Electrochemical corrosion of platinum electrode in concentrated sulfuric acid

We report on the electrochemical corrosion of a Pt electrode in strong sulfuric acid. The electrochemical measurements were conducted using a Pt-flag working electrode, Ag/Ag₂SO₄ reference electrode and Pt counter electrode at 25 °C. The measured cyclic voltammograms significantly changed in the H₂SO₄ concentration range of 0.5–18 mol dm⁻³, especially from 14 to 18 mol dm⁻³. After successive potential sweeps for 15 h in 16 mol dm⁻³ H₂SO₄, a weight loss of the Pt-flag electrode was realized. In contrast, a controlled potential electrolysis by cathodic polarization caused a weight gain, which was attributed to sulfur deposition by the H₂SO₄ reduction. The subsequent anodic polarization produced corrosion of the deposited sulfur. Consequently, the alternating polarization generated platinum corrosion, resulted in the production of platinum and sulfur composite particulates in the solution.     

Study of Pt electrode dissolution in H2O2-containing H2SO4 solution using an electrochemical quartz crystal microbalance

Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H₂O₂-containing 0.5 mol dm⁻³ H₂SO₄. The Pt electrode weight-loss of ca. 0.4 μg cm⁻² is observed during nine potential sweeps between 0.01 and 1.36 V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H₂O₂ (<0.05 μg cm⁻²). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H₂O₂ concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H₂O₂ accelerates the Pt dissolution. Based on these results, H₂O₂ is known to be a major factor contributing to the Pt dissolution.     

Ultra low Pt-loading electrode prepared by displacement of electrodeposited Cu particles on a porous carbon electrode

Ultra low Pt-loading and high Pt utilization electrodes were prepared by displacement of electrodeposited Cu on a porous carbon electrode. Copper particles were electrodeposited on a porous carbon electrode (PCE) by four-step deposition (FSD) at first. The size and dispersion of deposited Cu particles were markedly improved with application of the FSD. The Cu deposits were then displaced by platinum as dipping a Cu/PCE in a platinum salt solution. Sequentially, Pt particles supported on the PCE were obtained. The Pt/PCE electrode prepared via the FSD of Cu overcomes the problem of the hydrogen evolution reaction accompanied with direct platinum electrochemical deposition, and has a high Pt dispersion. The single cell consisting of the electrodes Pt/PCE via the FSD of Cu outputs a power of 0.45 W cm⁻² with ultra low Pt loadings of 0.196 mg cm⁻² MEA (0.098 mg cm⁻² per each side of the MEA) at no backpressure of reactant gases.     

Fabrication of bimetallic Cu/Pt nanoparticles modified glassy carbon electrode and its catalytic activity toward hydrogen evolution reaction

The film of poly(8-hydroxyquinoline) was formed by cyclic voltammetery method on the surface of glassy carbon electrode and poly(8-hydroxyquinoline) modified glassy carbon electrode, p(8-HQ)MGCE, was prepared. Cu²⁺ ion was adsorbed on the polymer matrix due to complexation with 8-hydroxyquinoline units Copper nanoparticles were deposited onto p(8-HQ)MGCE by applying potential and prepared copper nanoparticles galvanic replaced with platinum to fabricate poly(8-hydroxyquinoline)–Pt/Cu composite on the surface of GCE. Stripping voltammetery of Cu in aqueous 0.1 M KSCN + Britton–Robinson buffer, pH = 2.0, solution was used to quantify the copper present on the electrode surface. The amount of platinum was estimated from the electrooxidation peak of Pt in aqueous 0.1 M H₂SO₄ solution. The nature of Cu/Pt–p(8-HQ) on the surface of GCE was characterized by scanning electron microscopy. Cu/Pt–p(8-HQ) modified GCE can be used as a convenient conducting substrate for electrocatalytic hydrogen evolution reaction (HER). The effects of different parameters such as number of cycles, replacement time, scan rate of potential, and etc were investigated to obtaining optimum condition for HER.     

