Abstract
The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation. Applying a reversible multifunctional electrocatalyst to the hydrogen electrode is a practical solution. Ir exhibits excellent catalytic activity for hydrogen evolution reactions (HER), and hydrogen oxidation reactions (HOR), yet irreversibly converts to amorphous IrOx at potentials > 0.8 V/RHE, which is an excellent catalyst for oxygen evolution reactions (OER), yet a poor HER and HOR catalyst. Harnessing the multifunctional catalytic characteristics of Ir, here we design a unique Ir-based electrocatalyst with high crystallinity for OER, HER, and HOR. Under OER operation, the crystalline nanoparticle generates an atomically-thin IrOx layer, which reversibly transforms into a metallic Ir at more cathodic potentials, restoring high activity for HER and HOR. Our analysis reveals that a metallic Ir subsurface under thin IrOx layer can act as a catalytic substrate for the reduction of Ir ions, creating reversibility. Our work not only uncovers fundamental, uniquely reversible catalytic properties of nanoparticle catalysts, but also offers insights into nanocatalyst design.
Highlights
The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation
A recent study proposed reducing the damage to the electrode by selectively promoting hydrogen oxidation reactions (HOR) catalysts by suppressing the ORR10 and introducing a water oxidation catalyst to the anode of the polymer electrolyte membrane (PEM) fuel cell to induce an oxygen evolution reactions (OER), as it is a reaction that competes with the carbon corrosion reaction[9]
We explored the mechanism of the reversible IrNiOx layer of IrNi/C-HT using electrochemical flowcell coupling operando inductively coupled plasma-mass spectrometry (ICP-MS)
Summary
The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation. A recent study proposed reducing the damage to the electrode by selectively promoting HOR catalysts by suppressing the ORR10 and introducing a water oxidation catalyst to the anode of the PEM fuel cell to induce an OER, as it is a reaction that competes with the carbon corrosion reaction[9] In this regard, multifunctional catalysts can be a promising strategy in environments where the electrochemical reaction changes rapidly, such as the voltage reversal of water electrolysis and PEM fuel cell systems. Fuel starvation in PEM fuel cells or voltage reversal in water electrolysis occurs, and irreversible oxidation of Ir-based catalyst would happen at the anode in the fuel cell and at the cathode in water electrolyzers, resulting in the loss of multifunctional catalytic properties. The prepared catalysts were applied to the fuel starvation of the PEM fuel cell and the reverse voltage of the water electrolyzer to confirm their viability in a real environment
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