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Abundant availability of seawater grants economic and resource‐rich benefits to water electrolysis technology requiring high‐purity water if undesired reactions such as chlorine evolution reaction (CER) competitive to oxygen evolution reaction (OER) are suppressed. Inspired by a conceptual computational work suggesting that OER is kinetically improved via a double activation within 7 Å‐gap nanochannels, RuO2 catalysts are realized to have nanoscopic channels at 7, 11, and 14 Å gap in average (dgap), and preferential activity improvement of OER over CER in seawater by using nanochanneled RuO2 is demonstrated. When the channels are developed to have 7 Å gap, the OER current is maximized with the overpotential required for triggering OER minimized. The gap value guaranteeing the highest OER activity is identical to the value expected from the computational work. The improved OER activity significantly increases the selectivity of OER over CER in seawater since the double activation by the 7 Å‐nanoconfined environments to allow an OER intermediate (*OOH) to be doubly anchored to Ru and O active sites does not work on the CER intermediate (*Cl). Successful operation of direct seawater electrolysis with improved hydrogen production is demonstrated by employing the 7 Å‐nanochanneled RuO2 as the OER electrocatalyst.

Theoretical computational studies have claimed that the catalytic activity of a family of heterogeneous catalysts (e.g., metal catalysts) is governed by a linear scaling relationship (LSR) between adsorption energy levels of intermediates on active sites of catalysts. The volcano shape of the activity versus the adsorption energy of one of the intermediates was obtained from the LSR and the Brønsted–Evans–Polanyi relationship. An improved activity can be achieved using a catalyst having optimized adsorption energy of the volcano or alternatively by circumventing or breaking the LSR. Herein, we demonstrated that the LSR of a series of transition metal terephthalates (MTPs; M = Fe, Co, Ni, Cu, or Zn) as electrocatalysts for the oxygen reduction reaction (ORR) was broken in the presence of polypyrrole (pPy) as a proton donor. The reason for the LSR breakage was that the intermediate to which the proton of pPy was delivered was different depending on the metal of MTP. Also, pPy affected the adsorption energy of the specific intermediate (the target of the proton transfer) more strongly while the other intermediates were less affected by pPy. Experimentally as well as theoretically, pPy significantly improved the ORR activity of MTPs, altering the activity volcano plot. The most significant improvement was found on CoTP: the onset potential of ORR on CoTP was shifted toward the more easy-to-be-reduced direction from 0.7 to 0.85 VRHE at 1 mA cm–2.

Electrocatalytic oxygen reduction reaction (ORR) in aqueous media proceeds along a pathway having multiple steps in which multiple surface intermediates are involved (* -> *OO -> *OOH -> *O -> *OH where * = active site of catalyst). Proton supplied from media plays a crucial role on the ORR mechanism. Therefore, pH of media affects the kinetics of ORR significantly. In the same vein, it is expected that the ORR activity is improved in the presence of proton donor (HD) around active sites of catalysts. In this presentation, we demonstrate a possibility that a series of proton donors are involved in protonation of the surface intermediates. The ORR overpotential was improved by 100 mV at pH 13 on transition metal oxide catalysts. The overpotential improvement was intensified as the pH of media decreased. It is suspected that the pH affects deprotonation of the proton donors (HD -> H+ + D-). High pH deprotonate the proton donors so that the effects of proton donors decrease. However, the proton of HD survives in acidic media so that the proton transfer from HD to active site is facilitated. The ORR overpotential gain was as large as 400 mV at pH 4 even if the oxide catalyst was not stable at the acidic pH. At pH 7, the overpotential improvement was estimated at 200 mV.