Promotional effect of auxiliary metals Bi on Pt,Pd, and Ag on Au,for glycerol electrolysis

In the search for active, stable, and selective electrocatalysts for glycerol electro-oxidation, this study focuses on the favorable effect that the addition of auxiliary metals, Bi for Pt and Pd, and Ag for Au, exerts on these three aspects. Electrocatalysts (Pt/C, Pt₃Bi/C, PtBi/C, Au/C, Au₃Ag/C, Pd/C and Pd₃Bi/C) were successfully prepared by chemical reduction with NaBH₄, resulting in nanoparticulate materials. Furthermore, in the case of the Pd₃Bi/C, a high degree of Pd–Bi alloy was achieved. When applied to glycerol electrochemical reforming, the electrochemical performance was enhanced so reducing the energy requirements for hydrogen production. Furthermore, in 24 h potentiostatic electrolysis, a smaller decay of the current was observed compared to the monometallic material, especially in the case of the Au₃Ag/C and Pd₃Bi/C electrocatalysts. Finally, the presence of the auxiliary metals altered the selectivity of the glycerol electro-oxidation. Bismuth added to Pt and Pd leads to an increase in the selectivity toward C₃ carboxylates, especially potassium tartronate in Pt–Bi materials operating at 30 °C. When the temperature is increased, this effect is counterbalanced by the larger amount of energy available, leading to a more heterogeneous product distribution in which oxalate and formate appear in higher percentages. Conversely, Ag leads to a more complex distribution product with large percentages of oxalate and formate.     

Carbon paper supported Pt/Au catalysts prepared via Cu underpotential deposition-redox replacement and investigation of their electrocatalytic activity for methanol oxidation and oxygen reduction reactions

Through a simple and rapid method, carbon papers (CPs) were coated with Au and the resulting Au/CP substrates were used for the preparation of Pt/Au/CP by Cu underpotential deposition (Cu UPD) and redox replacement technique. A series of Pt_n/Au/CP catalysts (where n = number of UPD-redox replacement cycles) were synthesized and their electrochemical properties for methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were investigated by electrochemical measurements. The Pt_n/Au/CP electrodes show higher electrocatalytic activity and enhanced poison tolerance for the MOR as compared to a commercial Pt/C on CP (Pt/C/CP). The highest mass specific activity and Pt utilization efficiency for MOR was observed on Pt₁/Au/CP with a thickness close to a monatomic Pt layer. Chronoamperometric tests in methanol solution revealed that Pt_n/Au/CPs have much higher CO tolerance compared to Pt/C/CP. Among the Pt_n/Au/CPs, CO tolerance decreases with increasing the amount of deposited Pt, indicating that the exposed Au atoms in close proximity to Pt plays a positive role against CO poisoning. Compared with the Pt/C/CP, all the Pt_n/Au/CP electrodes show more positive onset potentials and lower overpotentials for ORR. For instance, the onset potential of ORR is 150 mV more positive and the overpotential is ∼140 mV lower on Pt₄/Au/CP with respect to Pt/C/CP.     

High performance rare earth oxides LnOx (Ln = Sc,Y, La,Ce, Pr and Nd) modified Pt/C electrocatalysts for methanol electrooxidation

