Selectively Enhanced Electrocatalytic Oxygen Evolution within Nanoscopic Channels Fitting a Specific Reaction Intermediate for Seawater Splitting

Abstract

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.

Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl– Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal

“…For Cl – utilization in the aqueous phases, the challenge lies not only in the conflict between the kinetically favored Cl – oxidation and the thermodynamically favored H 2 O oxidation but also in the similar active sites for the intermediates in most catalysts. Though surface engineering promotes the share of the Cl – route, H 2 O oxidation is hard to avoid. − Bismuth oxychloride (BiOCl) is a typical photocatalyst of growing attention for Cl – conversion through the intrinsic microstructural evolution. − Due to the greater contribution of Cl than of O in the valence band maximum and lower electronegativity of Cl than of O, the photogenerated holes are trapped by the lattice Cl – (Cl – + h + → Cl • ) before migrating to the adsorbed H 2 O molecules. Accompanied by the release of Cl • (RCS) from the open layer structure, the resultant surface state of the BiOCl photocatalyst is “chlorine-philic”, which would drive the adsorption of ambient Cl – for recovery .…”

Electronic Reallocation in MOF-Derived Co4N–Ni3N Heterostructure Renders Chlorine-Free Overall Seawater Splitting under Large Current Density

“…These advantages include the usage of the most prevalent seawater resource on earth (∼97%) and the preservation of freshwater, which is only 1% of the earth’s water. These advantages have endowed seawater electrolysis with substantial increasing and enticing research interest. − To make the electrolysis of seawater more effortless, power efficient, and economically viable, we need to design inexpensive electrocatalysts that are generated from earth-abundant elements for speeding up the anodic OER and cathodic HER. − For the generation of hydrogen at the industrial scale, we need an electrocatalyst that can generate up to 500 mA cm –2 at low overpotentials. , Regardless, the polarization phenomenon that occurs at the electrodes and causes larger overpotentials, particularly at larger current densities, will cause the chlorine evolution reaction (ClER) to form hypochlorite (ClO – ) in natural seawater (0.5 M). This would start competing with the anodic oxygen evolution reaction, which would lead to a decrease in the effectiveness of electrolysis of seawater and fast inactivation. , In 1.0 M KOH, the theoretical potential for ClER is approximately 480 mV higher than OER.…”