13 and Figure S14, recorded in the negative mode, displayed peaks

with mass-to-charge ratio (m-1/z) values operating at the negative mode of 75, 89, 91, and 105, respectively related, to glycolic acid, oxalic acid, glycerol, and glyceric acid molecular ions. The peak at 118 (m-2/z) was due to tartronic acid, attributed to double deprotonation of this molecule to form a
<figure><img src="image_13.png" /></figure>

tartronate ion.[56] The mass spectra of compounds obtained from standard solutions are shown in Figure S14. Formic acid could not be detected – its m/z ratio is equal to 46 but the lower limit of detection of the equipment is m/z = 50; moreover, this molecule was added at 0.01 wt% to water to mitigate the fragmentation of the reaction products in negative mode.

## In situ Fourier-Transform infrared spectroscopy (FTIR) analyses coupled with Electrochemical Measurements

To identify the glycerol electro-oxidation intermediates and products, spectroelectrochemical experiments were performed. Figure 6a and Figure 6c exhibit interferograms of single potential alteration infrared reflectance spectroscopy (SPAIRS) for the Pt/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts during the glycerol electro-oxidation. The band at 1394 cm<sup>-1</sup> point out that carbonate (CO<sub>3</sub><sup>2-</sup>) started to emerge at lower potential (300 mV vs RHE). This band remained up to about 800 mV vs RHE, where a band shift towards 1358 cm<sup>-1</sup> is noticed. This change coincided with the appearance of a thin and intense band at 2343 cm<sup>-2</sup> attributed to carbon dioxide (CO<sub>2</sub>). At higher

potentials (E > 0.8 V vs RHE) glycerol electro-oxidation in the thin solvent layer on the electrode-IR window interface produced H<sub>3</sub>O<sup>+</sup> (hydronium ion) on the electrode surface. The H<sub>3</sub>O<sup>+</sup> concentration in the thin layer of the electrolyte cannot immediately react with OH<sup>-</sup>, reducing the local pH and converting the carbonate ion to CO<sub>2</sub>.<sup>[57-59]</sup> Additionally, at about 550 mV vs RHE, a band at 1580 cm<sup>-1</sup>, corresponding to the formation of carboxylate groups such as glycerate and/or tartronate on the surface of the Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalyst surface. Figure S14 shows further evidence of glycerol oxidation on Pt/C without forming carbonate ions. Moving forward, Figure 6b and Figure 6d show the spectra recorded during CA experiments (30 minutes) at different potentials (0.5, 0.6, 0.7, 0.8, and 0.9 V vs RHE) for Pt/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C as electro-catalysts. In both cases, glycerate (1109 cm<sup>-1</sup> for Pt/C and 1110 cm<sup>-1</sup> for Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C), oxalate (1306–1307 cm<sup>-1</sup>), glycolate (1074 cm<sup>-1</sup>) and formate (1353–1360 cm<sup>-1</sup>) were identified as reaction products resulted from electro-oxidation of glycerol. The bands at 1578–1581 cm<sup>-1</sup> were related to carboxylate groups from glycerate and/or tartronate, while those between 1360 and 1390 cm<sup>-1</sup> were issued from the carbonyl group (C–O) stretching. Furthermore, the positive bands at 1046–

<figure><img src="image_14.png" /><figcaption>**Figure 6.** (a) and (c) SPAIR spectra recorded at 1 mV s<sup>-1</sup> between 50 and 1200 mV vs. RHE. (b) and (d) FTIR spectra recorded during chronoamperometry at 0.5 V to 0.9 V vs. RHE for 30 min on the Pt/C and Pt<sub>52</sub>(CeO<sub>2</sub>)<sub>48</sub>/C electrocatalysts in 0.1 mol L<sup>-1</sup> NaOH electrolyte + 0.1 mol L<sup>-1</sup> of glycerol.</figcaption></figure>
<figure><img src="image_15.png" /></figure>

1047 cm⁻¹ and 2699–2694 cm⁻¹ were assigned to OH⁻ and glycerol consumption during the reactions, and the bands at 3679–3687 cm⁻¹ were ascribed to the stretching of water molecules.[57,59–61]

