Nanometric Fe-Substituted ZrO₂on Carbon Black as PGM-Free ORR Catalyst for PEMFCs

Abstract

In this contribution, we demonstrate the presence of high-spin Fe 3+ in Fe-substituted ZrO 2 (Fe x Zr 1−x O 2−δ), as deduced from X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and 57 Fe Mössbauer spectroscopy measurements. The activity of this carbon-supported Fe x Zr 1−x O 2−δ catalyst toward the oxygen reduction reaction (ORR) was examined by both rotating (ring) disk electrode (R(R)DE) method and single-cell proton exchange membrane fuel cells (PEMFCs). DFT calculations suggest that the much higher ORR mass activity of Fe x Zr 1−x O 2−δ compared to Fe-free ZrO 2 is due to the enhanced formation of oxygen vacancies: their formation is favored after Zr 4+ substitution with Fe 3+ and the oxygen vacancies create potential adsorption sites, which act as active centers for the ORR. H 2 O and/or H 2 O 2 production observed in RRDE measurements for the Fe 0.07 Zr 0.93 O 1.97 is also in agreement with the most likely reaction paths from DFT calculations. In addition, Tafel and Arrhenius analyses are performed on Fe 0.07 Zr 0.93 O 1.97 using both RRDE and PEMFC data at various temperatures.

Proton Exchange Membrane Fuel Cells (PEMFCs): Advances and Challenges

“…The specifications for a fuel cell system consist of establishing the performance, dimension, weight and size, emissions, output power, rapid start-up, and rapid response to changes in load, lifetime, and operability in intense environments and noise, which play an important role in certain applications. Great attention has been paid to replacing platinum group metals with carbon-based non-precious metal, nanoporous metals [ 333 , 334 , 335 ], heteroatom-doped carbons [ 336 ], covalent organic frameworks [ 337 , 338 ], non-precious metal, or precious-metal-free catalysts of inexpensive metals [ 339 , 340 , 341 ] as a promising new generation of electrocatalysts has emerged. This is due to their reduced cost, enhanced performance, and high stability and activity of fuel cell applications.…”

Stability and Activity of Cobalt Antimonate for Oxygen Reduction in Strong Acid

“…These catalysts pose a challenge of simultaneously realizing activity and stability, as evidenced by the ZrO x catalyst on glassy carbon exhibiting cathodic current density below 5 μA cm –2 at 0.7 V vs RHE . Optimization of catalyst electrodes by using conductive graphitic carbon materials, ,− controlling the nanoparticle size, and/or increasing the oxygen vacancy density − can increase the cathodic current density up to 0.2 mA cm –2 at 0.7 V vs RHE. The CoSb 2 O 6 catalyst of the present work (at ambient temperature) exhibits 30× higher current density with 100× lower dissolved metal concentration compared to ZrO x on glassy carbon, motivating further study of whether analogous optimization of electrode synthesis could elevate the current density of CoSb 2 O 6 -based catalysts.…”

Platinum Group Metal-Free Catalysts for Oxygen Reduction Reaction: Applications in Microbial Fuel Cells

“…Moreover, Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), atomic force microscopy, and transmission electron microscopy (TEM) allow achieving insights into catalyst morphology. This combined characterization allows evaluating catalyst performance by simulating operational conditions and selecting the best catalyst material for test in a complete system [60][61][62].…”

“…Catalysts 2020, 10, x FOR PEER REVIEW 7 of 22 catalyst performance by simulating operational conditions and selecting the best catalyst material for test in a complete system [60][61][62].…”