Abstract
Developing efficient and low-cost electrocatalysts for oxygen evolution reaction is crucial in realizing practical energy systems for sustainable fuel production and energy storage from ...renewable energy sources. However, the inherent linear scaling relation for most catalytic materials imposes a theoretical overpotential ceiling, limiting the development of efficient electrocatalysts. Herein, using modeled Na
x
Mn
3
O
7
materials, we report an effective strategy to construct better oxygen evolution electrocatalyst through tuning both lattice oxygen reactivity and scaling relation via alkali metal ion mediation. Specifically, the number of Na
+
is linked with lattice oxygen reactivity, which is determined by the number of oxygen hole in oxygen lone-pair states formed by native Mn vacancies, governing the barrier symmetry between O–H bond cleavage and O–O bond formation. On the other hand, the presence of Na
+
could have specific noncovalent interaction with pendant oxygen in *OOH to overcome the limitation from linear scaling relation, reducing the overpotential ceiling. Combining in situ spectroscopy-based characterization with first-principles calculations, we demonstrate that an intermediate level of Na
+
mediation (NaMn
3
O
7
) exhibits the optimum oxygen evolution activity. This work provides a new rational recipe to develop highly efficient catalyst towards water oxidation or other oxidative reactions through tuning lattice oxygen reactivity and scaling relation.
Exploring robust catalysts for water oxidation in acidic electrolyte is challenging due to the limited material choice. Iridium (Ir) is the only active element with a high resistance to the acid ...corrosion during water electrolysis. However, Ir is rare, and its large-scale application could only be possible if the intrinsic activity of Ir could be greatly enhanced. Here, a pseudo-cubic SrCo
Ir
O
perovskite, containing corner-shared IrO6 octahedrons, is designed. The Ir in the SrCo
Ir
O
catalyst shows an extremely high intrinsic activity as reflected from its high turnover frequency, which is more than two orders of magnitude higher than that of IrO
. During the electrochemical cycling, a surface reconstruction, with Sr and Co leaching, over SrCo
Ir
O
occurs. Such reconstructed surface region, likely contains a high amount of structural domains with corner-shared and under-coordinated IrO
octahedrons, is responsible for the observed high activity.
The oxygen evolution reaction (OER) is an important half reaction in many energy conversion and storage techniques. However, the development of a low‐cost easy‐prepared OER electrocatalyst with high ...mass activity and rapid kinetics is still challenging. Herein, we report the facile deposition of tannin‐NiFe (TANF) complex film on carbon fiber paper (CP) as a highly efficient OER electrocatalyst. TANF gives rapid OER reaction kinetics with a very small Tafel slope of 28 mV dec−1. The mass activity of TANF reaches 9.17×103 Ag−1 at an overpotential of 300 mV, which is nearly 200‐times larger than that of NiFe double layered hydroxide. Furthermore, tannic acid in TANF can be electrochemically extracted under anodic potential, leaving the inorganic composite NixFe1−xOyHz as the OER‐active species. This work may provide a guide to probing the electrochemical transformation and investigating the reactive species of other metal–organic complexes as heterogeneous electrocatalysts.
Get it down on paper: A tannin‐NiFe complex (TANF) ultrathin film is deposited on carbon fiber paper by coordinating tannin with Ni and Fe ions to give an efficient oxygen evolution reaction (OER) electrocatalyst with high mass activity and rapid kinetics. The inorganic species NixFe1−xOyHz is shown to be the OER‐active species.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Scanning electron microscopy, X-ray diffraction, cyclic voltammetry, chronoamperometry, in situ Raman spectroscopy, and X-ray absorption near-edge structure spectroscopy (XANES) were used to ...investigate the electrochemical oxygen evolution reaction (OER) on Cu, Cu2O, Cu(OH)2, and CuO catalysts. Aqueous 0.1 M KOH was used as the electrolyte. All four catalysts were oxidized or converted to CuO and Cu(OH)2 during a slow anodic sweep of cyclic voltammetry and exhibited similar activities for the OER. A Raman peak at 603 cm–1 appeared for all the four samples at OER-relevant potentials, ≥1.62 V vs RHE. This peak was identified as the Cu–O stretching vibration band of a CuIII oxide, a metastable species whose existence is dependent on the applied potential. Since this frequency matches well with that from a NaCuIIIO2 standard, we suggest that the chemical composition of the CuIII oxide is CuO2 –-like. The four catalysts, in stark contrast, did not oxidize the same way during direct chronoamperometry measurements at 1.7 V vs RHE. CuIII oxide was observed only on the CuO and Cu(OH)2 electrodes. Interestingly, these two electrodes catalyzed the OER ∼10 times more efficiently than the Cu and Cu2O catalysts. By correlating the intensity of the Raman band of CuIII oxide and the extent of the OER activity, we propose that CuIII species provides catalytically active sites for the electrochemical water oxidation. The formation of CuIII oxides on CuO films during OER was also corroborated by in situ XANES measurements of the Cu K-edge. The catalytic role of CuIII oxide in the O2 evolution reaction is proposed and discussed.
