Electrochemical – Thermally-Activated Chemical (E-TAC) Water Splitting

events hall

Prof. Avner Rothschild

11.03.2021

ZOOM

14:30

In conventional water electrolysis, the water oxidation and reduction reactions are coupled in both time and space, therefore the cell must be divided into hydrogen and oxygen compartments. The Electrochemical – Thermally-Activated Chemical (E-TAC) water splitting cycle decouples these reactions by dividing the process into two stages; an electrochemical (E) stage that reduces water at the cathode and charges a nickel hydroxide anode to nickel oxyhydroxide, followed by a chemical (TAC) stage that reduces the charged anode back to its initial state by oxidizing water. This chemical reaction is accelerated at elevated temperatures (~100 deg. C), providing a handle to control the evolution of oxygen in the cell so as to avoid mixing with hydrogen. The E-TAC cycle enables overall water splitting at an average cell voltage of ~1.5 V in a membraneless cell architecture that offers potential for cost reduction by eliminating membranes and sealing components and supports high-pressure hydrogen production. High electrolytic efficiency of 98.7% is achieved by dividing the four-electron oxygen evolution reaction, with a minimum onset overpotential of 300-400 mV, into four one-electron reactions wherein four Ni(II) atoms are charged to Ni(III), followed by a chemical reaction with water that evolves oxygen spontaneously. The operational challenges that arise from swinging between the cold E and hot TAC stages and the material challenges that arise from swinging between bias and open-circuit conditions and from the finite capacity of the nickel (oxy)hydroxide anode will be presented.

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