Hydrogen production by steam reforming of acetic acid: Comparison of conventional supported metal catalysts and metal-incorporated mesoporous smectite-like catalysts

The activities of various metal catalysts were tested in steam reforming of acetic acid for the production of H₂, using conventional metal oxides and transition metal-incorporated mesoporous smectite-like materials as supports. It has been found that Pt is superior to Ni, Co, and Fe among Al₂O₃ supported catalysts, Al₂O₃ is more effective than ZrO₂ and SiO₂ as support for Pt, Ni incorporated smectite (SM(Ni)) support is more effective than Fe and Co incorporated ones for Pt, and SM(Ni) is also active in the absence of Pt. The total activity for the conversion of acetic acid is in the order of Pt/Al₂O₃ > Pt/SM(Ni) > SM(Ni) but the ability of H₂ production is comparable among these catalysts. These catalysts (and the other ones) were observed to lose their activities during the reforming reactions. The activity of Pt/Al₂O₃ decreased during the whole course of reaction up to 10 h. In contrast, the activity of SM(Ni) also decreased within 2 h but it showed a stable activity in the following stage of reaction. The initial activity of the used Pt/SM(Ni) and SM(Ni) was able to be almost completely restored by thermal treatment with H₂ but less effectively for the used Pt/Al₂O₃. The catalyst deactivation was shown to occur by the formation and deposition of carbon materials on the catalysts (XRD, TEM, thermal analysis). The properties of carbon deposits formed on Pt/Al₂O₃ and SM(Ni) catalysts should be different and this may be responsible for the differences in the extent of deactivation and in the regeneration behavior between the two catalysts.     

Impact of ultra-low Pt loadings on the performance of anode/cathode in a proton-exchange membrane fuel cell

This study focuses on the elaboration of PEMFC electrodes containing ultra-low platinum (Pt) loadings by direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD). DLI-MOCVD offers a large number of advantages for the elaboration of model PEMFC electrodes. First, by using different metal precursors or elaboration temperature, the size of the Pt nanoparticles and thus the intrinsic catalytic activity can easily be tailored in the nanometer range. In this work, Pt nanoparticles (1-5 nm) with remarkable low degree of agglomeration and uniform distribution were deposited onto the microporous side of a commercial gas-diffusion layer (GDL). Second, reduction of the Pt loading is made possible by varying the Pt deposition time and its influence of the cell performance can be extracted without variation of the thickness of the catalytic layer (in previous studies, a decrease of the catalyst utilization was observed when increasing the Pt loading, i.e. the thickness of the catalytic layer (CL)). The electrocatalytic activity of home-made Pt nanoparticles elaborated by DLI-MOCVD was measured in liquid electrolyte or in complete fuel cell operating on H₂/O₂ or H₂/air and compared vs. that of a commercially available electrode containing 500 μg_Pt cm⁻² (Pt_Ref500). At the cathode, the performance of the electrodes containing 104-226 μg of Pt per cm² of electrode compares favorably with that of the Pt_Ref500 in H₂/O₂ conditions. In H₂/air conditions, additional mass-transport losses are detected in the low-current density region but the high effectiveness of our electrodes improves the performance in the high-current density region. At the anode, the Pt loading can be reduced to 35 μg_Pt cm⁻² without any voltage loss in agreement with previous observations.     

A preliminary study of a novel catalyst Al2O3·Na2O·xH2O/NaOH/Al(OH)3 for production of hydrogen and hydrogen-rich gas by steam gasification from cellulose

The new catalyst, Al₂O₃·Na₂O·xH₂O/NaOH/Al(OH)₃, was made by means of hydrolyzation and hydration of sodium aluminum oxide (Al₂O₃·Na₂O). Hydrogen and hydrogen-rich gas were produced through the reaction of cellulose with the catalyst and steam. In order to avoid production of tar, the gasification temperature is controlled at ≤673 K. The temperature of producing hydrogen is controlled at about 473–623 K. The conversion degree of hydrogen from cellulose at about 473–673 K could come up to 59.63%. The production of hydrogen-rich gas was set at about 673 K. The gasification residue could be used as material for combustion. Al₂O₃·Na₂O could be regenerated from the byproducts Al₂O₃ and Na₂CO₃ produced in the combustion process. The catalyst could be re-prepared from the regenerative Al₂O₃·Na₂O.     

