Experimental realization of 2D boridene electrocatalysts for anion-exchange membrane water electrolyzers

Sustainable hydrogen (H2) generation by a potentially zero-carbon method like water electrolysis is crucial to our decarbonization strategies. The incumbent water electrolyzer technologies have already been used to demonstrate H2 production at the gigawatts scale. However, the next big transition to the terawatt scale demands new breakthroughs in electrolyzer components, especially related to the electrodes that forms one of the most crucial parts of the whole device. Anion-exchange membrane water electrolyzers (AEMWEs) are tipped to be the successor technology for green hydrogen generation but there are very few electrocatalysts with established performances at conditions relevant to commercial AEMWEs. Furthermore, there is a fundamental gap in the understanding of electrode behavior at such extreme conditions. Project Borocat fills these gaps by delivering a novel set of highly efficient and stable electrocatalysts and establishing the science needed to understand their true catalytic and degradation behavior under relevant conditions. Boridenes are two-dimensional (2D) boron analogues of graphene with tunable surface functionalities for different catalytic applications. Their predicted excellent activities, combined with their lower cost and earth abundance makes them one of the most promising classes of electrocatalysts for electrocatalytic water splitting. However, their experimental realization has been a challenge and will be addressed within the scope of this project. To demonstrate the industrial relevance of such promising electrocatalysts, it is essential to probe their activities at larger current densities (> 1 A/cm2) and longer timescales (> 1000 h). The conventional electrochemical measurements involving a 3-electrode setup (including a rotating-disc electrode) introduces mass transport limitations originating due to several factors (such as low solubility of product gases, formation of microbubbles, etc.), severely constraining the catalyst evaluation at higher current densities. Moreover, the conventional 3-electrode systems do not resemble the true environment that a catalyst experiences in the membrane electrode assemblies (MEAs) of an AEMWE. Furthermore, the degradation behavior of electrodes at such extreme conditions bears useful information that may guide the development of mitigation measures to prevent degradation, but such investigations are rarely undertaken. Under Project Borocat, we will not only fabricate 2D boridenes but also evaluate them at 1 A/cm2 for ~1000 h and perform detailed degradation assessment, thus overcoming the said challenges. Owing to our team’s expertise, we will develop a generalized synthesis protocol based on molten salt route to fabricate 2D boridene phases of Mo, Fe, Cr and W. The optimized catalyst phases will be evaluated at ~1 A/cm2 using a gas diffusion electrode (GDE) setup. The GDE setup offers a reasonable resemblance to the MEA environment and it improves the mass transport properties due to its unique design. It also enables the possibility to perform long-term electrochemical measurements (~1000 h) to gauge a catalysts true stability profile. For degradation assessment of the electrocatalysts optimized under the GDE setup, a modified floating electrode (MFE), as developed by our team, will be employed in conjunction with identical location transmission electron microscopy (IL-TEM). This unique combination will allow us to reach GDE-like testing conditions and directly investigate the electrode under a TEM, with a possibility to track the reaction-induced changes at the same sample location. Furthermore, the electrode dissolution studies will be enabled by in-situ and ex-situ inductively coupled plasma mass spectrometry (ICP-MS) measurements. Thus, by the end of project Borocat, we will comprehensively establish substantial scientific proof in support of 2D boridenes as a notable alternative for direct incorporation in commercial AEMWE systems.