Hydrogen Oxidation and Evolution Reaction Kinetics on Carbon Supported Pt, Ir, Rh, and Pd Electrocatalysts in Acidic Media

Abstract

The hydrogen oxidation and evolution reaction (HOR/HER) behavior of carbon supported metal (Pt, Ir, Rh, Pd) nanoparticle electrocatalysts is studied using the H 2 pump approach, in a proton exchange membrane fuel cell (PEMFC) setup. After describing the best method for normalizing the net faradaic currents to the active surface area of the electrodes, we measure the HOR/HER kinetic parameters (exchange current densities and transfer coefficients) in a temperature range from 313 K to 353 K and calculate the activation energy for the HOR/HER process. We compare the measured kinetic parameters with those extracted from different mass-transport limitation free setups in literature, to evaluate the hydrogen electrocatalysis on these most active surfaces. The HOR/HER activity scales with the following: Pt > Ir Rh > Pd. The anodic and cathodic transfer coefficients are similar for all metals (ca. 0.5), leading to Tafel In the current view of energy conversion based on the use of fuel cells and electrolyzers, the hydrogen electrocatalysis plays a central role. H 2 is used as a fuel in proton exchange membrane fuel cells (PEMFCs), where it is electrochemically oxidized at the anode electrode according to:In PEMFC anode electrode, only small amounts of Pt (ca. 0.05 mg Pt /cm 2 geo ) are required to catalyze the hydrogen oxidation, without contributing to any efficiency loss of the overall fuel cell performance.1 The same would hold true for the hydrogen evolution reaction -HER -at the cathode side of water electrolyzer systems. Moreover, except when considering contamination issues e.g. due to the presence of CO in reformate hydrogen, or stability issues e.g. due to hydrogen starvation events mode, a replacement of the current carbon supported platinum (Pt/C) based electrode technology is not contemplated in PEMFC. 2 The drawback of both PEM-based fuel cells and electrolyzer systems arise from the large amounts of noble metal (ca. ≈0.4 mg metal /cm 2 geo ) required to catalyze at acceptable rates the sluggish oxygen reduction reaction (ORR) in fuel cell cathodes, and the oxygen evolution reaction (OER) in electrolyzer anodes. [3][4][5] Contrary to the acidic PEM-based technologies, anion exchange membrane (AEM) based devices, [6][7][8] which are operating at high pH, offer the use of cost-effective non-noble metal electrodes to catalyze the ORR 9,10 and OER 11-13 at almost similar rates than on noble metal electrodes in acidic electrolytes. As a result, a replacement of PEMbased devices by AEM ones will be advantageous 14 if and only if AEM conductivities will be further increased to the level of PEM, 15,16 and their sensitivity to CO 2 significantly reduced. 17 However, getting rid of the noble metal contents in AEM-device electrodes would be feasible only in the case of similar hydrogen oxidation and evolution reaction (HOR/HER) rates in AEMs versus PEM-based conversion devices. Unfortunately, recent studies have shown that the HOR/HER rates of noble metal electrodes in the alkaline environment are much slower than in ...

Size-Dependent Hydrogen Oxidation and Evolution Activities on Supported Palladium Nanoparticles in Acid and Base

“…The exchange current density determined using a H 2 -pump in a proton exchange membrane fuel cell configuration (which resembles that in electrolyte with pH = 0) is 5.2 ± 1.2 mA/cm 2 Pd at 313 K, 1 which can be converted to 2.3 ± 0.5 mA/cm 2 Pd at 293 K according to Arrhenius equation with an activation energy of 31 kJ/mol. 27 The excellent agreement in the exchange current densities measured using RDE in this work and H 2 -pump indicates the validity of RDE method to characterize HOR/HER activity on Pd/C in acid.…”

“…5), which could appear as an extra oxidation peak in the polarization curve. 13,27 Pd − H bulk ↔ Pd − H upd [5] Smaller or no extra peaks associated with oxidation of absorbed hydrogen were observed in the polarization curves in 0.1 M KOH (Figure 5a), which might be attributed to the slow HOR reaction and the slow scanning rate used in the measurement to allow the absorbed hydrogen to diffuse back to the surface to be reacted as H upd . In 0.1 M HClO 4 , there indeed exists absorbed hydrogen oxidation peaks in the polarization curves for Pd/C-300C, Pd/C-400C, Pd/C-500C and Pd/C-600C at about 0.069 V, 0.079 V 0.086 V and 0.134 V, respectively (Figure 5b).…”

“…Similar correlation between the activation energy and the exchange current density on Pt/C, Pd/C and Ir/C is also valid in acid. 27 Therefore, the higher Pd-H binding energy in base is likely responsible for the lower HOR/HER activity.…”

Electrocatalysts for hydrogen oxidation and evolution reactions

“…However, for some catalysts with ultra-high activity (e.g., Pt in acid environment), mass transport remains a problem, even when the RDE technique is used [14,15]. The polarization curve approaches the diffusional overpotential curve (described by Equation (4)); thus, the error in the calculation of i k becomes non-negligible, and i 0 is often underestimated.…”

Recent Progress in Nanoparticle Synthesis via Liquid Medium Sputtering and its Applications

“…Moreover, in NPs, quantum effects can change or enhance properties such as reactivity, strength, and electrical characteristics [4]. Besides the ORR, NPs can catalyze many electrochemical reactions, including the hydrogen evolution [5,6], liquid fuel (e.g., methanol [7,8], ethanol [9,10] and formic acid [11,12]) oxidation, and carbon dioxide reduction reactions [13].…”