Seacat - Catalysts for Direct Seawater Electrolysis

Abstract

With current technology, the direct electrolysis of seawater struggles with ACSFRs (active chlorine species formation reactions), including the ClER (chlorine evolution reaction), competing with the formation of gaseous oxygen on the anode side. The corrosive and poisonous chlorine compounds produced in the ClER pose a significant issue, essentially destroying the electrolyser in a short period of time. Since the purification of seawater requires both energy and increased investment and maintenance costs, today water electrolysis is often not economically feasible in regions with no fresh water access.This marks the starting point of this PhD project. The primary goal of this thesis is the development and demonstration of a catalyst suitable for direct electrolysis of seawater to hydrogen and oxygen, without the formation of Cl2.Nickel based layered double hydroxides (Ni-LDH) and oxyhydroxides (Ni-OOH), particularly when doped with other transition metals, have shown very high catalytic activity with respect to the OER. If sufficient current densities under practical conditions (1A/cm2, < 80 °C, stable for several thousand hours) below the thermodynamic onset potential of the ClER of around 1.7 V could be reached, an active suppression of the ClER is not necessarily needed.Initially, we investigate potential highly active mixed-metal LDH catalysts for the OER in sea water splitting, which are synthesized by a particularly simple, quick and efficient procedure proposed by Li et al. in 2020. Based on their work, we conduct a screening study of 36 unique compounds derived from abundantly available transition metals (Ni, Fe, Mn, Cr, Co, Cu, Zn, Al). The LDHs are coated onto a Ni foam substrate by a two-step dip coating process from metal nitrate solutions. In a first approach, we only consider compounds consisting of two transition metals with equal molar ratios. We then investigate their catalytic activity as well as the long term stability for up to 1000 hours in industrially relevant (60 – 80°C, 6M KOH) fresh water and sea water conditions, particularly regarding catalyst poisoning effects of the sea water constituents on the catalyst.We then give an outlook on the next step in the project, which will be to make use of the simple synthesis procedure by implementing it into an autonomous lab robot setup. The robot platform will comprise all steps of the experiment from synthesis over electrochemical testing, data analysis and machine learning based optimization. This way, we will showcase the potential of combining high-throughput screening with AI-assisted materials discovery. As a proof-of-concept, the robot will reproduce the initial screening study that was carried out manually. Subsequently, autonomous data analysis and synthesis optimization functionality will be implemented and the robot will run several iterations of closed-loop catalyst optimization experiments without human interaction.