## Conclusions

Here, glycerate was produced as the main value-added product from glycerol electro-oxidation in alkaline medium in a Fuel Cell operating in the batch mode at room temperature. As anodes with low Pt-loading (wt%), two nanostructured electrocatalysts – Pt/C, and Pt₅₂(CeO₂)₄₈/C – investigated herein successfully synthesized by the BAE method were tested. Efforts were made with this synthesis approach to decrease the precious metal loading at ca. 20 wt%, while in the second electrode material a Rare Earth element (under CeO₂ phase) as co-catalysts contributed to reduce at 50% the PGM amount. An improvement in the electrocatalytic activity was observed for the latter electrocatalyst, with provided higher degree of glycerol electro-oxidation and generated more energy when it was applied as the anode in a DGFC. In terms of cogeneration (fuel cell and electrosynthesis), Pt/C electrocatalyst was more selective to a glycerol-to-glycerate conversion at 65%. However, the bifunctional mechanism taking place in the presence of CeO₂ helped to explain the improved electrocatalyst of PtCeO₂/C: Ce adsorbed oxygenated species for either promoting the glycerol oxidation or releasing the intermediate species. Regarding the cogeneration proposal, glycerate was well identified by in situ FTIRS and LC-MS as value-added product on Pt/C, while Pt₅₂(CeO₂)₄₈/C as anode was more active to promote higher power density in a DGFC.

## Experimental section

### Synthesis of the Pt-based electrocatalysts by the BAE method

Developed and optimized by the Kokoh's group,[59,62–66] the “Bromide Anion Exchange” (BAE) method is a clean and surfactant-free one-pot green process which allows obtaining carbon-supported Pt nanoparticles (Pt/C) (Figure S1). Briefly, in a two-necked round-bottom glass, appropriate amounts of the metal precursors hexachloroplatinic(IV) acid hexahydrate (H₂PtCl₆·6H₂O, with about 40% Pt purchased from Sigma-Aldrich) and, in the case of the bimetallic preparation, cerium(III) chloride (CeCl₃, 99.9% purity, purchased from Alfa Aesar) were solubilized in ultra-pure water (Milli-Q® Millipore, 18.2 MΩ cm at 20 °C), followed by the addition of potassium bromide (KBr, 99% purity, purchased from Alfa Aesar) at a previously decided proportion φ = n(Br⁻)/n(Metal), where n is the number of moles of each component. The bromide anion (Br⁻) solubilized in the solution replaced the counter ion in the metallic aqua-complex, to provide a steric environment that acted as a capping agent helping to stabilize the metallic nanoparticles to be generated in the next step of the synthesis. To ensure the replacement, about five times excess was used (φ = 5.5).[67] Counter-ion substitution slightly changed the yellowish color of the initial [PtCl₆]²⁻ solution due to the replacement of Cl⁻ by Br⁻, generating [PtCl₆·xBrₓ]²⁻ complex, where 0 ≤ x ≤ 6[68] was formed according to Eq. 4:

$$ 
\begin{align} 
2\text{H}^{+}_{(\text{aq})} + [\text{PtCl}_6]^{2-}_{(\text{aq})} + 6\text{K}^{+}_{(\text{aq})} + 6\text{Br}^{-}_{(\text{aq})} &\rightarrow \nonumber \\ 
2\text{H}^{+}_{(\text{aq})} + [\text{PtBr}_6]^{2-}_{(\text{aq})} + 6\text{K}^{+}_{(\text{aq})} + 6\text{Cl}^{-}_{(\text{aq})}; \tag{4}
\end{align} 
$$

After the solution color changed, Carbon Vulcan XC72R (purchased from Cabot and previously treated under N₂ atmosphere at 400 °C for 4 h) was added, and the mixture was left in ultrasonication bath for 45 min to ensure that carbon support was completely suspended. To obtain nanoparticles, the metallic center of the complex was reduced by adding, under vigorous stirring, 0.1 M sodium borohydride (NaBH₄ ≥ 98.0% purity, purchased from Sigma-Aldrich) solution in large excess as compared to the number of moles of the previously added metal(s) ∝ = n(NaBH₄)/n(Metal), where α was fixed to 15 as previously reported.[57] After that, the temperature was set to 40 °C and kept at this value for 2 h. Finally, the resulting electrocatalyst was filtered through a Millipore membrane (Millipore Express® Plus, 0.22 µm PES Membrane, Hydrophilic purchased from Merck Group), under reduced pressure; washed thoroughly with ultra-pure water and absolute ethanol and dried in an oven at 40 °C for 24 h.