Sulfuric acid decomposition on Pt/SiC-coated-alumina catalysts for SI cycle hydrogen production

Sulfuric acid decomposition was conducted at atmospheric pressure and a GHSV of 72,000 mL/g_cat h in the temperature ranges from 650 to 850 °C. The Pt–Al (1wt% Pt/Al₂O₃) and and Pt–SiC–Al (1wt% Pt/SiC-coated-Al₂O₃) catalysts were prepared by an impregnation method. The Pt–Al catalyst rapidly deactivated at 650 and 700 °C, but was stable at 750 and 850 °C. The aluminum sulfate was observed on the spent Pt–Al catalyst by an FT-IR, an X-ray spectroscopy and a TGA/DSC analyzer, which was suggested to be a cause of the deactivation at lower reaction temperature. The alumina support was coated with SiC by a CVD method with methyltrichlorosilane (MTS) to get a non-corrosive support (SiC–Al) with high surface areas. The thermal analysis of the spent Pt–SiC–Al showed that the aluminum sulfate formation was suppressed during the sulfuric acid decomposition. The Pt–SiC–Al catalyst was not only active higher than the Pt–Al catalyst, but was also stable at all the tested reaction temperature.     

Synthesis and characterization of platinum nanoparticles on in situ grown carbon nanotubes based carbon paper for proton exchange membrane fuel cell cathode

Multi-walled carbon nanotubes (MWCNTs) based micro-porous layer on the carbon paper substrates was prepared by in situ growth in a chemical vapor deposition setup. Platinum nanoparticles were deposited on in situ grown MWCNTs/carbon paper by a wet chemistry route at <100 °C. The in situ MWCNTs/carbon paper was initially surface modified by silane derivative to incorporate sulfonic acid–silicate intermediate groups which act as anchors for metal ions. Platinum nanoparticles deposition on the in situ MWCNTs/carbon paper was carried out by reducing platinum (II) acetylacetonate precursor using glacial acetic acid. High resolution TEM images showed that the platinum particles are homogeneously distributed on the outer surface of MWCNTs with a size range of 1–2 nm. The Pt/MWCNTs/carbon paper electrode with a loading of 0.3 and 0.5 mg Pt cm⁻² was evaluated in proton exchange membrane single cell fuel cell using H₂/O₂. The single cells exhibited a peak power density of 600 and 800 mW cm⁻² with catalyst loadings of 0.3 and 0.5 mg Pt cm⁻², respectively with H₂/O₂ at 80 °C, using Nafion-212 electrolyte. In order to understand the intrinsically higher fuel cell performance, the electrochemically active surface area was estimated by the cyclic voltammetry of the Pt/MWCNTs/carbon paper.     

Electrodeposition preparation of Pt–HxWO3 composite and its catalytic activity toward oxygen reduction reaction

Platinum–hydrogen tungsten bronze (Pt–H_xWO₃) was prepared on glass carbon electrode by potentiostat in 0.1 mM H₂PtCl₆ + 4 mM Na₂WO₄ + 2 M H₂SO₄. Its surface morphology, structure and activity toward oxygen reduction reaction were studied with scan electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and linear sweeping voltammetry. It is found that platinum and hydrogen tungsten bronze can be co-deposited together on glassy carbon and the activity of platinum toward oxygen reduction can be improved significantly by H_xWO₃. Furthermore, the activity of Pt–H_xWO₃ toward oxygen reduction is hardly influenced by methanol.     

