The low overpotential regime of acidic water oxidation part I: the importance of O₂ detection

Abstract

The high overpotential required for the oxygen evolution reaction (OER) represents a significant barrier for the production of closed-cycle renewable fuels and chemicals. Ruthenium dioxide is among the most active...

The low overpotential regime of acidic water oxidation part II: trends in metal and oxygen stability numbers

“…3a . Two timespans are used for the integral values: one for the ramp-up and first ∼2 minutes of electrolysis, during which capacitive charging makes up a significant portion of the current; 35 and the other for the remainder of the electrolysis in steady-state. Taking into account that the Ru dissolution commences with the onset of applied current, the ramp-up to 0.5 mA cm −2 geo (∼1.4 V RHE ) was found to have more than 100 Ru atoms dissolved per labelled oxygen in the evolved O 2 (6500 pmol cm −2 geo dissolved Ru compared to 60 pmol cm −2 geo labelled OER), in contrast to the reduced dissolution rate of ∼40 Ru atoms dissolved per labelled oxygen atom evolved during steady state electrolysis (27 000 pmol cm −2 geo dissolved Ru compared to 680 pmol cm −2 geo labelled OER).…”

“…The labelled oxygen evolved during 30 minutes of electrolysis was ∼2% of a monolayer, using the capacitive charging current to determine the surface area, whereas the ruthenium dissolution approximately corresponded to one monolayer. In the first article of this series, 35 we showed that ruthenium oxides sputter-deposited at a series of temperatures ranging from 25 °C to 400 °C had widely varying activity on a geometric basis, but that activity converges when normalizing by capacitive charging current, motivating capacitive charging current as a measure of the electrochemically active surface area (ECSA) on these catalysts. To determine the number of moles in a monolayer equivalent, we further use a specific capacitance of 115 μF cm −2 geo from ref.…”

“…To determine the number of moles in a monolayer equivalent, we further use a specific capacitance of 115 μF cm −2 geo from ref. 35 and an active site density of 5 nm −2 , which is the density of coordinatively unsaturated sites on RuO 2 (110). The fact that the amount of labelled oxygen evolution is much lower than a monolayer equivalent implies that it is likely limited to oxygen atoms at the surface of the catalyst, such as bridging oxygen atoms.…”

“…3a. Two timespans are used for the integral values: one for the ramp-up and first B2 minutes of electrolysis, during which capacitive charging makes up a significant portion of the current; 35 and the other for the remainder of the electrolysis in steady-state. Taking into account that the Ru dissolution geo .…”

“…– Ru 18 O x /Ru-foam formed by oxidation of ruthenium foam (see the first article of this series 35 ) in 97% H 2 18 O electrolyte…”