Synthesis of shape-controlled Pt-alloy nanocatalysts for the hydrogen-bromine redox flow battery
Available from 14-11-2022.
Contact: Max Berkers (firstname.lastname@example.org)
The electricity grid of the future will comprise a high percentage of ‘intermittent’ renewable electricity generation in the form of solar and wind energy. Society will therefore also need vast amounts of energy storage capacity to deliver renewable electricity even during hours of low wind and solar irradiation. The most important parameters for large-scale storage to compete with fossil generation are the cost of storage (which includes material cost, energy efficiency and battery lifetime) and scalability. The hydrogen-bromine redox flow battery is one of the best candidates to fulfil this role, owing to the low cost of electroactive materials, long lifetime, high roundtrip efficiency, and high energy density.[1, 2]
Figure 1: schematic representation of a H2-Br2 RFB.
During battery charging, hydrobromic acid is pumped from an external tank into the cell, where on the ‘liquid side’ bromide ions (Br-) are oxidized to bromine (Br2). Meanwhile, protons diffuse through the proton-exchange membrane separator to the ‘hydrogen side’, where protons (H+) are reduced to hydrogen gas (H2). During battery discharge these reactions are reversed. The hydrogen reactions are catalyzed by nanoparticles made of platinum, which is a scarce and expensive metal (with a price of 40 USD/g as of February 2021), which can represents a sizeable percentage of the cell cost. Furthermore, unwanted cross-over from bromine species to the hydrogen side can accelerate the degradation of the catalyst, limiting the battery lifetime. Therefore, an improved catalyst for the hydrogen reactions with both high catalytic activity and high stability in extremely corrosive electrolyte is urgently needed.
Earlier work has shown that alloying Pt with a second metal (e.g. Cu, Ni, Ir) can improve the cost-benefit analysis by lowering the amount of required Pt without compromising catalytic activity, and can even improve durability by lowering the affinity of Pt for bromine adsorption. Another promising approach is the design of nanoparticles with well-defined morphology. Studies on single crystals have shown that among the three low-index fcc planes (111), (100) and (110), the (111) facets exhibit the slowest dissolution. Therefore, Pt nano-catalysts with a tetra- or octahedral shape, which exposes exclusively (111) surfaces, have been shown to degrade more slowly than commercial nanoparticles of uncontrolled shape.
In this project, the student will combine these two approaches and synthesize shape-controlled Pt and Pt-alloy nanoparticles via solvothermal synthesis or other methods. These nanoparticles will then be characterized via a variety of microscopic (e.g., SEM, TEM) and spectroscopic techniques (e.g., XRD, XRR, XPS), as well as via electroanalytical methods such as voltammetry, impedance spectroscopy and corrosion studies. The goal of the project is the successful synthesis of shape-controlled Pt-alloy nanoparticles and the quantification of their electrocatalytic performance and stability. Promising leads will also be tested at larger scale under real world conditions at the industrial partner Elestor B.V.
1. Hugo, Y.A., et al., Techno-Economic Analysis of a Kilo-Watt Scale Hydrogen-Bromine Flow Battery System for Sustainable Energy Storage. Processes, 2020. 8(11).
2. Cho, K.T., et al., Cyclic Performance Analysis of Hydrogen/Bromine Flow Batteries for Grid-Scale Energy Storage. Chempluschem, 2015. 80(2): p. 402-411.
3. Saadi, K., et al., Crossover-tolerant coated platinum catalysts in hydrogen/bromine redox flow battery. Journal of Power Sources, 2019. 422: p. 84-91.
4. Liu, Q., et al., On the Stability of Pt-Based Catalysts in HBr/Br-2 Solution. Helvetica Chimica Acta, 2021.
5. Lopes, P.P., et al., Relationships between Atomic Level Surface Structure and Stability/Activity of Platinum Surface Atoms in Aqueous Environments. Acs Catalysis, 2016. 6(4): p. 2536-2544.
6. Rana, M., et al., High-Yield Synthesis of Sub-10 nm Pt Nanotetrahedra with Bare < 111 > Facets for Efficient Electrocatalytic Applications. Acs Applied Materials & Interfaces, 2015. 7(8): p. 4998-5005.