Fabrication of platinum coated nanoporous gold film electrode: A nanostructured ultra low-platinum loading electrocatalyst for hydrogen evolution reaction

The electrolytic hydrogen evolution reaction (HER) on platinum coated nanoporous gold film (PtNPGF) electrode is demonstrated. The deposition of platinum occurred as a spontaneous redox process in which a copper layer, obtained by underpotential deposition, was oxidized by platinum ions, which were reduced and simultaneously deposited. The present method could provide a very low Pt-loading electrode and the results demonstrated that ultra thin Pt coating effected efficiently and behaved as the nanostructured Pt for electrocatalytic hydrogen evolution reaction. The loading of Pt was calculated as 4.2 × 10⁻³ μg cm⁻² for PtNPGF electrode. The current density at −0.4 V and −0.8 V vs. Ag/AgCl was as high as 0.66 A μg⁻¹ Pt and 3 A μg⁻¹ Pt, respectively and the j₀ was evaluated as 0.03 mA cm⁻² or 8 mA μg⁻¹ Pt. The results indicated that increasing electrode area had no catalytic effect, but the nanostructure nature of as-fabricated electrode and submonolayer deposition of copper resulted in electrocatalytic activity for PtNPGF electrode.     

Photocatalytic water splitting with In-doped H2LaNb2O7 composite oxide semiconductors

The In-doped HLaNb₂O₇ oxide semiconductors synthesized by solid-state reaction followed by an ion-exchange reaction were found to be a novel composite photocatalyst system with enhanced activity for water splitting. Pt was incorporated in the interlayer of In-doped HLaNb₂O₇ by the stepwise intercalation reaction. The In-doped HLaNb₂O₇ powder samples were characterized with X-ray diffraction (XRD) and UV-vis diffuse reflectance spectrometry. The photocatalytic activities of Pt-loaded In-doped HLaNb₂O₇ and individual precursor materials were evaluated by H₂ evolution from aqueous CH₃OH solution under UV light irradiation. It was found that the composite In-doped HLaNb₂O₇ showed a higher H₂ evolution rate in comparison with individual materials. The hydrogen production activity of In-doped HLaNb₂O₇ was greatly enhanced by Pt co-incorporation. The In content in the In-doped HLaNb₂O₇ system was discussed in relation to the photophysical and photocatalytic properties. As In content equal 5 mol%, the HLaNb₂O₇:In/Pt showed a photocatalytic activity of 354 cm³ g⁻¹ hydrogen evolution in 10 vol% methanol solution under irradiation from a 100 W mercury lamp at 333 K for 3 h.     

Hydrogen production from 2-propanol over Pt/Al2O3 and Ru/Al2O3 catalysts in supercritical water

One of the alternative energy sources to fossil fuels is the use of hydrogen as an energy carrier, which provides zero emission of pollutants and high-energy efficiency when used in fuel cells, hydrogen internal combustion engines (HICE) or hydrogen-blend gaseous fueled internal combustion engines (HBICE). The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, with very short reaction times. In this study, hydrogen production from 2-propanol over Pt/Al₂O₃ and Ru/Al₂O₃ catalysts was investigated in supercritical water. To investigate the influences on hydrogen production, the experiments were carried out in the temperature range of 400–550 °C and in the reaction time range of 10–30 s, under a pressure of 25 MPa. In addition, different 2-propanol concentrations and reaction pressures were tested in order to comprehend the effects on the gasification yield and hydrogen production. It was found that Pt/Al₂O₃ catalyst was much more selective and effective for hydrogen production when compared to Ru/Al₂O₃. During the catalytic gasification of a 0.5 M solution of 2-propanol, a hydrogen content up to 96 mol% for a gasification yield of 5 L/L feed was obtained.     

