Role of LiCoO<sub>2</sub> Surface Terminations in Oxygen Reduction and Evolution Kinetics

Han, Binghong; Qian, Danna; Risch, Marcel; Chen, Hailong; Chi, Miaofang; Meng, Ying Shirley; Shao‐Horn, Yang

doi:10.1021/acs.jpclett.5b00332

Cited by 66 publications

(68 citation statements)

References 31 publications

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“…It can be seen that MnCo 2 O 4 spinels locate at the left branch of the OER volcano plot, which confirms our previous explanation on the linear dependence in Figure b. This theory also explains the recent observation on Li 2 Co 2 O 4 ,[7c,34] where the switch in spin state from Co 3+ (

{normalt}_{2 g}^{6} {normale}_{normalg}^{0}

, low spin) to Co 3+ (

{normalt}_{2 g}^{6 - x} {normale}_{normalg}^{x}

, x ≈ 1, intermediate spin) at the octahedral site gives drastically enhanced ORR/OER activity. Note that our principle is different from the e g theory in perovskites, where there is only one geometric site.…”

supporting

confidence: 90%

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Wei

Feng

Scherer³

et al. 2017

Advanced Materials

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635

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Exploring efficient and low-cost electrocatalysts for the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) is critical for developing renewable energy technologies such as fuel cells, metal-air batteries, and water electrolyzers. A rational design of a catalyst can be guided by identifying descriptors that determine its activity. Here, a descriptor study on the ORR/OER of spinel oxides is presented. With a series of MnCo O , the Mn in octahedral sites is identified as an active site. This finding is then applied to successfully explain the ORR/OER activities of other transition-metal spinels, including Mn Co O (x = 2, 2.5, 3), Li Mn O (x = 0.7, 1), XCo O (X = Co, Ni, Zn), and XFe O (X = Mn, Co, Ni). A general principle is concluded that the e occupancy of the active cation in the octahedral site is the activity descriptor for the ORR/OER of spinels, consolidating the role of electron orbital filling in metal oxide catalysis.

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{normalt}_{2 g}^{6} {normale}_{normalg}^{0}

, low spin) to Co 3+ (

{normalt}_{2 g}^{6 - x} {normale}_{normalg}^{x}

supporting

confidence: 90%

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Wei

Feng

Scherer³

et al. 2017

Advanced Materials

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635

621

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“…Analogously, a very recent study on LiCoO 2 for electrochemical water oxidation and oxygen reduction also revealed the impact of charge transfer processes on the catalytic activity. 16b, 32 The water oxidation activity of various catalyst types, such as perovskites and lithium battery materials, was generally perceived to be strongly influenced by their surface states. However, recent studies also showed that the activities of two representative materials may still be different, regardless of the formation of virtually identical Co-Pi layers on their surface under electrochemical water oxidation conditions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Correlations among Structure, Electronic Properties, and Photochemical Water Oxidation: A Case Study on Lithium Cobalt Oxides

