Preparation and characterisation of nanocrystalline IrxSn1−xO2 electrocatalytic powders

doi:10.1016/j.matchemphys.2005.04.039

Materials Chemistry and Physics

Volume 94, Issues 2–3, 15 December 2005, Pages 226-232

https://doi.org/10.1016/j.matchemphys.2005.04.039 Get rights and content

Abstract

Nanocrystalline oxide powders of the type Ir_xSn_1−xO₂ ( $0.2 \leq x \leq 1$ ) have been produced and characterised. These oxides have been developed primarily as oxygen evolution electrocatalysts for proton exchange membrane (PEM) water electrolysers. Two methods were used to produce the oxide materials: the modified polyol method and the Adams fusion method. X-ray diffraction analysis suggests that an iridium–tin oxide solid solution with a rutile structure can be produced using the modified polyol method, with a linear relationship between the lattice parameters and composition. The crystal size of the solid solution phase is below 15 nm for all compositions. The Adams fusion method results in at least two separate oxide phases, namely a tin rich oxide and an iridium rich oxide. X-ray photoelectron spectroscopy (XPS) analysis revealed no significant difference between the bulk and surface compositions, and that the iridium was present in at least two valent states. The electrical resistivity of the powders was compared, and an exponential increase in resistivity with tin addition was found. Overall the resistivity measurements suggest that the limit for tin addition is around 50–60 mol% due to the high ohmic losses expected at higher tin contents in a PEM water electrolyser.

Introduction

Proton exchange membrane (PEM) water electrolysers have been shown to be a promising method of producing carbon free hydrogen [1]. Recently, IrO₂based materials have been examined as the anode or oxygen evolution electrode at our group [2], [3], [4], [5], [6]. In this work the preparation and structural characterisation of Ir_xSn_1−xO₂( $0.2 \leq x \leq 1$ ) nanocrystalline powders is investigated. In particular, two methods for producing noble metal based oxides are compared based on X-ray diffraction (XRD) analysis and electrical conductivity measurements.

Noble metal oxides as electrocatalysts (particularly IrO₂ and RuO₂) are well established in many industrial electrochemical processes in the form of dimensionally stable anodes (DSA) as developed by Beer [7]. Most DSA electrodes are prepared by thermal decomposition of metal precursors onto titanium substates. This method is thought to be unsuitable for PEM water electrolysers due to the difficulty in obtaining good contact between the electrocatalytic layer and the membrane electrolyte. Therefore, to obtain an electrocatalytic layer on the membrane, either pre-prepared powders may be applied as an ink to the membrane [8], [9] or electrocatalytic particles can be synthesised directly on the surface or within the membrane [10], [11]. In our laboratory we normally use an ink-spray method, so have been concentrating on preparing noble metal based oxide powders.

Many methods are available for the synthesis of noble metal based oxides. The Adams fusion method [12] has been widely used to produce fine noble metal oxide powders [2], [3], [4], [5], [13], and is based on the oxidation of metal precursors in a molten nitrate melt. Sol-gel methods have also proved useful in producing noble metal based oxides [14], [15], [16], [17], [18], however precursor type can effect the properties of the material [18] as can the solvent removal stage [19]. Preparation of metal oxides by thermal or chemical oxidation of metallic colloids is an interesting concept as there exists a wide range of methods to synthesise such colloids [20], [21]. The polyol method is a relatively simple way to synthesise nanosized noble metal colloids such as iridium or ruthenium [22], [23], by the reduction of metal precursors in ethylene glycol. Our additional steps include the separation of the metallic colloids from the ethylene glycol by centrifugation, followed by thermal oxidation at elevated temperatures in air.

Previously it has been shown that SnO₂ improves the stability of IrO₂–RuO₂ anodes in PEM water electrolysers [13]. It has also been suggested that SnO₂does not reduce that activity of RuO₂ as much as TiO₂[24], [25]. For these reasons, additions of SnO₂to IrO₂ has been investigated.