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In this work, a one‐pot solution method for direct synthesis of interconnected ultrafine amorphous NiFe‐layered double hydroxide (NiFe‐LDH) (<5 nm) and nanocarbon using the molecular precursor of ...metal and carbon sources is presented for the first time. During the solvothermal synthesis of NiFe‐LDH, the organic ligand decomposes and transforms to amorphous carbon with graphitic nanodomains by catalytic effect of Fe. The confined growth of both NiFe‐LDH and carbon in one single sheet results in fully integrated amorphous NiFe‐LDH/C nanohybrid, allowing the harness of the high intrinsic activity of NiFe‐LDH due to (i) amorphous and distorted LDH structure, (ii) enhanced active surface area, and (iii) strong coupling between the active phase and carbon. As such, the resultant NiFe‐LDH/C exhibits superior activity and stability. Different from postdeposition or electrostatic self‐assembly process for the formation of LDH/C composite, this method offers one new opportunity to fabricate high‐performance oxygen evolution reaction and possibly other catalysts.
A one‐pot solution method for direct synthesis of interconnected NiFe‐layered double hydroxide (NiFe‐LDH) (<5 nm) and nanocarbon using molecular precursors is presented. The confined growth of NiFe‐LDH and carbon in one single sheet results in fully integrated amorphous NiFe‐LDH/C nanohybrid with superior activity and durability for oxygen evolution reaction.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Achieving a functional and durable non-platinum group metal-based methanol oxidation catalyst is critical for a cost-effective direct methanol fuel cell. While Ni(OH)
2
has been widely ...studied as methanol oxidation catalyst, the initial process of oxidizing Ni(OH)
2
to NiOOH requires a high potential of 1.35 V vs. RHE. Such potential would be impractical since the theoretical potential of the cathodic oxygen reduction reaction is at 1.23 V. Here we show that a four-coordinated nickel atom is able to form charge-transfer orbitals through delocalization of electrons near the Fermi energy level. As such, our previously reported periodically arranged four-six-coordinated nickel hydroxide nanoribbon structure (NR-Ni(OH)
2
) is able to show remarkable methanol oxidation activity with an onset potential of 0.55 V vs. RHE and suggests the operability in direct methanol fuel cell configuration. Thus, this strategy offers a gateway towards the development of high performance and durable non-platinum direct methanol fuel cell.
Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H2 evolution performance, is a great challenge. Noble‐metal‐free catalysts ...containing Co(Fe)NC moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H2 evolution. Herein, a new photocatalyst containing g‐C3N4 decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ−)Co(δ+)N(δ−) surface bonding states lead to much superior H2 evolution activity (96.2 µmol h−1) compared to noble metal (Pt)‐decorated g‐C3N4 photocatalyst (32.3 µmol h−1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C3N4. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H2 evolution.
The unique P(δ−)Co(δ+)N(δ−) surface bonding states are constructed by decorating crystalline CoP nanodots on the g‐C3N4 nanosheet, which results in a superior H2 evolution rate of 96.2 µmol h−1 with the highest quantum efficiency value of 12.4% at 420 nm.
