Electrocatalysis Complete solutions for electrocatalysis and forced convection measurements 02 Electrocatalysis and forced convection Electrocatalysis is the catalysis of an electrode reaction. and kinetics of the electrode reaction. Forced convection The electrocatalytic effect leads to an increase of the methods offer the advantage of reducing the contribu-standard rate constant of the electrode reaction, result-tions from mass-transport and providing a direct access ing in a higher current density, or to a decrease in over-to kinetic and mechanistic information. Metrohm Autolab potential when other rate limiting steps are involved. The provides a complete range of products for these demand-study of an electrocatalytic process requires insights in ing experiments. the influence of electrode properties on the mechanism Oxygen reduction reaction (ORR) – an essential electrochemical reaction The oxygen reduction reaction (ORR) is the most impor-Current research focuses on platinum, the best catalyst 03 tant reaction in life processes such as biological respira-for ORR, or combinations of this metal with other materi-tion, in corrosion and in energy converting systems such als, as well as on the use of non-noble metal catalysts. as fuel cells. ORR in aqueous solutions occurs mainly by two pathways: the direct 4-electron reduction pathway Forced convection has been the method of choice for from O to H O, and the 2-electron reduction pathway study ing this and other reactions. Rotating disk and ro - 2 2 from O to hydrogen peroxide (H O ). In non-aqueous tat ing ring-disk measurement provide valuable insights in 2 2 2 aprotic solvents and/or in alkaline solutions, the 1-elec-the kinetics and mechanism involved in the reaction. tron reduction pathway from O to superoxide (O -) can 2 2 also occur. The experimental characterization of these electrocata-lysts requires the cleanest possible conditions as impuri-ORR is known to suffer from very sluggish kinetics and ties may lead to incorrect data and conclusions. large overpotentials are required to achieve a decent turn over rate on the electrode. For energy convertion Find out how you can perform these experiments with pro cesses, these kinetics need to be improved to reach a the dedicated Metrohm Autolab products. practical usable level in fuel cells. ECAT-compact – basic package for electrocatalysis experiments The compact PGSTAT204, fitted with the dual-04 mode BA bipotentiostat module provides a convenient solution for electrochemical measurements using forced convection. The rotating ring-disk electrode (RRDE) can be remotely controlled by the instrument and the BA module offers the possibility to perform both collection-detection ex pe-ri ments and shielding experiments. • Small but powerful Despite its small footprint, the PGSTAT204 pro vides all the functionality required for high quality and accurate electrochemical measurements. • Dual mode bipotentiostat The BA module can be used to control the second working electrode in both bipotentiostat mode or scanning bipotentiostat mode. • Accurate motor controller High precision control of the rotation rate, from 100 to 10 000 RPM. • Built-in analog integrator 05 For charge and cyclic voltammetry current in tegration measurements. • Electrochemical cell Dedicated electrochemical cell for electrocatalysis measurements. • Waterbath control Software interface to external waterbath for temperature regulation • Generation collection or shielding The rotating ring-disk electrode can be used for both generation collection or shielding ex periments. • Monitor cable Provides connections for analog signals and control for the Autolab motor controller. • Powerful software Advanced electrochemical NOVA 2 control software with built-in Levich and Koutecký- Levich analysis methods. ECAT-complete – complete package for electrocatalysis experiments 06 The ECAT-complete packages provides additional list of electrochemical techniques supported by functionality with respect to the compact version. the instrument. The pX1000 module offers the The additional SCAN250 module provides true possibility to connect a pH sensor and tempera-linear scan cyclic voltammetry for both ring and ture sensor in order to monitor these important disk. The FRA32M module, also included, adds experimental parameters at all time elec trochemical impedance spectroscopy to the • Modular system • Waterbath control Modular Autolab PGSTAT302N can be ex pan-Software interface to external waterbath for ded with additional functionality at any time. temperature regulation • True linear scan capable • Generation collection or shielding The SCAN250 module provides unique true The rotating ring-disk electrode can be used analog scan functionality for accurate interfa-for both generation collection or shielding cial electrochemistry measurements. ex periments. • pH and temperature measurement pX1000 module provides real time monitoring of temperature and pH. 07 • Electrochemical impance spectroscopy • Analog input/output The FRA32M module extends the instrument Provides connections for analog signals and