In this paper, the LnO_x (Ln = Sc, Y, La, Ce, Pr and Nd) modified Pt/C catalysts were prepared by wet precipitation and reduction method. The catalysts were characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). TEM showed that the Pt-PrO_x nanoparticles were uniformly dispersed on carbon with an average particle size of 5.0 nm in the Pt₃-(PrO_x)₁/C catalyst. EDX showed that Pt and Pr were successfully loaded on the carbon support without obvious loss. XRD showed that all the Pt/C and LnO_x modified Pt/C electrocatalysts (except for the Pt₃-(ScO_x)₁/C electrocatalyst) displayed the typical character of Pt face centered cubic (fcc) phase, whereas the Pt₃-(ScO_x)₁/C electrocatalyst contained the diffraction pattern of Pt face centered cubic and Sc₂O₃ phase. LnO_x modified Pt/C electrocatalysts were compared with Pt/C in terms of the electrochemical activity and stability for methanol electrooxidation using cyclic voltammetry (CV) and chronoamperometry (CA) in 0.5 M H₂SO₄ + 0.5 M CH₃OH solutions. The results showed that all the LnO_x (except for NdO_x) modified the Pt/C electrocatalysts gave higher catalytic activity and stability than Pt/C. In particular, the Pt₃-(PrO_x)₁/C eloctrocatalyst was found to be superior than others. Under this respect, several Pt-PrO_x/C catalysts with different atomic ratio of Pt/Pr were also identically prepared and characterized. It was found by CV and CA that the Pt₃-(PrO_x)₁/C and Pt₁-(PrO_x)₁/C catalysts showed better catalytic activity and stability than the Pt₅-(PrO_x)₁/C, Pt₁-(PrO_x)₃/C and Pt/C catalysts. The Pt₃-(PrO_x)₁/C and Pt₁-(PrO_x)₁/C catalysts had high catalytic activity and good stability, which could be used as novel electrocatalysts for direct methanol fuel cell.     

Electrochemical deposition of Au–Pt alloy particles with cauliflower-like microstructures for electrocatalytic methanol oxidation

Au–Pt alloy particles with cauliflower-like microstructures of varying Pt/Au ratios were electrodeposited on indium tin oxide (ITO) substrates by constant potential electrolysis at E = −0.25 V. The results of X-ray diffraction and X-ray photoelectron spectroscopy confirm that the bimetallic alloys can be obtained for different Pt/Au ratios including 4/1, 1/1 and 1/4. The formation of alloyed cauliflower-like microstructures may be the result of the fast formation of gold seeds as the core and subsequent simultaneous deposition of Au and Pt from cyclic voltammetric study. The effect of surface composition of Au–Pt alloy particles on electrocatalytic methanol oxidation were investigated in H₂SO₄ solution. The electrocatalytic abilities including electrochemical surface area, peak current density and the turnover number of methanol oxidation follow the order of Pt₄Au₁ > Pt > Pt₁Au₁. The results can be ascribed to that electronic effect may be prominent while bifunctional effect is insignificant for Au–Pt alloy systems because the electrocatalytic activity of Au is negligible in acidic media. Additionally, the Pt₄Au₁ electrode has superior kinetics of methanol electro-oxidation than monometallic Pt electrode by calculating the electron transfer coefficient (α).     

Improvement in the activity of Pt1Ni3/C by decorating with Au adatoms for ethylene glycol oxidation

The decoration of Pt₁Ni₃ nanoparticles supported on carbon black with Au adatoms and the electrocatalytic activity of the Au-decorated Pt₁Ni₃/C (Au/Pt₁Ni₃/C) for the oxidation of ethylene glycol (EG) in alkaline solution have been investigated. The decoration of Pt₁Ni₃/C with Au is performed by potentiostatically depositing a small amount of Au on Pt₁Ni₃/C, and the Au/Pt₁Ni₃/C catalysts with Au/Pt atomic ratios of ca. 0.02:1 and 0.08:1 are obtained. Physical and electrochemical characterizations reveal that a small part of the surface of Pt₁Ni₃ nanoparticles is covered by Au adatoms. In EG oxidation, the performances of Pt₁Ni₃/C before and after the Au decoration are quite different. Au/Pt₁Ni₃/C shows remarkably high peak intensity compared to Pt₁Ni₃/C, in spite of a decrease in the surface of Pt by Au adatoms. The low Pt content of Pt₁Ni₃ nanoparticles and the small Au loading also suggest advantages of the Au/Pt₁Ni₃/C catalysts in cost. The result of this study reveals a significant enhancing effect of Au adatoms on the activity of Pt₁Ni₃/C for EG oxidation.     