Section snippets

Modified polyol method

Metal precursors (H₂IrCl_6⋅4H₂O¹ and SnCl_2⋅2H₂O² ) were added to ethylene glycol to achieve a total metal concentration of $1.67 \times 1 0^{- 2}$ mol l⁻¹. The glycol-precursor solution was then heated under a nitrogen atmosphere to the refluxing temperature and magnetically stirred for 2 h by which time a colloid had formed. The pH of this colloid–glycol mixture was then normally adjusted to pH 2.5 by the addition of 0.1 M NaOH solution and

Modified polyol method

On addition of the metal precursors to the ethylene glycol, the measured pH was seen to range from $- 0.15$ to 0.2, with the pH increasing linearly with increasing tin content. The colour of the solution was observed as the glycol mixture was heated (Table 1). Similar observations have been made during ruthenium synthesis by this method [27].

The colour changes are suggested to be due to the exchange or loss of ligands from the precursor complexes. After 2 h of refluxing, the measured pH was 0.83

Conclusions

The crystal properties of Ir_xSn_1−xO₂ powders, depend on the method used to prepare such materials. Adams fusion method results in an oxide consisting of at least two separate oxide phases, with one of these containing mostly SnO₂. The modified polyol method is believed to form a solid solution between iridium and tin oxide, with the lattice parameters increasing linearly with tin content. Addition of tin also causes the average crystal size to increase from around 3.5 to 15 nm. XPS clearly

Acknowledgements

The authors would like to acknowledge the financial support from the Norwegian Research Council and Norsk Hydro ASA.

References (38)

E. Rasten et al.
Electrochim. Acta
(2003)
H. Takenaka et al.
Int. J. Hydrogen Energy
(1982)
Y. Murakami et al.
Electrochim. Acta
(1994)
Y. Murakami et al.
Electrochim. Acta
(1994)
T. Lassali et al.
J. Non-Cryst. Solids
(2000)
F. Bonet et al.
NanoStruct. Mater.
(1999)
L. Kurihara et al.
NanoStruct. Mater.
(1995)
S. Trasatti
Electrochim. Acta
(1991)
A. Miyazaki et al.
Chem. Lett.
(1998)
S. Ardizzone et al.
Adv. Colloid Interface Sci.
(1996)

M. Rubel et al.

Vacuum

(1994)

F. Reames

Mater. Res. Bull.

(1976)

C. Mallika et al.

Thermochim. Acta

(2001)

L.J. Atanasoska et al.

Vacuum

(1990)

R. Oberlin, M. Fischer, Proceedings of the Sixth World Hydrogen Energy Conference on Hydrogen Energy Progress VI,...

E. Rasten, Electrocatalysis in Water Electrolysis with Solid Polymer Electrolyte, Ph.D. thesis, NTNU, Trondheim,...

E. Rasten, G. Hagen, R. Tunold, Proc. Energy and Electrochemical Processes for a Cleaner Environment 1991,...

A. Marshall et al.

J. New. Mat. Electrochem. Syst.

(2004)

Cited by (141)

