(296e) Electrochemical Approach for Hydrogen Storage in LOHC

Green-hydrogen is a promising candidate to address the pressing need of sustainable fuels. However, the intrinsically low mass-density (0.089 g/L) at ambient conditions makes its storage/transportation extremely challenging. Nowadays, hydrogen is mostly stored either as high-pressure-gas in cylinders/canisters or liquid in cryogenic tanks, both of which incur high containment costs, safety concerns, and boil-off loss.

Hydrogen storage in liquid-organic-hydrogen-carriers (LOHC) exhibits numerous advantages over the conventional compression/liquefaction technologies. Particularly, it can leverage the existing infrastructures for fossil fuels which are established in regards of both safety and cost. Besides, there are a handful of LOHC candidates that can fulfil the practical target of hydrogen-storage capacity, ≥6 wt% of entire systems including containers and valves. There are two steps for storing hydrogen in LOHC: an exothermic hydrogenation step followed by an endothermic dehydrogenation step. Recently, LOHC systems with significantly reduced dehydrogenation temperature of ~200 °C have been demonstrated, providing opportunities for the practical implementation of LOHC-based hydrogen storage. In contrast, the hydrogenation step, which also require relatively high temperature, but more importantly high H₂ pressure, remains a challenge due to the significant while inevitable entropy loss (gas to liquid). Here, we propose to tackle this challenge by direct hydrogenation of LOHC under ambient conditions electrochemically without phase transformation, using H₂O as the source of proton and electron, eliminating the safety concern posed by H₂-gas. Using a membrane electrode assembly-based reactor, and toluene as an example, we demonstrate the feasibility of this electrochemical approach for H₂ storage. Specifically, we achieve encouragingly high current efficiency (>95%) for the desired process of Toluene-Methylcyclohexane conversion, at industrial relevant current density. Furthermore, based on the preliminary data collected, we conducted comprehensive Life-cycle-assessment and Technoeconomic analysis to identify the technological gaps for the implementation of this technology.