functionality with electrochemical impedance control for the Autolab motor controller. spectroscopy. • Powerful software • Electrochemical cell Advanced electrochemical NOVA 2 control Dedicated electrochemical cell for electro-software with built-in Levich and Koutecký- catalysis measurements. Levich analysis methods. Forced convection methods and experiments 08 When an electrode immersed in a solution rotates, a convective drag is created. This in turn creates drag from the bulk of the solution towards the surface of the electrode. Electroactive species are therefore transported towards Plastic body the surface of the electrode by convection and diffusion, with a diffusion layer thickness depending on the rotation rate of the electrode. The reaction products and in - ter mediates or ex cess reactant are then expelled out-wards back to the bulk of the solution. When this occurs on a rotating ring-disk electrode, an additional reaction can occur when re ac tants or products are transported over the ring. Generation/Collection experiment In the most common use of the RRDE, products formed on the disk can be detected on the ring, provided that the ring conditions are adjusted accordingly. The oxygen reduction reaction (ORR) is a classic example of this ex - perimental setup, where the ring is used to detect the formation of H O . This provides valuable insights in the 2 2 reaction pathway. Shielding experiment An alternative use of the RRDE involves two consecutive measurements. In the first measurement, only the ring is polarized and the ring current is recorded. In the second measurement, the disk is also polarized at the same po - tential. Both electrodes then compete against one another, with the disk shielding the reaction on the ring. The oxidation of NaBH provides a good illustration of 4 this use of the RRDE. 09 RRDE Cell – measurements done right Electrocatalysis experiments with noble metals and platinum in particular must be carried out in the cleanest possible conditions. With a total volume of 250 mL, the Autolab RRDE cell meets this requirement: • Easy assembly and disassembly: the cell can be easily assembled and can be completely taken apart for cleaning. • The highest chemical resistance: all parts in contact with the solution are made of materials with the best chemical resistance. These can be cleaned in the extreme conditions dictated by the experimental requirements. • Stable measurement environment: when assembled, the RRDE cell provides a stable experimental environment suitable for electrochemical measurements under reproducible laminar flow conditions. • Thermostatic jacket: the glass cell includes a thermostatic jacket for thermal control of the measurement conditions. • Two-way gas purge: the included gas purge tube can be used to saturate the solution with a gas, typically oxygen and to blanket the solution once saturated. For fast gas saturation, the gas purge generates micro-bubbles using a small glass frit. 10 RRDE – ultra-low noise rotator and controller The Autolab rotating ring-disk (RRDE) rotator uses a double, friction-less, mercury-based electrical contact for both electrodes. This ensures ultra-low noise measurements even in the most demanding experimental conditions. • Full control: the RRDE rotator can be controlled manually using the Autolab motor controller or remotely using the NOVA 2 software. • Perfect fit: the RRDE rotator is designed to fit in the matching conical fittings located in the RRDE cell. This ensures stable measurements conditions regardless of rotation rate. • Accurate control: the rotation rate can be controlled with a precision of a single rotation per minute (RPM) between 100 and 10 000 RPM, with an acceleration and deceleration rate of 4 000 RPM/s. • Compatible: the RRDE controller can be used in combination with any Autolab potentiostat/galvanostat. 11 Ring disk electrodes – the key to all experiments Electrocatalysis experiments can be conveniently carried out using the ring-disk electrode. Products and reaction intermediates created on the disk can be detected on the concentric ring under hydrodynamic conditions. • Wide rotation rate range: the ring disk electrodes are designed to be used in the full rotation rate of the Autolab RRDE rotator, from 100 RPM to 10 000 RPM. • Accurate construction: the electrodes are assembled using the most precise construction methods. A 375 µm gap between ring and disk results in a theoretical collection efficiency of 24,9%. • Different materials: the electrodes are available with glassy carbon, gold, or platinum as disk material and platinum as ring material. Autolab NOVA – Advanced electrochemistry software 12 The NOVA software is used to control all Autolab poten-Procedures for measurements with the rotating disk or tiostat/galvanostat and accessories connected to it. It the rotating ring-disk electrode are readily available. pro vides a simple and modern interface to all electroche-These methods use the remote control option of the mo - mical experiments and comes with an extensive library of tor controller to automatically scale up the rotation rate methods suitable for a wide range of applications. during the experiment, using a square root distribution. 