Electrocatalytic properties of Ti/Pt–IrO2 anode for oxygen evolution in PEM water electrolysis

A novel Pt–IrO₂ electrocatalyst was prepared using the dip-coating/calcinations method on titanium substrates. Titanium electrodes coated with oxides were investigated for oxygen evolution. Experimental results showed that Ti/Pt–IrO₂ electrode containing 30 mol% Pt in the coating exhibited significantly higher electrocatalytic activity for oxygen evolution compared to Ti/IrO₂ prepared by the same method, which is also supported by the electrochemical impedance data. Stability tests demonstrated Pt–IrO₂ electrocatalyst had a service cycle of 10,000 times in 0.1 M H₂SO₄ solution. And the anode surface had hardly discovered cracks and had compact structures, which contributed to stable nature of the electrode together with good conductivity and specific interaction between Pt and IrO₂ formed during the calcination. Furthermore, the enhanced catalytic activity for O₂ evolution at Ti/Pt–IrO₂ electrode is preliminarily discussed using the Mott–Schottky analysis.     

Hydrogen permeation on Al2O3-based nickel/cobalt composite membranes

Al₂O₃ was synthesized using the sol-gel process with aluminum isopropoxide as the precursor and primary distilled water as the solvent. Nickel and cobalt metal powders were used to increase the strength of the membranes. The Al₂O₃-based membranes were prepared using HPS following a mechanical alloying process. The phase transformation, thermal evolution, surface and cross-section morphology of Al₂O₃ and Al₂O₃-based membranes were characterized by XRD, TG-DTA and FE-SEM. The hydrogen permeation of Al₂O₃-based membranes was examined at 300–473 K under increasing pressure. Hydrogen permeation flux through an Al₂O₃-20wt%Co membrane was obtained to 2.36 mol m⁻² s⁻¹. Reaction enthalpy was calculated to 4.5 kJ/mol using a Van’t Hoff’s plot.     

New nano-structured and interactive supported composite electrocatalysts for hydrogen evolution with partially replaced platinum loading

This work is concerned with preparation and characterization of nano-structured composite electrocatalytic material for hydrogen evolution based on CoPt hyper d-metallic phase and anatase (TiO₂) hypo d-phase, both deposited on multiwalled carbon nanotubes (MWCNTs) as a carbon substrate. The main goal is partially or completely to replace Pt as the electrocatalytic material. Four electrocatalytic systems were prepared with common composition 10% Me + 18% TiO₂ + MWCNTs, where Me = Co, CoPt (4:1, wt. ratio), CoPt (1:1, wt. ratio) and Pt. The structural changes and their influence on electrocatalytic activity were studied by means of XRD, TEM, SEM and FTIR. The electrocatalytic activity was assessed in aqueous alkaline and polymer acidic electrolytes by means of steady-state galvanostatic method. It was found that Co strongly affects the platinum particle size. The addition of Co reduces platinum particle's size from 11 nm (in pure Pt metallic system) to 4 nm (in both systems 4:1 and 1:1), i.e. almost by 3 times. The corresponding increase of the surface area and the number of the active catalytic centres improves the efficiency, despite the fact that the amount of used platinum was decreased up to 5 times. The catalyst based on CoPt (1:1) performed the best, while the activity of the pure platinum and CoPt (4:1) systems were very close. Generally, the studied electrocatalysts have shown good and stable performances for hydrogen evolution in PEM electrochemical cell. The influence of the hydrogen electrodes under investigation on the water electrolysis efficiency at current density of 0.3 A cm⁻² was assessed, using previous data oxygen evolution on IrO_x electrode. Related to the performances of commercial Pt (ELAT) electrode, when hydrogen electrodes with the prepared mixed electrocatalysts were used, the water electrolysis efficiency was only 5% lower for CoPt (1:1), nearly 10% lower for CoPt (4:1) and 13% lower in the case of pure Co-based electrocatalyst.     