Carbon-supported PtAu alloy nanoparticle catalysts for enhanced electrocatalytic oxidation of formic acid

The understanding of the electrocatalytic activity of bimetallic nanoparticle catalysts requires the ability to precisely control the composition and phase properties. In this report, we describe a new strategy in the preparation of a series of carbon supported platinum-gold bimetallic nanoparticles with various bimetallic compositions which were loaded onto a carbon black support and subjected subsequently by thermal treatment (Pt_100−mAu_m/C). The Pt_100−mAu_m/C catalysts are characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), and induced coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for the bimetallic nanoparticles shows single-phase alloy character. This ability enabled us to establish the correlation between the bimetallic composition and the electrocatalytic activity for formic acid (FA) electrooxidation. The electrocatalytic activities of the catalysts toward FA oxidation reaction are shown to strongly depend on the bimetallic PtAu composition. Within a wide range of bimetallic composition, the Pt₅₀Au₅₀/C catalyst shows the highest electrocatalytic activity for the FA oxidation, with a mass activity eight times higher than that of Pt/C. The high performance of the PtAu/C catalyst can be ascribed to the increased selectivity toward the FA dehydrogenation at the decreased availability of adjacent Pt atoms.     

Ultra-low Au decorated PtNi alloy nanoparticles on carbon for high-efficiency electro-oxidation of methanol and formic acid

We provide a simple method to design and prepare a highly efficient Pt_10.9Au_0.2Ni_88.9/C trimetallic nanocatalyst with a novel nanostructure of ultra-low (0.075 wt%) Au decorated PtNi alloy nanoparticles for methanol oxidation (MOR) and formic acid oxidation (FAOR). The electro-catalytic properties of Pt_10.9Au_0.2Ni_88.9/C toward the MOR and FAOR are much more excellent than Pt_11.1Ni_88.9/C, Au_11.1Ni_88.9/C and commercial Pt/C, which is attributable to the synergy effect among Pt, Au, and Ni (electron charge donor effect of Au and Ni to Pt). It has transformed the surface electronic structure of Pt atoms. Moreover, Ni triggers the rearrange towards Pt and Au atoms, it could maximize the use of noble metals. The gold atoms decorated on the surface are conducive to the formation of OH_ads as well as to weaken the adsorption of CO_ads at platinum active sites. The Pt_10.9Au_0.2Ni_88.9/C catalyst also exhibits outstanding stability during the MOR and FAOR. A series of characterization techniques are adopted to reveal the nanostructures, electronic, and surficial active sites properties of Pt_10.9Au_0.2Ni_88.9/C.     

Pt-modified Au/C catalysts for direct glycerol electro-oxidation in an alkaline medium

Au-based catalysts promoted with Pt were prepared by using polyvinyl alcohol protection method. Different amounts of Pt (5, 10 and 15% of total metal) were added in the Au sol formation step to improve the activity of Au/C toward glycerol electro-oxidation in an alkaline medium. The physical and electrochemical properties of the as-prepared catalysts were explored. The average particle sizes of the Au/C and Pt-modified Au/C catalysts measured by transmission electron microscopy (TEM) were the same at around 4 nm. The PtAu/C alloy formation in the PtAu/C catalysts was confirmed by the increase of lattice parameter calculated from the X-ray diffraction (XRD) patterns and by the absence of Pt ring in the electron diffraction pattern. The change of binding energy in X-ray photoelectron spectroscopy (XPS) results indicated the interaction between Pt and Au. For glycerol electro-oxidation in an alkaline medium, the PtAu/C catalysts were more active than the Au/C catalyst as observed from an early onset potential and a shift of potential at maximum current density to a lower potential. Among the Pt-modified Au/C catalysts, the most active catalyst was Pt₁Au₉/C. The synergistic effects between Pt–Au was proven by a better performance of the PtAu/C compared to the physical mixed catalyst of Au/C and Pt/C at the same Pt:Au ratio. The Pt-modified Au/C catalysts were more stable than the Au/C, especially in a high potential region. This enhancement may be caused by the promotion effect of highly active PtO on the surface of the bimetallic catalyst.     

