Fundamentals of Electrocatalysis

Krischer, Katharina; Savinova, Elena R.

doi:10.1002/9783527610044.hetcat0101

Cited by 25 publications

(31 citation statements)

References 122 publications

(155 reference statements)

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“…Photo-electrocatalytic H2 generation at a rate (ωH2) of ca 80 nmol hour -1 cm -2 was achieved with this photocathode in In mechanism I, the dye monolayer is hypothesized to sustain H-H bond formation via classical Volmer-Heyrovsky or Volmer-Tafel schemes. 29 In a Volmer step, H + from solution is reduced to H • by a photo-generated electron on the dye surface. In a subsequent Heyrovsky step (Scheme 1: mechanism I, teal), a second photo-generation event, involving a second H + , leads to the formation of H2.…”

Section: Introductionmentioning

confidence: 99%

Origin of Photoelectrochemical Generation of Dihydrogen by a Dye-Sensitized Photocathode without an Intentionally Introduced Catalyst

et al. 2017

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Dye-sensitized photocathodes have been observed on several occasions to sustain light-driven H 2 generation without intentionally introduced catalysts. Herein, plausible mechanisms addressing this phenomenon are probed by a combination of long-term photoelectrochemical measurements with concurrent gas chromatography, transient absorption spectroscopy, and inductively coupled mass spectrometry using a perylenemonoimide-sexithiophene-triphenylamine (PMI-6T-TPA) sensitized NiO electrode. The experimental evidence obtained discounts the possibility for direct reduction of hydrogen by the dye and demonstrates that the availability of interfaces between dye molecules and any electrically disconnected NiO particles exposed to the electrolyte solution is critical for photoelectrocatalytic H 2 generation. These interfaces are postulated to serve as photoactive sites for the formation of a hydrogen evolution catalyst, e.g., metallic nickel, which can accept photogenerated electrons from the excited dye molecules. The Ni 0 catalyst can form via photoelectroreduction of Ni 2+ , which has been found to slowly dissolve from the NiO support into the solutions during the photoelectrochemical measurements. Additionally, dependence of the H 2 generation rate on the anion within the electrolyte has been identified, with the highest rates of 35-40 nmol h -1 cm -2 achieved with acetate. The origin of this dependence remains unsolved at this stage but is clearly demonstrated to be not associated with the different rates of dissolution of NiO, the presence of other transition metal contaminants, nor electronic impacts of the anion on the NiO valence band. Overall, the results herein demonstrate that the effects of the chemical nature of the electrolyte, metallic nickel deposited from dissolved Ni 2+ , and availability of the interfaces between disconnected NiO and adsorbed dye should be considered when interpreting the photoelectrocatalytic performance of dye-sensitized photocathodes for dihydrogen evolution. × Our colleague, mentor and friend Prof. Leone Spiccia has passed away before this work could be published. Leone was an outstanding researcher and personality, and is sadly missed. ABSTRACTDye-sensitized photocathodes have been observed on several occasions to sustain light-driven H2 generation without intentionally-introduced catalysts. Herein, plausible mechanisms addressing this phenomenon are probed by a combination of long-term photo-electrochemical measurements with concurrent gas chromatography, transient absorption spectroscopy and inductively coupled mass spectrometry using a perelenmonoimid-sexithiophene-triphenylamine (PMI-6T-TPA) sensitized NiO electrode. The experimental evidence obtained discounts the possibility for direct reduction of hydrogen by the dye and demonstrates that the availability of interfaces between dye molecules and any electrically-disconnected NiO particles exposed to the electrolyte solution is critical for photo-electrocatalytic H2 generation. These interfaces are postulated to serve as photo-a...

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Section: Introductionmentioning

confidence: 99%

Origin of Photoelectrochemical Generation of Dihydrogen by a Dye-Sensitized Photocathode without an Intentionally Introduced Catalyst

et al. 2017

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“…This is mainly due to the fact that the water splitting reaction is a kinetically controlled process characterized by slow charge transfer and insufficient chemical reaction rates, and in reality, a significantly higher overpotential than the standard potential of the water electrolysis (−1.23 V at 25 °C) needs to be applied to drive the reaction. 4 Therefore, electrocatalysts are used to facilitate water electrolysis by reducing the value of the applied overpotential to conduct cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), which are the key half reactions of electrochemical water splitting. 4 The best performing and long lasting electrocatalysts for HER and OER are Pt and IrO 2 , respectively.…”

Section: Introductionmentioning

confidence: 99%

“…4 Therefore, electrocatalysts are used to facilitate water electrolysis by reducing the value of the applied overpotential to conduct cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), which are the key half reactions of electrochemical water splitting. 4 The best performing and long lasting electrocatalysts for HER and OER are Pt and IrO 2 , respectively. [5][6] Also, other platinum group metals (PGMs) and PGM-containing compounds show high electrocatalytic performance in water electrolysis.…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic Performance and Stability of Nanostructured Fe–Ni Pyrite-Type Diphosphide Catalyst Supported on Carbon Paper