### Physico-chemical characterizations

The metal loading (wt%) on Pt/C monometallic catalyst was checked by thermogravimetric analysis (TGA), from room temperature to 900 °C at 10 °C.min⁻¹ under synthetic air atmosphere: TA Instruments 2960/Q600 SDT analyzer was used. Pt₅₂(CeO₂)₄₈/C bimetallic catalyst was analyzed by inductive coupled plasma optical emission spectroscopy (ICP-OES) to quantify the metal loading and the Pt/CeO₂ mass ratio percentage in the electro-catalyst. To this end, PtCeO₂/C was solubilized in acidic solution (3 mL of > 68% HNO₃ and 5 mL of 34–37% HCl) and heated in a Multiwave Pro from Anton Paar microwave oven. After that, the solution volume was completed to 50 mL with ultra-pure water, and the sample was analyzed (four replicates) on an Agilent 5110 VDV ICP-OES device.

The structure of the Pt-based electrocatalyst was analyzed by X-Ray Diffraction (XRD) fixed parameters were used 2θ range from 10 to 100° and step of 0.025° s⁻¹. The diffractograms were recorded on a Malvern Panalytical EMPYREAN diffractometer operating with a Cu Kα radiation (λ = 0.15406 nm) source generated power of 45 kV and 40 mA. The Pt(111) phase diffraction peak was used to calculate the average crystallite sizes according to the Scherrer equation (Eq. 5):

$$ D_{hkl} = \frac{K\lambda}{B_{hkl}cos\theta}; \tag{5} $$

where D_hkl is the crystallite size, hkl are the Miller indexes, K is the crystallite-shape factor being 0.9 an acceptable approximation for cubic crystalline systems, B_hkl is the full-width at half-maximum (FWHM) of the diffraction peak in radians, and θ is the Bragg angle.[69,70]

Size, spatial distribution, and morphology of the nanocatalysts were obtained using Transmission Electron Microscopy (TEM) performed in a JEOL JEM-2200FS equipment, operating in bright field mode at 200 kV (FEG source), coupled with an energy-dispersive X-ray spectrometer with a Bruker QUANTAX detector (30 mm² SiLi), to perform energy-dispersive X-ray spectroscopy (EDS) analysis. Compositional EDS maps were acquired using a Bruker detector (XFLOSAH6/60) and data was processed with Esprit 2.1 software. Scanning Transmission Electron Microscopy (STEM) analyses were conducted on Bruker QUANTAX device operated at 200 kV. A nanoprobe (~1 nm) was used to obtain STEM HAADF imaging. In
this mode, electrons are detected at wide angles using a HAADF (High Angle Annular Dark Field) detector, providing an image with atomic number-dependent contrast (high-Z region in clear on the STEM-HAADF image and vice versa). The analyzed samples of the catalyst powder were well dispersed in ethanol under ultrasound irradiation. The resulting suspension was then deposited onto a carbon-coated copper TEM grid (300 mesh) and dried.