Photocurrent and photoelectrochemical hydrogen production with tin porphyrin and platinum nanowires immobilized with nafion on glassy carbon electrode

Platinum nanowires mixed with Tin meso-tetra (4-pyridyl) porphine dichloride and nafion solution was used to modify the surface of glassy carbon electrode for photocurrent generation and photo-electrochemical hydrogen production. Different concentrations of porphyrin (50 μM, 100 μM, 300 μM and 500 μM) and platinum loading (200 μg/cm², 400 μg/cm², 600 μg/cm² and 800 μg/cm²) were tested at −150 mV Vs Ag/AgCl in reaction cell containing the modified glassy carbon electrode as working electrode, platinum wire as counter electrode and Ag/AgCl as reference electrode, under illumination to determine the optimum, based on photocurrent production in 50 mM potassium hydrogen phthalate buffer (pH 3) containing 0.1Na₂SO₄ as supporting electrolyte. Optimum photocurrent was obtained at 100 μM tin porphyrin and 600 μg/cm² platinum loading. Detectable amount of hydrogen was produced at −350 mV Vs Ag/AgCl under irradiation with visible light.     

CuO nanosheets grown on cupper foil as the catalyst for H2O2 electroreduction in alkaline medium

The growth of CuO nanosheet arrays on Cu foil was demonstrated. The morphology and structure of the CuO were examined by scanning electron microscopy and X-ray diffraction spectroscopy. The catalytic performance of the obtained CuO/Cu electrode for hydrogen peroxide electroreduction in 3.0 mol dm⁻³ KOH was evaluated by means of cyclic voltammetry and chronoamperometry. The CuO/Cu electrode shows an onset potential for H₂O₂ electroreduction comparable to Co₃O₄ nanowire arrays grown on Ni foam and around 100 mV more negative than precious metal catalysts, such as Pt and Pd, demonstrating its good catalytic activity for H₂O₂ electroreduction. The stabilized mass current density for H₂O₂ electroreduction on the CuO/Cu electrode at −0.3 V reached about 57% of that on Co₃O₄ nanowire arrays grown on nickel foam. Compared to conventional fuel cell electrodes fabricated by mixing active materials with conducting agents and polymer binders, this electrode of CuO nanosheet arrays directly grown on Cu has superior mass transport property, which combining with its low-cost and facile preparation, make it a promising electrode for fuel cell using H₂O₂ as the oxidant.     

Corrosion inhibition of mild steel in acidic media using newly synthesized heterocyclic organic molecules

Hydrogen evolution reaction (HER) (cathodic reaction) of mild steel immersed in H₂SO₄ acid was investigated. Electrochemical corrosion behavior and hydrogen evolution reaction of mild steel has been investigated using different electrochemical techniques. Steel was polarized vs. saturated calomel electrode (SCE) in naturally aerated 1.0 M H₂SO₄ aqueous solution containing four organic inhibitors (newly synthesized heterocyclic compounds) of different concentrations. The observed different influence of corrosion inhibitors on the hydrogen evolution reaction was associated with the different chemical composition and structure. Polarization results showed that corrosion current density, i_corr, and hydrogen evolution decreases with increasing concentration of inhibitors in 1.0 M H₂SO₄, indicating a decrease in the corrosion rate. Electrochemical impedance spectroscopy (EIS) measurements confirmed this behavior. An increase of temperature leads to increase in the corrosion or hydrogen evolution rate and a decrease of the total resistance value, R_T. The obtained results were confirmed by surface examination.     

Selective CO oxidation with real methanol reformate over monolithic Pt group catalysts: PEMFC applications

Alumina supported Pt group metal monolithic catalysts were investigated for selective oxidation of CO in hydrogen-rich methanol reforming gas for proton exchange membrane fuel cell (PEMFC) applications. The results are described and discussed in the present paper and show that Pt/γ_Al2O3$\mathrm{Pt}/\gamma {\mathrm{Al}}_2{\mathrm{O}}_3$ was the most promising candidate to selectively oxidize CO from an amount of about 1 vol% to less than 100 ppm. We have investigated the effect of the O₂ to CO feed ratio, the feed concentration of CO, the presence of H₂O and/or CO₂, and the space velocity on the activity, selectivity and stability of Pt/Al₂O₃ monolithic catalysts. Afterwards, the Pt/Al₂O₃ catalyst was scaled up and applied in 5 kW hydrogen producing systems based on methanol steam reforming and autothermal reforming. The hydrogen produced was then used as fuel for an integrated PEMFC.