Engineering topics

Kumaraguru, Swami (ORCID:0000000286442074)

Publications and source records attributed to Kumaraguru, Swami (ORCID:0000000286442074).

4 records

DOE OSTI2023

Engineered Catalyst Support with Improved Durability at Higher Weight Percentage of Platinum

Proton Exchange Membrane (PEM) fuel cells are a suitable electrochemical power source for heavy duty vehicle (HDV) applications due to their high efficiency and durability. The cathode of the fuel cell uses a higher geometric loading of platinum (∼0.2 to 0.4 mg Pt /cm 2 ) for the electrocatalysis of the kinetically sluggish Oxygen Reduction Reaction (ORR) which requires higher weight percent loading of the metal (∼50%) on the carbon support to decrease the catalyst layer thickness and hence, the reactant transport losses. The conventionally used supports for platinum catalyst, such as the KetjenBlack TM type high surface area carbon (HSC) features limited mesopore area for the dispersion of Pt nanoparticles leading to increased aggregation and poor durability. Here, we show a new class of carbon materials known as the Engineered Catalyst Support (ECS) developed by Pajarito Powder with higher mesopore fraction for the dispersion of higher weight percentage of Pt nanoparticles. ECS materials can disperse up to 50% Pt by weight of the catalyst thereby enabling lower catalyst layer thickness with higher performance retained after durability test. A comprehensive set of physico-chemical and electrochemical studies in membrane electrode assembly (MEA) are reported to understand the performance and durability of Pt/ECS catalysts.

08 HYDROGEN↗

DOE OSTI2023

Do Melamine and Melamine-Formaldehyde Surface Modifiers Improve Fuel Cell Activity and Durability?

Precious group metal-based catalysts based on Pt- and Pt-alloys are currently used as catalysts for the kinetically sluggish Oxygen Reduction Reaction (ORR) on the cathode of fuel cells. The activity of Pt or Pt-alloy catalysts towards ORR is severely compromised by the adsorption of spectator-species such as sulfonate anions from perfluorosulfonic acid (PFSA) ionomer or Pt-O(H) ad via water activation. Considering recent evidence pointing to the improvement in ORR activity via the use of melamine organic molecule or melamine-formaldehyde copolymeric additives as surface blocking agents for the prevention of sulfonate or Pt-OH ad adsorption, we evaluated these additives in fuel cells. The catalysts were modified with either of these additives and characterized using ex situ and in situ methods to verify successful adsorption and eventual performance in fuel cells. These surface modifying agents were found to suppress Pt-OH ad formation as well as suppress ORR activity. There was no evidence to point out that these additives improved ORR activity and H 2 /air polarization performance in a fuel cell MEA on supported, polycrystalline Pt catalyst.

08 HYDROGEN↗

DOE OSTI2023

Improving Durability of Fuel Cells with Platinum-rich Alloy Cathode Catalysts

Pt 3 Co-alloy based nanoparticle catalysts are very active for oxygen reduction reaction (ORR) thereby enabling high performance of proton exchange membrane fuel cells (PEMFC) for automotive propulsion. However, these catalyst materials degrade due to a combination of electrochemical surface area (ECSA) loss and dissolution of cobalt-alloying element from the nanoparticles. Dissolution of cobalt has a two-fold impact on the durability of fuel cells—i) a loss in the low-current density kinetic region due to a decrease in specific activity and ii) a loss in the high-current density transport region due to Co 2+ contamination of the ionomer phase. Cobalt dissolution-contamination needs to be mitigated as it limits fuel cell performance and lifetime for heavy-duty automotive applications. In this article, we study the use of PtCo-alloy catalysts with Pt-rich compositions using catalyst-specific accelerated stress test measurement in membrane electrode assemblies to decrease the amount of dissolved Co and mitigate its subsequent contamination effects. We demonstrate Pt 5 Co and Pt 7 Co compositions to enable significant improvements in durability (∼50 mV and ∼100 mV with respect to Pt 3 Co after 30,000 voltage cycles) with a minor but acceptable compromise in the initial specific activity of the catalyst.

08 HYDROGEN↗

DOE OSTI2021

Mitigation of PtCo/C Cathode Catalyst Degradation via Control of Relative Humidity

Maintaining the high performance of proton-exchange membrane fuel cells (PEMFC) over the course of its lifetime is a key enabling factor for its successful commercialization as a primary power source in zero-emission transportation applications. In this context, it is important to mitigate the degradation of PtCo-alloy based cathode catalysts used for oxygen reduction reaction (ORR). PtCo-alloy catalysts exhibit high activity at beginning-of-life (BOL) which tends to decrease during operation due to loss of electrochemical surface area (ECSA) and dissolution-contamination related effects of the Co-alloying component. Here, we demonstrate the use of relative humidity (RH) of the inlet gases as a controllable parameter to mitigate the degradation of PtCo-alloy catalyst degradation. We employ a catalyst-specific voltage cycling accelerated stress test (AST) durability protocol as a function of inlet RH to degrade PtCo catalysts. A series of in situ electrochemical diagnostics and ex situ characterizations have been carried out to investigate the catalyst layer characteristics at end-of-test (EOT). Our results show that at sub-saturated conditions of durability protocol operation, PtCo catalyst sustains higher EOT H 2 /air performance due to better retention of ECSA and smaller impact of Co 2+ dissolution/contamination.

25 ENERGY STORAGE↗