Enhancing Oxygen Reduction Reaction Catalytic Activity Using a Sub‐Stoichiometric CaTiO_3−δ Additive

Abstract

Platinum scarcity and its high cost have led to the requirement of alternative materials catalysing the oxygen reduction reaction (ORR), which is the main rate‐determining step occurring in electrochemical devices, including metal‐air batteries and fuel cells. We report a study on a sub‐stoichiometric calcium titanate (CaTiO3−δ, CTO) compound used as promoter for the ORR in order to reduce the Pt loading and improve its electrocatalytic activity. Composite catalysts based on Pt/C with different amounts of CTO were prepared and their activity was investigated by rotating disk electrode (RDE). The obtained results proved a higher catalytic activity for the composite electrode, with respect to pure Pt/C, in terms of electrochemically active surface area, oxygen reduction current density, onset potential and stability.

Performance Improvement in Direct Methanol Fuel Cells by Using CaTiO3-δ Additive at the Cathode

“…The polarization and power density curves recorded for the two MEAs are reported in Figure 3 at three different temperatures (30, 60 and 90°C), feeding the anode with a 2 M methanol solution. From the polarization behavior at the different temperatures, it appears that the presence of the CTO additive promotes the oxygen reduction reaction, as already demonstrated by a previous work dealing with ex-situ RDE analysis [37]. In fact, by comparing the behavior at all investigated temperatures, the composite-electrode-based MEA showed a lower loss of potential in all the regions of the polarization curve, but, in particular, in the activation and ohmic regions.…”

“…[38][39][40][41][42]. In this case, it appears that the presence of a substoichiometric CTO increases the ECSA due to a local coordination of CTO particles with Pt [37]. As reported in a previous paper [37], the composite material presents a higher electrochemical active surface area (ECSA) compared to the bare Pt/C (74 vs. 57 m 2 g −1 ), as determined by cyclic voltammetry (CV).…”

“…The images show a homogeneous distribution of the two compounds, with a prismatic, quasi-cubic shape of the CTO particles and the porous structure of the Pt/C catalyst (the typical morphology of carbon black can be observed in Figure 2a). As reported in a previous paper [37], the composite material presents a higher electrochemical active surface area (ECSA) compared to the bare Pt/C (74 vs. 57 m 2 g −1 ), as determined by cyclic voltammetry (CV). This indicates that the mixing procedure does not create agglomeration of particles, but helps with increasing the interface and Pt utilization.…”

“…[38][39][40][41][42]. In this case, it appears that the presence of a substoichiometric CTO increases the ECSA due to a local coordination of CTO particles with Pt [37]. The catalyst and the CTO additive were mixed together (in an ultrasonic bath) in a weight ratio of 1:1.…”

“…This material, prepared by using a solvo-thermal method, has been recently investigated as a promoter of Pt/C catalysts for the ORR in rotating disk electrode (RDE), showing increased activity. The catalytic enhancement has been attributed to the presence of oxygen vacancies in the CTO structure, acting as available active sites for oxygen adsorption, facilitating a faster ORR [37]. In the present work, the most promising composite catalyst formulation (Pt/C:CTO 1:1) has been investigated at the cathode of a DMFC in order to increase the performance.…”