Bifunctional Near‐Neutral Electrolyte Enhances Oxygen Evolution Reaction

Abstract

Performance of electrocatalytic reactions depends on not only the composition and structure of the active sites, but also their local environment, including the surrounding electrolyte. In this work, we demonstrate that BF2(OH)2− anion is the key fluoroborate species formed in the mixed KBi/KF (KBi=potassium borate) electrolyte to enhance the rate of the oxygen evolution reaction (OER) at near‐neutral pH. Through a combination of electrokinetic and in situ spectroscopic studies, we show that the mixed KBi/KF electrolyte promotes the OER via two pathways: 1) stabilizing the interfacial pH during the proton‐producing reaction with its high buffering capacity; and 2) activating the interfacial water via strong hydrogen bonds with F‐containing species. With the KBi/KF electrolyte, electrodeposited Co(OH)2 is able to achieve 100 mA/cm2 at 1.74 V, which is among the highest reported activities with earth‐abundant electrocatalysts at near neutral conditions. These findings highlight the potential of leveraging electrolyte‐engineering for improving the electrochemical performance of the OER.

High-Entropy Effect Promoting Self-Healing Behavior of Two-Dimensional Metal Oxide Electrocatalysts for Oxygen Evolution Reaction

“…Similarly, in KB i (pH = 14) with Co 2+ , FeCo also demonstrated better self-healing ability than in pure KB i (Figure S17, details in the Supporting Information), owing to supplement of Co 2+ . In KB i (pH = 14), FeCo demonstrated better self-healing ability than that in KOH, the potential increased by ∼30 mV after CV testing (see details in Figures S16, S17 and Table S4), due to pH regulation of KB i solution. , However, after CV testing, FeCo in other three solutions showed higher overpotential increase (some relative data measured in Table S4) than that in KB i solution containing Co 2+ , which is attributed to the absence of both supplement of Co 2+ and pH regulation of KB i solution. Corresponding Tafel slopes also conformed to the trend of overpotential changes (see details in Table S5).…”

“…S4), due to pH regulation of KB i solution. 52,53 However, after CV testing, FeCo in other three solutions showed higher overpotential increase (some relative data measured in Table S4) than that in KB i solution containing Co 2+ , which is attributed to the absence of both supplement of Co 2+ and pH regulation of KB i solution. Corresponding Tafel slopes also conformed to the trend of overpotential changes (see details in Table S5).…”

Understanding the effect of specific adsorption on the vibrational Stark effect of adsorbates on an electrode surface via surface enhanced spectroscopy

“…15,16 In contrast, the adsorption of weakly binding species, such as neutral organic species, is much less understood. 17,18 A key experimental challenge is the ambiguity of whether a species is specifically adsorbed, i.e. , forms a covalent bond with the surface, due to the lack of any distinct CV feature.…”

“…15,16 In contrast, the adsorption of weakly binding species, such as neutral organic species, is much less understood. 17,18 A key experimental challenge is the ambiguity of whether a species is specifically adsorbed, i.e., forms a covalent bond with the surface, due to the lack of any distinct CV feature. In situ vibrational spectroscopy techniques, e.g., surface enhanced Raman spectroscopy (SERS), 19 surface enhanced infrared absorption spectroscopy (SEIRAS) 20 and sum frequency generation (SFG), 21 are potent tools in this regard because the vibrational modes of specifically adsorbed species typically exhibit detectable shifts with potential.…”

Dynamic stabilization of nickel-based oxygen evolution electrocatalysts in the presence of chloride ions using a phosphate additive

“…For example, an additive of a fluoride anion in borate buffer is suggested to form BF 2 (OH) 2 − enhancing the OER activity of Co(OH) 2 through activating a water molecule. 25 According to the Pourbaix diagram, 26 the desired pH level for electrolysis over NiFeO x is above ca. 8.5 due to the thermodynamic limitation associated with the Ni and Fe metal dissolution.…”