Selection on antimony-doped tin oxide (ATO) as an efficient support for iridium-based oxygen evolution reaction (OER) catalyst in acidic media
2023, Materials Chemistry and Physics
Reducing the iridium content while preserving high OER activity is an important prerequisite for the progress of inexpensive anodic water splitting electrocatalysts in low pH medium. Here we report the effects of bulk and surface structures of antimony doped tin oxide (ATO) supports on the ATO supported Ir-based electrocatalyst's activity for oxygen evolution reaction (OER) in acidic media. Ability of the ATO supports to anchor the Ir nanoparticles, measured as the fraction of Ir species from reaction bath landed on ATO support (conversion efficiency; η_c), is found to be strongly dependent on its surface chemistry, characterized in terms of presence of surface oxygen groups (O_surface). Both O_surface content and electronic conductivity of ATOs show strong influence on OER activity. In general, high conductivity and low O_surface content are preferred for high OER activity, though low O_surface may compromise η_c. The optimal catalyst demonstrates superior OER activity of 777 A g⁻¹, 2.5 times that of the state-of-the-art commercial catalyst at 1.65 V vs. RHE. Further, the synthesized catalysts exhibit durability comparable to that of the commercial counterpart.
A novel Ir–Ru-based nanoparticle supported on ordered electrochemically synthesized TiO<inf>2</inf>-nanotube as a highly active and stable oxygen evolution reaction catalyst for water splitting in acidic media
2023, International Journal of Hydrogen Energy
Herein Iridium-Ruthenium-based OER electrocatalysts (Ir: Ru 60:40 at%) supported on electrochemically synthesized TiO₂ nanotubes (IrRuO_x/TNTs) at 80 wt% have been synthesized by the modified Adams fusion method. Physical and electrochemical characterization of the catalysts is compared with IrRuO_x, 80 wt% IrRuO_x/TiO₂ and commercial RuO₂. The total charge and the average diameter of the unsupported IrRuO_x are 1655.0 mC mg⁻¹ and 4.98 nm, respectively. The total charge and the average diameter for the IrRuO_x/TNT have been obtained at 3647.5 mC mg⁻¹ and 3.77 nm, respectively. IrRuO_x/TNT shows a current density of 1000 mA mg⁻¹ at 1.604 V_RHE and a Tafel slope of 68.9 mV dec⁻¹. Various methods, such as CV, CP, and CA, have been used to evaluate the stability of the catalysts. The results demonstrate that IrRuO_x/TNT is a stable catalyst for use in harsh acidic OER environments and can exhibit good activity in a low noble metal loading.
First-principles study of oxygen evolution on Co<inf>3</inf>O<inf>4</inf> with short-range ordered Ir doping
2023, Molecular Catalysis
Citation Excerpt :
However, because the extremely sluggish kinetics of oxygen evolution reaction (OER) at the anode, overall water splitting was hindered at a practical level [6]. Currently, IrO2 was the only known industrial OER electrocatalyst [7–10]. However, it was difficult to implement large-scale production and use of such catalysts because precious metals were inherently scarce and expensive (iridium US$60,670 kg−1) [11].
The large overpotential of oxygen evolution reaction (OER) in water-splitting process prevented its application in energy field, researchers attempted to find efficient catalysts. Here, we used short-range ordered Ir-doped Co₃O₄ (100) model to study the OER performance under various coordination conditions through first-principles calculations. This doping pattern enabled the model to display three types of active sites, included single Ir/Co site and double Ir sites, which were different in terms of propensity to adsorb reaction intermediates. The OER performance of three types of active sites with the same O and OH coverage was evaluated, we found that O covered surface increased OER catalytic activity for single Ir/Co site. While for double Ir sites, it exhibited the lowest overpotential among the above three types, and O/OH coverage had a little influence on its activity. Furthermore, Bader charge and partial density of states analyses showed that, for single Ir/Co site, the overpotential on covered surface was reduced due to the valence electrons decrease at the metal site. While for double Ir sites, the overpotential reduction was due to the unique adsorption patterns. Additionally, the solvation effect was considered. It was found that the solvation had a key effect on the adsorption energy depending on the binding site of the intermediate. But the overpotential trend in solvent was similar with that in vacuum on the same active site.
Fully anhydrous HCl electrolysis using polybenzimidazole membranes
2022, International Journal of Hydrogen Energy
