Cathode catalysts in polymer electrolyte membrane fuel cells (PEMFCs) are often supported by carbon, which is susceptible to corrosion at operating potentials. Transition metal carbides (TMCs) are a class of material that could be used as catalyst supports to replace carbon as they are electrically conductive and can be resistant to corrosion. TMCs which show promising activity for the oxygen reduction reaction (ORR) have been shown to suffer from oxidation and dissolution, whereas corrosion-resistant carbides tend to have significantly lower ORR activities. Here we used co-reduction carburization to synthesized alloys of Mo 2 C and TaC with the aim of designing a carbide support that was both active and corrosion resistant. The addition of 15 mol% Ta to the precursor mixture used to synthesize the alloy support increased the corrosion potential by nearly 150 mV and decreased the corrosion current to 16% of that observed in the Ta-free support. While Ta-alloyed Mo 2 C supports had reduced ORR activity compared to their Ta-free counterparts, the Ta-alloyed supports performed favorably when compared to Vulcan XC-72. We show that further improvements to alloy-carbide based supports can be achieved by modulating the structure of the catalyst particles from Pt to Pt 3 Ni. Furthermore, density functional theory (DFT) calculations can be used to predict oxygen binding and corrosion resistance in digitally designed alloy carbides.
Owing to its high energy density, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC811) is a cathode material of prime interest for electric vehicle battery manufacturers. However, NMC811 suffers from several irreversible parasitic reactions that lead to severe capacity fading and impedance buildup during prolonged cycling. Thin surface protection films coated on the cathode material mitigate degradative chemomechanical reactions at the electrode−electrolyte interphase, which helps to increase cycling stability. However, these coatings may impede the diffusion of lithium ions, and therefore, limit the performance of the cathode material at a high C-rate. Herein, we report on the synthesis of zirconium phosphate (Zr x PO y ) and lithium-containing zirconium phosphate (Li x Zr y PO z ) coatings as artificial cathode−electrolyte interphases (ACEIs) on NMC811 using the atomic layer deposition technique. Upon prolonged cycling, the Zr x PO y -and Li x Zr y PO zcoated NMC811 samples show 36.4 and 49.4% enhanced capacity retention, respectively, compared with the uncoated NMC811. Moreover, the addition of Li ions to the Li x Zr y PO z coating enhances the rate performance and initial discharge capacity in comparison to the Zr x PO y -coated and uncoated samples. Using online electrochemical mass spectroscopy, we show that the coated ACEIs largely suppress the degradative parasitic side reactions observed with the uncoated NMC811 sample. Our study demonstrates that providing extra lithium to the ACEI layer improves the cycling stability of the NMC811 cathode material without sacrificing its rate capability performance. KEYWORDS: LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), metal phosphate, atomic layer deposition (ALD), surface passivation, suppressed parasitic reactions, high rate performance
The synthetic control through colloidal synthesis led to a remarkable increase in platinum mass activity in octahedral nanocrystals with Pt-rich surface. In this manuscript, we demonstrate that the ratio of...
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