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Electrocatalysts based on hierarchically structured and heteroatom‐doped non‐noble metal oxide materials are of great importance for efficient and low‐cost electrochemical water splitting systems. ...Herein, the synthesis of a series of hierarchical hollow nanoplates (NPs) composed of ultrathin Co3O4 nanosheets doped with 13 different metal atoms is reported. The synthesis involves a cooperative etching−coordination−reorganization approach starting from zeolitic imidazolate framework‐67 (ZIF‐67) NPs. First, metal atom decorated ZIF‐67 NPs with unique cross‐channels are formed through a Lewis acid etching and metal species coordination process. Afterward, the composite NPs are converted to hollow Co3O4 hierarchical NPs composed of ultrathin nanosheets through a solvothermal reaction, during which the guest metal species is doped into the octahedral sites of Co3O4. Density functional theory calculations suggest that doping of small amount of Fe atoms near the surface of Co3O4 can greatly enhance the electrocatalytic activity toward the oxygen evolution reaction (OER). Benefiting from the structural and compositional advantages, the obtained Fe‐doped Co3O4 hierarchical NPs manifest superior electrocatalytic performance for OER with an overpotential of 262 mV at 10 mA cm−2, a Tafel slope of 43 mV dec−1, and excellent stability even at a high current density of 100 mA cm−2 for 50 h.
Metal‐atom‐doped Co3O4 hierarchical nanoplates constructed by ultrathin nanosheets are synthesized by a cooperative etching−coordination−reorganization approach. The method allows doping of 13 metal elements in total. With its structural and compositional advantages, as an example, the Fe‐doped Co3O4 hierarchical nanoplates exhibit greatly enhanced electrocatalytic performance for oxygen evolution.
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Electrochemical conversion of CO2 into valued products is one of the most important issues but remains a great challenge in chemistry. Herein, we report a novel synthetic approach involving prolonged ...thermal pyrolysis of hemin and melamine molecules on graphene for the fabrication of a robust and efficient single‐iron‐atom electrocatalyst for electrochemical CO2 reduction. The single‐atom catalyst exhibits high Faradaic efficiency (ca. 97.0 %) for CO production at a low overpotential of 0.35 V, outperforming all Fe‐N‐C‐based catalysts. The remarkable performance for CO2‐to‐CO conversion can be attributed to the presence of highly efficient singly dispersed FeN5 active sites supported on N‐doped graphene with an additional axial ligand coordinated to FeN4. DFT calculations revealed that the axial pyrrolic nitrogen ligand of the FeN5 site further depletes the electron density of Fe 3d orbitals and thus reduces the Fe–CO π back‐donation, thus enabling the rapid desorption of CO and high selectivity for CO production.
High five! Prolonged thermal pyrolysis of hemin (H) and melamine (M) on graphene (G) provided a robust single‐iron‐atom electrocatalyst for CO2 reduction. The single‐atom catalyst exhibited high Faradaic efficiency (ca. 97 %) for CO production at low overpotential (0.35 V) owing to the presence of highly efficient dispersed FeN5 active sites supported on N‐doped graphene through an additional axial ligand coordinated to FeN4 (see picture; Fe red, N blue).
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LaCoO3 is an active, stable catalyst in alkaline solution for oxygen evolution reaction (OER). With lower cost, it is a potential alternative to precious metal oxides like IrO2 and RuO2 in water ...electrolysis. However, room still remains for improving its activity according to recent understandings of OER on perovskite oxides. In this work, Fe substitution has been introduced in LaCoO3 to boost its OER performance. Density function theory (DFT) calculation verified that the enhanced performance originates from the enhanced Co 3d-O 2p covalency with 10 at% Fe substitution in LaCoO3. Both DFT calculations and Superconducting Quantum Design (SQUID) magnetometer (MPMS-XL) showed a Co3+ spin state transition from generally low spin state (LS: t2g 6 eg 0, S = 0) to a higher spin state with the effect of 10 at% Fe substitution. X-ray absorption near-edge structure (XANES) supports DFT calculations on an insulator to half-metal transition with 10 at% Fe substitution, induced by spin state transition. The half-metallic LaCo0.9Fe0.1O3 possesses increased overlap between Co 3d and O 2p states, which results in enhanced covalency and promoted OER performance. This finding enlightens a new way of tuning the metal–oxygen covalency in oxide catalysts for OER.
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