The Restructuring-Induced CoO_x Catalyst for Electrochemical Water Splitting

Abstract

Restructuring is an important yet less understood phenomenon in the catalysis community. Recent studies have shown that a group of transition metal sulfide catalysts can completely or partially restructure during electrochemical reactions which then exhibit high activity even better than the best commercial standards. However, such restructuring processes and the final structures of the new catalysts are elusive, mainly due to the difficulty from the reaction-induced changes that cannot be captured by ex situ characterizations. To establish the true structure–property relationship in these in situ generated catalysts, we use multimodel operando characterizations including Raman spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity to investigate the restructuring of a representative catalyst, Co 9 S 8 , that shows better activity compared to the commercial standard RuO 2 during the oxygen evolution reaction (OER), a key half reaction in water-splitting for hydrogen generation. We find that Co 9 S 8 ultimately converts to oxide cluster (CoO x ) containing six oxygen coordinated Co octahedra as the basic unit which is the true catalytic center to promote high OER activity. The density functional theory calculations verify the in situ generated CoO x consisting of edge-sharing CoO 6 octahedral clusters as the actual active sites. Our results also provide insights to design other transition-metal-based materials as efficient electrocatalysts that experience a similar restructuring in OER.

Atomically dispersed single Ni site catalysts for high-efficiency CO2 electroreduction at industrial-level current densities

“…23 A similar change of the Ni oxidation state can be inferred for Ni–N–C, although this needs to be elucidated with the in situ XAS data. 44,54 Overall, the catalytic performance reported in this study represents one of the best performances of Ni–N–C catalysts so far, reaching an impressive 61.1 mA cm −2 at a minimal overpotential of 490 mV (Table S6, ESI†).…”

Phase Segregation in Cobalt Iron Oxide Nanowires toward Enhanced Oxygen Evolution Reaction Activity

“…In addition, the band corresponding to the rock-salt structure is weakly observed after 1.1 V vs RHE potential bias. Taking into account that Raman spectroscopy is a bulk sensitive technique and the high stability of spinel and oxyhydroxide phases in this potential range at pH 14 and 25 °C (based on Pourbaix diagram), , the rock-salt phase transformation appears to occur not only on the surface but also in the bulk region. This will be further elaborated in the XRD section below.…”

Operando Identification of Active Species and Intermediates on Sulfide Interfaced by Fe3O4 for Ultrastable Alkaline Oxygen Evolution at Large Current Density

“…However, there are only a few reports , that suggest the inevitable surface reconstruction on transition-metal chalcogenides during the alkaline OER process. The complicated surface reconstruction process at the atomic level remains poorly understood and true catalytically active species are controversial so far due to the limitations of characterization techniques under realistic operando conditions.…”