## Electrochemical measurements

Cyclic voltammetry and chronoamperometry analyses were carried out using a three-electrode cell connected to an Autolab Potentiostat (PGSTAT302N from Metrohm AG) manipulated with the Nova 2.1 software. A 5 mm glassy carbon disk (0.196 cm²) inserted in a Teflon® rod was used as the working electrode, where 5 µL of catalytic ink was deposited (0.1 mg$_{Pt}$ cm⁻² for Pt/C and 0.05 mg$_{Pt}$ cm⁻² for Pt$_{52}$(CeO$_{2}$)$_{48}$/C). The catalytic ink was prepared by adding 4 mg of catalyst in 190 µL of isopropanol (≥ 99.9% purity, purchased from VWR Chemicals BDH®) and 10 µL of Nafion® solution (perfluorinated resin solution, 5 wt% in lower aliphatic alcohols and 15–20% of water, purchased from Sigma-Aldrich). The ink was maintained in ultrasonic bath for 30 min. After a stable and homogeneous emulsion was obtained, the fresh ink was deposited on a well-polished glassy carbon surface and dried at room temperature. A 1.5 cm² glassy carbon plate was used as the counter electrode and a 0.1 M NaOH Hg|HgO electrode was employed as the reference electrode connected to the electrolyte by a Luggin capillary tip. All the analyses were accomplished at room temperature in an alkaline electrolyte (0.1 M NaOH solution prepared immediately before use from a NaOH standard solution (50% in H$_{2}$O), purchased from Sigma-Aldrich). The glycerol (ACS reagent, ≥ 99.5% purity, purchased from Sigma-Aldrich) concentration was fixed at 0.5 M. Before analysis dissolved oxygen was eliminated by bubbling nitrogen (N$_{2}$, ≥ 99.995% purity, from Air Liquide) into the electrochemical cell.

The electrochemical active surface area (ECSA) of the catalysts was determined by CO stripping voltammetry using carbon monoxide (CO) was employed as a probe molecule. For this purpose, CO (N47 ≥ 99.997% purity, from Air Liquide) was bubbled into the cell for 10 min, maintaining the working electrode was kept polarized at 0.3 V vs. RHE. After that, the excess CO was removed by bubbling

N$_{2}$ (30 min). Stripping cyclic voltammetry between the 50 mV and 1200 mV vs RHE at 10 mV s⁻¹ was performed twice, the first was performed to check the CO oxidation to CO$_{2}$, whereas the second was performed to confirm that all adsorbed CO was oxidized. CO stripping provides ECSA measurement by comparing the experimental CO charge (Q$_{CO}$) with the theoretical value (QtheoCO) of 420 µC cm⁻² for CO-adsorbed monolayer on polycrystalline Pt surfaces,[71,72] as shown in Eq. 6:

The second stripping cycle was used as linear background to extract the Q$_{CO}$ by integrating the oxidation peak in the first voltammetry cycle.

$$ \text{ECSA (cm}^2\text{)} = \frac{Q_{\text{CO}}(\mu\text{C})}{420 (\mu\text{C cm}^{-2})}; \qquad (6) $$

The Q$_{CO}$ can be obtained from the stripping voltammogram of CO oxidation to CO$_{2}$ by using Eq. 7:

$$ Q_{\text{CO}} = \frac{1}{v} \times \int i(E)dE; \qquad (7) $$

where v is the linear potential scan rate (V s⁻¹), i is the current (A) and E is the electrode potential (V). The integration shown above was calculated from the stripping voltammogram by using the Origin® 9/2020 software (from OriginLab Corporation).

## Direct Alkaline Fuel Cell performance for glycerol electro-oxidation

Glycerol was electro-oxidized in a homemade two-compartment Teflon® cell (Figure 7) at 25 °C; an anion exchange membrane (AEM, Fumasep FAA, purchased from Fumatech) was employed. This anion conducting membrane was previously treated in alkaline medium as described in the Supporting Information. The membrane induces OH⁻ anions to diffuse from the cathode to the anode during cell operation.[16] The anode was prepared by depositing 50 µL of catalytic ink onto both sides of 0.25 cm² carbon paper (Toray Carbon Paper 090, purchased from Fuel Cell Store). The total amount of electrocatalyst was 0.38 mg$_{Pt}$ cm⁻² for Pt/C and 0.19 mg$_{Pt}$ cm⁻² for PtCeO$_{2}$/C. A homemade Pd$_{85}$Fe$_{15}$/C cathode with

<figure><img src="image_16.png" /><figcaption>Figure 7. Scheme of the Alkaline Direct Glycerol Fuel Cell (ADGFC) used for the bi-compartmentalized electro-oxidation studies.</figcaption></figure>
<figure><img src="image_17.png" /></figure>