et al. 2016

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A simple and effective method to prepare an active and stable nanostructured working electrode for electrochemical water splitting is described. Specifically, mixed Fe-Ni diphosphide was prepared by sputtering a 200-nm-thick layer of Permalloy onto carbon paper gas diffusion layer followed by gas transport phosphorization reaction. The mass density of the resultant diphosphide phase was established to be 1.1 mg/cm 2. Energy-dispersive X-ray microanalysis shows that the actual elemental composition of the resultant ternary electrocatalyst is approximately Fe 0.2 Ni 0.8 P 2 , while the powder X-ray diffraction analysis confirms that the electrocatalyst crystallizes in NiP 2 cubic pyrite-like structure. As a cathode for hydrogen evolution reaction (HER) in acidic and alkaline electrolytes, this earth-abundant electrode has exchange current densities of 6.8410 3 and 3.1610 3 mA/cm 2 and Tafel slopes of 55.3 and 72.2 mV/dec, respectively. As an anode for oxygen evolution reaction (OER) in alkaline electrolyte, the electrode shows an exchange current density of 2.8810 4 mA/cm 2 and Tafel slope of 49.3 mV/dec. The observed high activity of the electrode correlates well with its electronic structure, which was assessed by density functional theory (DFT) calculations. The stability of Fe 0.2 Ni 0.8 P 2 electrocatalyst in HER and OER was evaluated by means of accelerated degradation test and chronopotentiometry. The results of these experiments elucidate partial dissolution and entire chemical transformation of Fe 0.2 Ni 0.8 P 2 as the main mechanisms of the electrode degradation during HER and OER, respectively. Overall, our findings could facilitate the composition-based design of active, stable, and durable phosphide electrodes for electrochemical water splitting.

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“…are consistent with a hydrogen dissociative adsorption rds. 23,24 The average Tafel slope for the monometallic Pt catalyst at all of the pH values measured was 127 ± 18 mV/dec. while the average Tafel slopes for the Ru-containing catalysts were 31 ± 3, 30 ± 7, and 30 ± 4 mV/dec.…”

Section: Resultsmentioning

confidence: 93%

The Effect of Carbonate and pH on Hydrogen Oxidation and Oxygen Reduction on Pt-Based Electrocatalysts in Alkaline Media

John

Atkinson

Roy

et al. 2016

J. Electrochem. Soc.

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We investigated the performance of several carbon-supported Ru x Pt y electrocatalysts for their alkaline hydrogen oxidation and oxygen reduction performance in the presence of carbonate and compared their performance with monometallic, carbon-supported Pt. Our results indicate a strong dependence of HOR upon pH for the monometallic Pt catalysts (22 mV/pH) and a weak dependence upon pH for the Ru-containing electrocatalysts (3.7, 2.5, and 4.7 mV/pH on Ru 0.2 Pt 0.8 , Ru 0.4 Pt 0.6 , and Ru 0.8 Pt 0.2 , respectively). These results are consistent with our previous findings that illustrate a change in rds from electron transfer (on monometallic Pt) to dissociative hydrogen adsorption (on Ru x Pt y catalysts). Analysis of the kinetic currents to determine the rate-determining step via Tafel slope analysis provides additional data supporting this conclusion. There is no difference in the performance at comparable pH values in the presence or absence of carbonate on monometallic Pt indicating that water/hydroxide is the primary proton acceptor for alkaline HOR in 0.1 M KOH aqueous electrolyte. Finally, we observe no pH or carbonate dependence for the ORR on Ruthenium-platinum nanomaterials are currently the best performing alkaline hydrogen oxidation reaction (HOR) catalysts in fuel cells.1 Their improved activity vs. platinum has been realized through the understanding and application of ligand and bi-functional effects to reduce the metal-hydrogen, M-H, binding energy of Pt and to improve H ads reactivity with adsorbed hydroxyl groups, OH ads . [1][2][3][4] Hydrogen oxidation on Pt electrocatalyst is sensitive to pH because the rate-determining step is concerted electron/proton transfer (Volmer/Heyrovsky step).3,5 However, we have demonstrated on RuPt alloy catalysts that the rds changes to the pH-insensitive hydrogen dissociative adsorption (Tafel step). The impact of pH and carbonate on Ru-Pt alloy catalysts, consequently, remains unresolved for HOR in an alkaline environment.It is well documented that carbon dioxide in air partitions into the aqueous alkaline electrolyte at the cathode as carbonate and is purged at the anode during fuel cell operation.6-8 Carbonate has not been demonstrated to poison the anode catalyst; however, alkaline carbonate has been proposed as an active proton acceptor, 9 according to Eq. 1, competitive with hydroxide, Eq. 2.It has been suggested by some authors that because of water's ability to rapidly self-associate/dissociate that it is an active participant in the oxidation of H ads during alkaline hydrogen oxidation. Water is the major component of the electrolytic environment in both traditional, three-electrode electrochemical cells and in solid polymer electrolyte fuel cells. Consequently, if water is an active participant in the HOR, concentration effects should mask the contribution of carbonate. Resolving this question has important implications for modeling the alkaline fuel cell environment, as well as developing improved catalysts. * Electrochemical Society Active Member.*...

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Fundamentals of Electrocatalysis

Abstract: The sections in this article are Introduction The Electrical Double Layer and Potentials The Electrical Double Layer The Work Function of an Electrode, the Electrode Potential and the Potential of Zero Charge Potentials in Galvanic or Electrolytic Cells Electrode Kinetics Kine… Show more

Cited by 25 publications

References 122 publications

Origin of Photoelectrochemical Generation of Dihydrogen by a Dye-Sensitized Photocathode without an Intentionally Introduced Catalyst

Origin of Photoelectrochemical Generation of Dihydrogen by a Dye-Sensitized Photocathode without an Intentionally Introduced Catalyst

Electrocatalytic Performance and Stability of Nanostructured Fe–Ni Pyrite-Type Diphosphide Catalyst Supported on Carbon Paper

The Effect of Carbonate and pH on Hydrogen Oxidation and Oxygen Reduction on Pt-Based Electrocatalysts in Alkaline Media

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