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A hurdle to the commercialization of thermoelectrochemical cells (TECs) based on the redox reaction of hexacyanoferrate (HCF) to convert low-grade waste heat into electricity is the high manufacturing cost resulting from the noble electrode materials like Pt and nanostructured carbon. Herein, we report the successful exploitation of low-cost Cu, which has not been considered ever for the TEC electrode material because of its heavy corrosion in the operating condition. Interestingly, we found that by precisely tuning the pH of the electrolyte-containing HCF to the immunity window, Cu was applicable to a TEC electrode, showing a performance closely equal to Pt and superior to carbon materials with negligible corrosion. Cu-based TECs can achieve a commercially viable module cost of $0.19 W −1 , which far exceeds the general cost target for thermoelectric devices (∼$1 W −1 ) and is even more competitive than that for commercial solar power (∼$0.4 W −1 ).

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Growing the hydrogen economy requires improving the stability, efficiency, and economic value of water-splitting technology, which uses an intermittent power supply from renewable energy sources. Alkaline water electrolysis systems face a daunting challenge in terms of stabilizing hydrogen production under the condition of transient start-up/shut-down operation. Herein, we present a simple but effective solution for the electrode degradation problem induced by the reverse-current under transient power condition based on a fundamental understanding of the degradation mechanism of nickel (Ni). It was clearly demonstrated that the Ni cathode was irreversibly oxidized to either the β-Ni(OH) 2 or NiO phases by the reverse-current flow after shut-down, resulting in severe electrode degradation. It was also determined that the potential of the Ni electrode should be maintained below 0.6 V RHE under the transient condition to keep a reversible nickel phase and an activity for the hydrogen evolution reaction. We suggest a cathodic protection approach in which the potential of the Ni electrode is maintained below 0.6 V RHE by the dissolution of a sacrificial metal to satisfy the above requirement; irreversible oxidization of the cathode is prevented by connecting a sacrificial anode to the Ni cathode. In the accelerated durability test under a simulated reverse-current condition, lead was found to be the most promising candidate for the sacrificial metal, as it is cost effective and demonstrates chemical stability in the alkaline media. A newly defined metric, a reverse-current stability factor, highlights that our system for protecting the cathode against the reverse-current is an efficient strategy for stable and cost effective alkaline hydrogen production.

No abstract