Electro-oxidation of ethylene glycol on PtCo metal synergy for direct ethylene glycol fuel cells: Reduced graphene oxide imparting a notable surface of action

Slow electro-oxidation reaction and low power output are two major limiting factors in successful commercialization of fuel cell technology. An efficient and stable electro-catalyst with effectual metal combination supported on a durable matrix may provide a viable solution to overcome these issues. The direct ethylene glycol fuel cell consisting of bimetallic anode catalysts are expected to lead out the high-power output issues. In the present paper, we emphasized on the synthesis of a high performing CO poisoning resistant Pt based binary anode catalysts for the electro-oxidation of ethylene glycol (EG) using a chemical reduction route. The electrocatalysts consists of PtCo alloy nanoparticles with different composition of Pt and Co, supported on reduced graphene oxide (rGO). Physical characterizations revealed the formation of bi-metallic catalysts within the size ranges from 2 nm to 3 nm. Electrochemical analysis revealed that Pt_xCo_y/rGO electrocatalyst with x: y molar ratio of 1:9 imparts the highest peak current and power density as compared to commercially available Pt/C and PtCo/C anode catalysts for ethylene glycol electro-oxidation. The power density (81.1 mW/cm²) obtained using Pt_xCo_y/rGO with x:y molar ratio of 1:9 metal catalyst in DEGFC is more than other synthesized catalysts at an operating temperature of 100 °C and the operating pressure of 1 bar with 2 M ethylene glycol as anode fuel and anode and cathode platinum metal loading of 2 mg/cm².     

Shape-tunable Pt–Ag nanocatalysts with excellent performance for oxygen reduction reaction

Shape-tunable PtAg nanocatalysts including PtAg nanoflowers (NFs) and PtAg nanowires (NWs) are prepared by a facile hydrothermal reduction method, via adjusting the precursor ratio of Pt/Ag and subsequent UV-irradiation. Physicochemical characterizations reveal that the as-prepared catalysts have a porous structure, which forms from the conversion of AgCl to Ag nanoparticles. These features favor both oxygen mass transfer and accessibility of active sites. The as-prepared Pt₁Ag₄ NWs exhibit superior catalytic performances for ORR. The mass activity of Pt₁Ag₄ NWs is 11.4 times higher than that of 20% Pt/C. More important, the electrochemically active surface area (ECSA) of Pt₁Ag₄ NWs is 2.5 times larger than that of commercial Pt/C.     

In-situ and ex-situ comparison of the electrochemical oxidation of SO2 on carbon supported Pt and Au catalysts

Electrochemical characterizations are performed using thin films and commercial carbon supported platinum and gold catalysts for sulfur dioxide oxidation, the primary electrochemical oxidation reaction in the Hybrid-sulfur (HyS) thermochemical process. Electrochemical evaluation of metal thin films qualitatively confirms the higher activity of Au over Pt, AuPt, Pd, and Ir for the electrochemical oxidation of SO₂. Ex-situ testing, using rotating disk electrode (RDE), shows an earlier onset potential for Au/C at low sulfuric acid concentrations (C ≤ 3.5 M) and a higher turnover frequency than Pt/C at sulfuric acid concentrations ranging from 3.5 M to 9 M. In-situ electrolysis experiments using low catalyst loadings (0.1 mg_Au cm⁻², a factor of ≥5 lower than typical loadings) confirm that Au nanoparticles exhibit higher current densities and greater stability than Pt nanoparticles. This is consistent with the thin film screening studies, which showed higher activity with increasing gold content in AuPt thin films. This work reveals an alternative material to state-of-the-art Pt to lower the energy needs and aid the HyS cycle in reaching the target of $2/kg H₂ set forth by the Department of Energy to achieve economic feasibility of large-scale hydrogen generation.     

Effects of stabilizers on the synthesis of Pt3Cox/C electrocatalysts for oxygen reduction

Pt₃Co_x/C electrocatalysts for use as cathodes in proton exchange membrane fuel cells are fabricated using various stabilizers to control the different reduction speeds between Pt and Co ions. Four different types of stabilizers—sodium acetate, oleylamine, tetraoctylammonium bromide (TOAB), and hexadecyltrimethylammonium bromide (CTAB)—differing in molecular structures and ionic states are tested. Primarily, Pt₃Co_x/C alloy nanoparticles are synthesized with 0.6 < x < 0.8 after heat treatment to remove the residual stabilizers. A significant improvement in the activity for oxygen reduction reaction is observed in the case of TOAB- and CTAB-mediated Pt₃Co_x/C catalysts. In particular, CTAB-mediated catalysts exhibit the best activity, which is about 2-times higher mass activity than commercial Pt/C catalyst. The higher mass activity is believed to result from not only the alloying effects with small atomic size Co but also better dispersion and smaller particle size after heat treatment at relatively low temperature.     