et al. 2015

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Construction of {M 4 O 4 } motifs is an effective design paradigm for molecular polyoxometalate-and oxidebased water oxidation catalysts (WOCs). However, the mechanisms beneath this bioinspired design strategy remain a topic of intense debate. The two modifications of LiCoO 2 with spinel-type and layer structures are exceptionally versatile model systems to explore the correlations among structure, electronic properties, and photochemical water oxidation. The electronic properties of both LiCoO 2 modifications are tunable through delithiation while the basic structural frameworks are maintained. This provides a unique opportunity to assign the respective influence of structures and electronic properties on the water oxidation properties. While spinel-type LiCoO 2 with {Co 4 O 4 } cubane motifs is active for photochemical water oxidation, the layered modification without cuboidal structural elements is nearly inactive. Here, we demonstrate that the water oxidation performance of both modifications can be significantly improved through chemical delithiation. A wide range of analytical methods were applied to investigate the transition of electronic properties upon delithiation, and a direct correlation between enhanced hole mobility and improved water oxidation activity was established. The difference in water oxidation activities between the two structural modifications was further linked to the role of {Co 4 O 4 } cubane motifs in constructing 3D Co−O−Co networks with expanded hole transfer paths. Thus, the promoting effects of both delithiation and {Co 4 O 4 } cubane motifs on water oxidation can be consistently explained by enhanced hole mobility.Conversion of solar energy into chemical fuels by artificial photosynthesis could provide a sustainable and flexible solution to current energy and climate problems. 1 To date, one of the most demanding steps toward solar water splitting remains the development of efficient and economic water oxidation catalysts (WOCs). 2 Even after decades of synthetic and mechanistic studies, the complex multistep processes of water oxidation with heterogeneous catalysts are not completely understood. 3 Mechanistic insight requires highly sophisticated in situ techniques which are currently being developed. 4 In a search for general WOC design concepts, cuboidal {M 4 O 4 } motifs (M = Co, Mn) inspired by the {CaMn 4 O 5 } oxygen evolving cluster (OEC) in photosystem II 5 have been established as an effective design paradigm 6 for molecular-, 7 oxide-, 8 and polyoxometalate-based 9 WOCs. Nevertheless, the precise impact of {M 4 O 4 } cubane motifs on the oxygen evolution performance remains a topic of extensive debate, 10 with the amorphous Co-Pi electrocatalysts 11 as a typical example. The absence of long-range order renders structure− activity relations of amorphous Co-Pi type WOCs rather difficult to clarify, 12 so that the precise mechanistic role of the proposed {Co 4 O 4 } building blocks remains under investigation. 13 While many water oxidation active oxides, such as Co 3 O...

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“…[9,[70][71][72] The studied catalysts Ni MOF and NiO WCP in this article are associated with a q* value of 1156 and 875 mC cm À2 mg À1 respectively. E 1 and E 2 are the range of scanned voltage used for the measurement of q*.…”

Section: Physical and Chemical Characterizationsmentioning

confidence: 99%

An Insight on the Electrocatalytic Mechanistic Study of Pristine Ni MOF (BTC) in Alkaline Medium for Enhanced OER and UOR

et al. 2018

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Hydrogen production plays a major role in technologies for renewable energy storage. Water and urea electrolysis (WE, UE) are promising processes in this regard. The oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively, are limiting the efficiency of the overall process. As catalysts for these reactions, metal-organic frameworks (MOF) have gained increasing attention due to their combinations and co-existence of metal and organic moiety properties. Here, we investigated the catalytic behavior of Ni MOF (1,3,5-Benzenetricarboxylic acid (BTC)) towards OER and UOR in alkaline medium on carbon paper (CP) as a support. The Ni MOF exhibits 346 mV overpotential (h) at a current density of 10 mA cm À2 , 79.03 A g À1 specific-mass activity at 400 mV of h than compared to wet chemically prepared (WCP) NiO and RuO 2 for OER in 1 M KOH. Meanwhile, % 230 mV of h at 10 mA cm À2 current density with appreciable stability for 12 hours for Ni MOF in 30 % KOH was also observed. For UOR in UE, Ni MOF shows an onset potential of 1.34 V vs. RHE and 63.15 mA cm À2 current density at 1.5 V vs RHE in 1 M KOH in the presence of 1 M urea. The observed results of OER and UOR catalytic behavior are better than wet chemically prepared (WCP) NiO and noble benchmark RuO 2 catalyst under identical conditions. The results suggested that the MOF plays a major role in enhancing the catalytic activity by the facile formation of Ni(OH) 2 /NiOOH, stability and electronic properties due to their porous and interconnected structure.

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Role of LiCoO₂ Surface Terminations in Oxygen Reduction and Evolution Kinetics

Cited by 66 publications

References 31 publications

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Correlations among Structure, Electronic Properties, and Photochemical Water Oxidation: A Case Study on Lithium Cobalt Oxides

An Insight on the Electrocatalytic Mechanistic Study of Pristine Ni MOF (BTC) in Alkaline Medium for Enhanced OER and UOR

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Role of LiCoO2 Surface Terminations in Oxygen Reduction and Evolution Kinetics

Cited by 66 publications

References 31 publications

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition‐Metal Spinels

Correlations among Structure, Electronic Properties, and Photochemical Water Oxidation: A Case Study on Lithium Cobalt Oxides

An Insight on the Electrocatalytic Mechanistic Study of Pristine Ni MOF (BTC) in Alkaline Medium for Enhanced OER and UOR

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Role of LiCoO₂ Surface Terminations in Oxygen Reduction and Evolution Kinetics