13 NOVA provides answers in real-time. The detection of a These plots, provide information on the number of ex - reaction intermediate can be observed as the measure-changed electrons or the kinetic constant. ment proceeds. This way, a single experiment provides all of the informa-Procedures provided for rotating ring-disk measurements tion required to provide insights on the kinetics and the include data handling and data analysis commands that reaction pathway. perform the necessary steps to create Levich and Kou tecký- Levich plots alongside the experimental data re corded with the RDE or RRDE. Ordering information 14 ECAT-Compact Autolab compact electrocatalysis package Compact package for electrocatalysis measurements including: • PGSTAT204 compact potentiostat/galvanostat with monitor cable • BA dual-mode bipotentiostat module • RRDE rotator and motor controller • Glassy carbon disk/platinum ring electrode • Complete RRDE electrochemical cell • NOVA 2 advanced electrochemical software ECAT-Complete Autolab complete electrocatalysis package Complete package for electrocatalysis measurements including: • PGSTAT302N modular potentiostat/galvanostat • BA dual-mode bipotentiostat module • SCAN250 true linear scan generator module • FRA32M electrochemical impedance spectroscopy module • pX1000 pH/T measurement module • RRDE rotator and motor controller • Glassy carbon disc/platinum ring electrode • Complete RRDE electrochemical cell • NOVA 2 advanced electrochemical software • 6.0259.100 Unitrode pH and temperature sensor RRDE Cell Autolab complete RRDE cell Complete electrochemical cell for RRDE measurements including: • 250 mL glass vessel with thermostatic jacket, thermometer, adaptors, and stoppers • 6.0733.100 Ag/AgCl reference electrode, SGJ, Metrohm socket B • 6.2026.010 Support stand with support rod • PT.SHEET platinum sheet electrode, Metrohm socket B • RRDE.CAP PTFE cell cap with 7 conical fittings • RRDE.GAS two-way gas purge • RRDE.CLAMP metal cell stand holder • RRDE.ORING.SIL PTFE coated o-ring • RRDE.RING.NYLON holding ring Features ECAT-compact ECAT-complete Potentiostat/Galvanostat √ √ Bipotentiostat √ √ Electrochemical impedance spectroscopy X √ Linear scan cyclic voltammetry X √ pH and temperature measurement X √ Built-in integrator √ X Specifications and features overview Specifications PGSTAT204 PGSTAT302N Specifications (RDE and RRDE) 15 • Maximum current +/- 400 mA ± 2 A • Speed control Manual and software • Compliance voltage +/- 20 V ± 30 V • Motor speed range 100–10 000 RPM • Potentiostat yes yes • Galvanostat yes yes • Manual speed setting 100–10 000 RPM • Potential range ± 10 V ± 10 V in 1 RPM steps • Applied potential accuracy ± 0.2% ± 2 mV ± 0.2% ± 2 mV • Acceleration/ 4 000 RPM/s • Applied potential resolution 150 µV 150 µV • Measured potential resolution 3 µV (gain 100) 0.3 µV (gain 1 000) deceleration • Maximum scan rate 1 000 V/s with 1 000 V/s with • Maximum current 500 mA 15 mV step 15 mV step 250 kV/s with • Contact (RDE) Sealed Hg pool ADC10M/SCAN250 • Contact (RRDE) Double sealed Hg pool • Current ranges 100 mA to 10 nA to 10 nA (in 8 ranges) 1 A (in 9 ranges) • Electrode tips 3 mm active area in Ag, Au, • Current accuracy ± 0.2% ± 0.2% ± 0.2% of ± 0.2% of (RDE 10 mm Ø) Pt, and GC current range current range 5 mm active area in Ag, Au, • Applied current resolution 0.015% of 0.015% of current range current range Pt, GC, and empty • Measured current resolution 0.0003% of 0.0003% of • Electrode tips 5 mm active area disc in Pt, - at 10 nA range current range 30 fA current range 30 fA • Potentiostat bandwidth 1 MHz 1 MHz (RRDE 11.6 mm Ø) Au or GC and 750 µm ring • Potentiostat rise/fall time < 300 ns < 250 ns in Pt • Input impedance of electrometer > 100 GOhm // 8 pF > 1 TOhm // 8 pF • Input bias current @ 25 °C < 1 pA < 1 pA • Bandwidth of electrometer > 4 MHz > 4 MHz Specifications (BA module) • iR-compensation current interrupt and current interrupt and • Potential range +/- 10 V - resolution positive feedback positive feedback 0.025% 0.025% • Current ranges 10 mA to 10 nA, • Electrode connections 2, 3 or 4 2, 3 or 4 in 7 decades • Front panel display n.a. E and i • Current accuracy +/- 0.2% • Analog outputs (BNC) potential and current potential and current • External voltage input n.a. yes • Current resolution 0.0003% (of current range) • Analog integrator yes FI20 module • Maximum current +/- 50 mA - time constants 0.01 s, 0.1 s, 1 s, (optional) and 10 s 0.01 s, 0.1 s, 1 s, • Modes Bipotentiostat and scanning and 10 s • Interfacing USB USB bipotentiostat • A/D converter 16-bit with gains 16-bit with gains of 1, 10, and 100 of 1, 10, 100, and 1 000 • External input/output signals 1/1 2/2 • D/A converter 16-bit, 3 channels 16-bit, 4 channels • Digital I/O lines 12 48 • Dimensions (W×D×H) 15×26×20 cm3 52×42×16 cm3 • Weight 4.1 kg 18 kg • Power requirements 75 W 300 W www.metrohm.com G, CH-9100 Herisau ohm A witzerland by Metr , printed in S SW -02 Subject to modifications Layout by Ecknauer+Schoch A 8.000.5223EN – 2017