0.32 mgPd cm⁻² was prepared as described above. Details about the synthesis and characterization of the cathode-catalyst are provided in Supporting Information (Figures S16, S17 and S18). A 2- or 4-electron ORR reaction pathway can be described by Eqs. S14–S17. The system was assembled and connected to a potentiostat to monitor the cell voltage (Cell voltage = E<sub>CATHODE</sub> – E<sub>ANODE</sub>), and multimeters were connected in each compartment to follow the cathode and anode potentials separately. For this, “BASi RE-6 Ag/AgCl reference electrode, MF-2078” purchased from Alvatek Ltd. (UK) was used as the reference electrode. Each compartment was filled with 25 mL of solution, the anode was filled with 0.1 M glycerol in 0.1 M NaOH solution, and the cathode was filled with 0.1 M NaOH. Gas was allowed to bubble through the system continuously, to provide oxygen for the cathodic reaction. Once assembled, the system was operated via Linear Sweep Voltammetry Galvanostatic (LSV-Galv) programmed to operate continuously for 4 h (galvano dynamic mode). After that, samples of the solution were collected from the anodic compartment to quantify the glycerol electro-oxidation products and from the cathodic side to check possible crossover through the AEM membrane.

## Identification and quantification of Glycerol Oxidation Reaction Products

After the Alkaline Fuel Cell was operated for 4 h, as described above, the glycerol electro-oxidation products were analyzed by HPLC on a Thermo Fisher UHPLC Dionex UltiMate 3000 device, at room temperature. An ion-exclusion Aminex® HPX-87H column (300 mm×7.8 mm, from BioRad) was employed, and the eluent solution was a 3.3 mmol L⁻¹ H₂SO₄ (98% purity, from Sigma-Aldrich). The products were run through the column in the isocratic mode at 0.6 mL min⁻¹. The system was equipped with an autosampler (Dionex ASI-100 Automated Sample Injector) with 20 µL sample loop. The separation system was connected to two detectors: a UV-Vis detector (λ= 210 nm/UVD170U, purchased from Dionex) and a Refractive Index detector (RID-IOTA2). The system was controlled with the Chromeleon™ 7 software. The retention times were obtained, and the products were quantified after obtaining a database from standard solutions (external calibration) and constructing analytical curves under the same conditions described above.

Mass Spectrometry hyphenated with HPLC Vanquish™ (from Thermo Fisher) at 35 °C (Vanquish™ oven, Thermo Fisher) was used to identify the products. The column was an ion-exclusion Repromer-H column (150 mm×8 mm, 9 µm, purchased from Chromservis) and the eluent solution consisted of ultra-pure water operating in the isocratic mode at 0.6 mL min⁻¹ in a 10-min run. The system was equipped with an autosampler (Vanquish™ Split Samplers operating at 4 °C, purchased from Thermo Fisher) with a 20 µL sample loop. The separation system was connected to an LTQ XL™ Linear Ion Trap Mass Spectrometer (from Thermo Fisher) operating in the negative mode. The system was controlled with the Xcalibur™ software, data were processed with the FreeStyle™ 1.8 SP2 software. The retention times were obtained and further product analysis by mass spectrometry was performed after a database was obtained from standard solutions prepared in ultra-pure water.

Sodium ions were removed from the electrolyte with a cationic exchange resin (Amberchrom® 50WX8, purchased from Sigma-Aldrich) by replacing Na⁺ for H⁺ (0.5 M H₂SO₄). Then, ultra-pure water was passed through the resin until neutral pH was reached. After that, organic compounds in water are suitable for injection into the MS system.[73]