We demonstrate for the first time a fully anhydrous gas-phase hydrogen chloride electrolyzer. By taking advantage of polybenzimidazole's (PBI) low membrane resistivity in anhydrous conditions (0.87 ± 0.57 Ω-cm² at 160 °C) and its temperature and acid environment stability, we are able to directly convert pure hydrogen chloride gas to dry hydrogen and dry chlorine at efficiencies nearing 100% at an electrolyzer temperature of 160 °C and electrolyzer potential of 1.8 V. Finally, we discuss steps to further improve this electrolysis process in terms of both electrolyzer performance and cost reduction.
Experimental and first-principles investigations on W-Ir mixed matrices cathodes with improved emission performance
2022, Applied Surface Science
Fundamental understanding of the intrinsic emission mechanism of mixed W matrix Ba type dispenser cathode is critical to rational design of advanced device with highly desired performance. In this work, experimental and theoretical work was conducted to investigate the underlying effect of Ir metal on the improved emission properties of mixed W cathodes. The results indicated that introduced Ir improves the stability of Ba-O dipole on the cathode surface by alloying with W rather than reaction with impregnants, which leads to higher atomic ratio of Ba/O on the surface emission layer with 50 wt% Ir adding, and therefore accounts for the enhanced emission current density of 11.90 A/cm² with 2.2 times higher than W matrix dispenser cathode at 1000 ℃_b. Furthermore, first-principles calculation was used to investigate the adsorption energy, work function, Bader charges, dipole moment and d-band center based on the high stable configuration of Ba_0.25O_0.5 adsorbing on IrW (1 1 1) and W (1 1 0), which explains the lowed work function of Ir-W cathode and in turn improved the emission property.
Photodeposited IrO<inf>2</inf> on TiO<inf>2</inf> support as a catalyst for oxygen evolution reaction
2021, Journal of Electroanalytical Chemistry
Citation Excerpt :
Nevertheless, nowadays IrO2 is used as a typical anode electrocatalyst for water electrolysis. The most common methods reported in the literature for the synthesis of nanosized IrO2 catalysts are the Adams fusion method [10–13], sol–gel methods [14–16], a modified polyol method [17,18], hydrolysis [19], while those of subsequent electrode preparation include spray deposition [20], thermal decomposition [21,22] and sputtering [23]. Using appropriate catalyst supports could improve catalyst utilization [24] and the stability of catalyst layers with reduced loading of the precious Ir metal [25].
A simple, alternative, catalyst preparation method was proposed in order to combine the properties of photoactive and stable TiO₂ with state-of-the art of IrO₂ for the oxygen evolution reaction (OER). IrO₂ nanoparticles were obtained in the process of photodeposition on the surface of TiO₂ powder by UV illumination from appropriate Ir salt aqueous solution. Physicochemical characterization of the resulting IrO₂/TiO₂ composite, containing 25% w/w Ir, was carried out by transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the prepared IrO₂/TiO₂ catalyst was compared with that of commercial unsupported IrO₂. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to identify the surface electrochemistry and OER of the IrO₂/TiO₂ catalyst. Electrochemical impedance spectroscopy (EIS) was used to determine uncompensated and charge transfer resistance. CA experiments were carried out in order to evaluate the stability of the IrO₂/TiO₂ composite during OER in the dark and under UV light irradiation. The photodeposition method on a TiO₂ support resulted in 1–2 nm Ir nanoparticles, very well dispersed on the surface and in their oxidized state (IrO₂). Electrochemical results indicated that despite its lower conductivity, the IrO₂/TiO₂ composite exhibits comparable intrinsic electrocatalytic activity for OER with that of the commercial IrO₂ catalyst. It was found that under UV light irradiation there has been improvement of the stability of the IrO₂/TiO₂ performance during oxygen evolution (presumably due to sustained activation of reactive species via photogenerated holes or OH radicals) as well as current enhancement (due to the interaction between the photogenerated holes in TiO₂ support and IrO₂ nanoparticles). These would be beneficial effects in prolonged water photo-electrolysis.

View all citing articles on Scopus

^✠: Deceased.

View full text

Preparation and characterisation of nanocrystalline IrxSn1−xO2 electrocatalytic powders

Abstract

Introduction

Section snippets

Modified polyol method

Modified polyol method

Conclusions

Acknowledgements

Electrochim. Acta

Int. J. Hydrogen Energy

Electrochim. Acta

Electrochim. Acta

J. Non-Cryst. Solids

NanoStruct. Mater.

NanoStruct. Mater.

Electrochim. Acta

Chem. Lett.

Adv. Colloid Interface Sci.

Vacuum

Mater. Res. Bull.

Thermochim. Acta

Vacuum

J. New. Mat. Electrochem. Syst.

Preparation and characterisation of nanocrystalline Ir_xSn_1−xO₂ electrocatalytic powders