Surfactant-free room temperature synthesis of PdxPty/C assisted by ultra-sonication as highly active and stable catalysts for formic acid oxidation

Formic acid oxidation is usually catalyzed on PdPt bimetallic catalysts, which are synthesized by co-reduction of noble metal precursors in the presence of high molecular capping agents. In this work, surfactant-free Pd_xPt_y/C catalysts are synthesized by H₂ reduction in ethylene glycol assisted with ultrasonication vibration at room temperature. Nanoparticle agglomeration in the course of preparation has been sufficiently curbed by strong mechanical ultrasonication instead of traditionally-employed surfactants. As a result, “clean” surfactant-free Pd_xPt_y/C catalysts necessitate only simple washing before collection. The catalysts are characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The compositionally optimized Pd₁₀₀Pt₁/C catalyst registers a mass activity of 3171 A g⁻¹ (Pt + Pd) for formic acid oxidation in 0.5 M H₂SO₄+0.5 M HCOOH, which lists one of the best results reported so far and surpasses that of a commercial Pd/C by 5.6 times. Stability of the catalysts is investigated by cyclic voltammetric as well as chronoamperometric evaluations. This work offers a convenient and environmentally benign room-temperature route to synthesize highly active and stable catalysts for formic acid oxidation.     

Preparation and characterization of platinum/iron contained hydroxyapatite/carbon black composites

In this report, calcium ions in the porous hydroxyapatite (HAp) microspheres are partially exchanged with ferrous ions to form iron contained hydroxyapatite (FeHAp) on which Pt ions in H₂PtCl₆ solution are reduced to form Pt/FeHAp catalyst and finally mixed with carbon blacks to derive Pt/FeHAp/C catalysts. They exhibit the characteristics of Pt (1 1 0) facet with a sharp desorption peak at −0.109 V (vs. Ag/AgCl), the electrochemical surface area (ECSA) ranging from 73 to 224 m² g⁻¹ with little CO poisoning effect on Pt, and the mass activity ranging from 6.88 to 28.99 A g_Pt⁻¹ in methanol oxidation reaction (MOR) at 0.4 V (vs. Ag/AgCl). Besides, Pt/FeHAp reveals the lower onset potential in CO-stripping than Pt/C. These better performances of Pt/FeHAp/C catalysts, compared with Pt/C, are also related to the Pt (1 1 0) facet, the content of Fe, and the coexistence of Pt⁰ and Pt²⁺ in Pt/FeHAp.     

PtM/C (M = Sn,Ru, Pd,W) based anode direct ethanol–PEMFCs: Structural characteristics and cell performance

In the present work, the role of the structural characteristics of Pt-based catalysts on the single direct ethanol proton exchange membrane fuel cell (PEMFC) performance is examined. Several PtM/C (M = Sn, Ru, Pd, W) catalysts were characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) and then evaluated as anode catalysts in single direct ethanol fuel cells. XRD spectra showed that Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. According to the obtained experimental results, PtSn catalysts presented better electrocatalytic activity towards ethanol electro-oxidation. Based on these results, PtSn/C catalysts with different Pt/Sn atomic ratio were tested and compared. The maximum power density values obtained were correlated with the structural characteristics of the catalysts. A volcano type behaviour between the fuel cell maximum power density and the corresponding atomic percentage of Sn (Sn%) was observed. It was also observed that Sn% affects almost linearly the Pt_xSn_y catalysts’ lattice parameter.     