## In situ Fourier-Transform Infrared Spectroscopy (FTIR) coupled with Electrochemical Measurements

Spectroelectrochemical analysis such as *in situ* FTIR is a powerful, sensitive, and robust tool to detect the intermediates and products formed during chemical reactions qualitatively. Measurement is made directly on the surface of the working electrode, where the reaction of interest takes place. *In situ* FTIR analyses were performed in a Vertex 80v spectrometer which was modified for beam reflection with angle incidence at 65° on the electrode surface. The detector consisted of an MCT HgCdTe (Mercury-Cadmium-Telluride) module previously cooled with liquid nitrogen (Air Liquide). The equipment can self-monitor the detector status and the vacuum system condition, to avoid vibration bands from the air. The FTIR spectra were recorded between 3900 and 900 cm⁻¹, the spectral resolution was 4 cm⁻¹. A three-electrode electrochemical cell was adapted to have a mid-infrared (MIR) transparent CaF₂ window. This electrochemical cell was cleaned as described in the SI for the glassware, but the CaF₂ window was cleaned just by using 50% of HNO₃ solution overnight and washed exhaustively with ultra-pure water. The counter electrode was a 2.5 cm² slab of glassy carbon, and a Reference Hydrogen Electrode (RHE) suitable for the alkaline medium was calibrated and used as the reference electrode (commercial Hydroflex® Hydrogen Reference Electrode purchased from Gaskatel GmbH). The working electrode was a previously polished 8 mm diameter glassy carbon disk onto which 10 µL electrocatalytic ink was deposited. The potentiostat was a compact Metrohm AG PGSTAT101 device. The experiments were carried out by Single Potential Alteration IR Spectroscopy (SPAIRS), which consists of acquiring spectra every 50 mV of potentiostatic sweep between 50 and 1200 mV vs RHE at 1 mV s⁻¹, and by FTIR/Chronoamperometry (E<sub>ap</sub> at different potentials for 30 min), to obtain a spectrum every 180 s. The working electrode was placed against the CaF₂ window (external reflection mode) to create a thin layer of solution between the electrode-electrolyte interface and to minimize signal loss from infrared absorption by the electrolyte. The reference (R₀) spectrum was measured at 50 mV vs RHE. The spectra presented in the interferogram correspond to the ratio between the spectrum at a specific potential and the reference spectrum (ΔR/R₀ = (R - R₀)/R₀), where R₀ is the reflectance to the reference spectrum, and R is the sample spectrum reflectance. Positive bands (R₀ > R) correspond to the consumption of species by attenuation of specific vibrations, and negative bands (R₀ < R) correspond to the formation of new species by increasing specific vibrations.

## Supporting Information

The authors have cited additional references within the Supporting Information[1,55,74–84]

## Author Contributions

Fabiano S. Cursi: Investigation, Methodology, Writing – original draft. Laurie Grimaud: Investigation, Methodology, review & editing. Julie Rousseau: Methodology, Investigation, review & editing. Dr. Karine Servat: Methodology, Investigation, Writing – review & editing. Dr. Claudia Morais: Methodology, Investigation, Writing – review & editing. Dr. Teko W. Napporn: Conceptualization, Supervision Methodology, Writing – review & editing. Prof. Adalgisa R. de Andrade: Conceptualization,
<figure><img src="image_18.png" /></figure>

Supervision, Writing – review & editing. **Prof. Kouakou B. Kokoh:** Conceptualization, Supervision, Writing – review & editing.

## Acknowledgements

The authors thank CAPES, CNPq, and Fapesp for financial support. This study was partly funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 and the Brazil-France CAPES/COFECUB program under project 88887.143104/2017-00. We acknowledged Fapesp for projects 2014/50924-4 and 2021/01134-7 and the National Council for Scientific and Technological Development (CNPq) for project INCT 465571/2014-0. The authors also kindly acknowledge the Pprime Institute (UPR3346 CNRS/ University of Poitiers) for providing access to the JEM 2200FS TEM. This work was partially financially supported by the CPER-FEDER program of the “Région Nouvelle Aquitaine”. Finally, thanks are due to S. Arri and L. Maziere (PLATINA – IC2MP) for the analyzes of XRD and ICP-OES, respectively, and C. Prado-Manso (DQ-FFCLRP-USP) for reviewing the English language of this text. This work pertains to the French government program “Investissements d’Avenir” (EUR INTREE, reference ANR-18-EURE-0010).

## Conflict of Interests

The authors declare no competing financial interests.

## Data Availability Statement

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

**Keywords:** alkaline direct glycerol fuel cell · cerium · glycerol electro-oxidation · glycerol valorization · Pt-based materials

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Manuscript received: October 27, 2023

Revised manuscript received: December 11, 2023

Version of record online: January 9, 2024