Developing Robust Electrocatalysts for Oxygen Evolution in Alkaline Seawater Electrolysis (ASWEs)

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Abstract

Through the recently concluded Network-H2 (EPSRC) flexible funded SEAVOLT project, and the ongoing RED (Research England Development) funded projects on Alkaline Seawater Electrolysis, we, at Teesside University (in collaboration with Durham U.), have initiated the exploration of Metal Organic Framework (MOFs) as anodic electrocatalysts. MOFs have high surface area, and can be extremely tuneable towards high oxidation activity, offering high degree of freedom towards inducting a range of Transition Metal (TM) ions. The performance of these materials has also been compared with well-known Layered Double Hydroxides (LDHs) synthesized in the laboratory. We present the details of synthesis, characterization, and performance evaluation of BDC, BTC, and ZIF ‘pristine’ MOFs, with combinations of Ni, Fe, Co, Cu and Zn. Synthetic methods like hydrothermal synthesis of MOFs and LDHs, a one-pot synthesis and coating on Ni-foams, ion-exchange of dopant cations (for MOFs), electrodeposition and dip coating (LDHs), were accomplished in this project. XRD, XPS, SEM and TEM (SAD) analysis have been used to probe the crystallinity, oxidation state, morphology, and crystallographic planes, respectively. TEM micrographs provided great insight into the average inter-layer spacing of the LDHs, viz., 1-1.25 nm. XRDs confirmed the layered structure, and also demonstrated loss of crystallinity at very high levels of dopant cations like Fe. Highly crystalline structures are also reflected by high surface area flower-like 2-d morphologies (both MOFs and LDHs), similar to that observed in certain literature, indicating that these are the desirable morphologies that can generate high Electrochemical Surface Areas.
Notable observations based on these highly microporous materials were as follows – Ni-based structures on their own are not very effective but doping them (particularly with Fe) in an optimal quantity enabled much higher kinetics (lower overpotential, low Tafel slopes), while retaining the crystalline layered structure. This trend persists for not only LDH materials but also MOF (Ni Fe-BDC). What was interesting to note that Cyclic Voltammetry showed marked changes in the oxidation peaks of the Ni-Fe ions, with Fe apparently suppressing further Ni oxidation (similar observations have been reported in literature) – the suppression of excessive Ni oxidation appears to result in the decrease in overpotential, lower Tafel slopes and intercepts, thus confirming the performance boost. Catalytic activity has been established to be a strong function of doping of Ni with Fe, Cu, Co, over a range of microporous structures, viz., LDH and MOFs. Preliminary studies on the synthesis and testing of ternary transition metal combinations for both Layered Double Hydroxides (LDHs) and for MOFs have showed them to be effective, as catalysts, and offering the scope for considerable further optimization.
However, the overall poor catalytic performance reflected in BTC MOFs which otherwise have a strong crystallinity and prominent 2-d and 3-d nano-structures, may also be limited by poor electron transfer, i.e., poor electronic conductivity. This is a subject that needs more detailed probing. The combination of MOFs/ LDHs with an electronic conducting phase like graphene or graphitic inks is also being investigated.
This work is funded by EPSRC Network for Hydrogen Fuelled Transportation (Network-H2) flexible fund award and is a collaborative work between Teesside University and Durham University. MOF structures continue to be investigated by the RED funded projects taking place at the Net Zero Ctr at Teesside University, in collaboration with Durham U.
Original languageEnglish
Pages132-133
Number of pages2
Publication statusPublished - 12 Sept 2024
EventElectrochem2024 - Manchester Metropolitan University, Manchester, United Kingdom
Duration: 11 Sept 202413 Sept 2024
https://www.rsc.org/events/detail/79233/electrochem2024

Conference

ConferenceElectrochem2024
Country/TerritoryUnited Kingdom
CityManchester
Period11/09/2413/09/24
Internet address

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