Understanding the electrocatalytic activity of PtxSny in direct ethanol fuel cells

In the present work, the activity of Pt_xSn_y/C catalysts towards ethanol, acetaldehyde and acetic acid electrooxidation reactions is investigated for each one separately by means of cyclic voltammetry. To this purpose, a series of Pt_xSn_y/C catalysts with different atomic ratio (x:y = 2:1, 3:2, 1:1) and small particle size (∼3 nm) are fast synthesized by using the pulse microwave assisted polyol method. The catalysts are well dispersed over the carbon support based on the physicochemical characterization by means of XRD and TEM. Concerning the ethanol electrooxidation, it is found that the Sn addition strongly enhances Pt's electrocatalytic activity and the contributing effect of Sn depends on: (i) the Sn content and (ii) the operating temperature. More precisely, at lower temperatures, Sn-rich catalysts exhibit better ethanol electrooxidation performance while at higher temperatures Sn-poor catalysts give better performance. In the case of acetaldehyde electrooxidation, Pt₁Sn₁/C catalyst exhibits the highest activity at all the investigated temperatures; due to the role of Sn, which could effectively remove C₂ species and inhibit the poison formation by supplying oxygen-containing species. Finally, it is found that the Pt_xSn_y/C catalysts are almost inactive (little current was measured) towards the acetic acid electrooxidation. The above findings indicate that Sn cannot substantially promote the electrooxidation of acetic acid to C₁ species.     

Enhanced photocatalytic hydrogen production over In-rich (Ag–In–Zn)S particles

The ratio of ZnS to AgInS₂ is usually adjusted to tune the band gaps of this quaternary (Ag–In–Zn)S semiconductor to increase photocatalytic activity. In this study, the [Zn]/[Ag] ratio was kept constant. The hydrogen production rate was enhanced by increasing the content of indium sulfide. Compared to the steady H₂ evolution rate obtained with equal moles of indium and silver ([In]/[Ag] = 1, 0.64 L/m² h), that obtained with In-rich photocatalyst ([In]/[Ag] = 2, 3.75 L/m² h) is over 5.86 times higher. The number of nanostep structures, on which the Pt cocatalysts were loaded by photodeposition, increased with the content of indium. The indium-rich samples did not induce phase separation between Ag_xIn_xZn_yS_2x+y and AgIn₅S₈, instead forming a single-phase solid solution. Although the photocatalytic activity decreased slightly for bare In-rich photocatalysts, Pt loading played a critical role in the hydrogen production rate. This study demonstrates the significant effect of In₂S₃ on this unique (Ag–In–Zn)S photocatalyst.     

Methanol electrooxidation on carbon supported Aucore–Ptshell nanoparticles synthesized by an epitaxial growth method

Au_core–Pt_shell (Au@Pt) nanoparticles supported on activated carbon (Au@Pt/C) are synthesized by an epitaxial growth method using HCOONa as a reducing agent. Through the characterization of the transmission electron microscope (TEM), high resolution TEM (HRTEM), high angle annular dark-field scanning TEM (HAADF-STEM) and X-ray powder diffraction (XRD), the Pt atoms grow epitaxially on the surface of the Au nanoparticles to form Pt shells with Au fcc structure. According to the results of the X-ray photoelectron spectroscopy (XPS), electrons transfer from Pt to Au. Cyclic voltammetry is employed to investigate the catalytic activities of the Au@Pt/C catalysts for the methanol electrooxidation (MEO) and the CO stripping. The results of the electrochemical measurements indicate that, the Au fcc structure of the Pt shell and the decrease in the electronic effect are propitious to the increases in the catalytic activity for the MEO and the CO tolerance of the Au@Pt/C catalysts.     

Rare-earth modified platinum-based electrocatalysts incorporating anodic glycerol oxidation reactions while promoting cathodic hydrogen evolution reactions

Glycerol electrooxidation (GOR) is a safe and clean method for conversion of glycerol. In the course of this work, a series of Pt_xCe/C catalysts have been synthesized by successive polyol reduction methods as well as etching and calcination. Various physicochemical characterrisation and electrochemical measurements have demonstrated the excellent performance of Pt₃Ce/C composites in glycerol oxidation (GOR) and hydrogen evolution reactions (HER). The Pt₃Ce/C catalyst showed better performance in GOR and HER compared to commercially available Pt/C electrocatalysts. This paper demonstrates an energy efficient electrocatalyst for the simultaneous precipitation of hydrogen from glycerol oxidation.