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2020 Volume 41 Issue 11
2020, 41(11):
Abstract:
2020, 41(11): 1683-1691
doi: 10.1016/S1872-2067(20)63616-6
Abstract:
The development of efficient and stable non-mercury catalysts for the chlor-alkali industry is desirable but remains a great challenge. Herein, we design a series of ruthenium catalysts for acetylene hydrochlorination by regulating the electronic structure of ruthenium ions through coordination with various ligands (thiourea, phenanthroline, and L-lactic). The turnover frequencies (TOFs) and apparent activation energies for the acetylene hydrochlorination have a linear relationship with the binding energy of Ru3+ in the ruthenium catalysts. The synergetic effect of the ruthenium ion and ligands plays an important role in acetylene hydrochlorination. The Ru-Thi/AC catalyst with thiourea as the ligand shows the highest TOF and stability in acetylene hydrochlorination. The present study provides a rational method to regulate the electronic structure of supported metal catalysts with high catalytic performance exhibited by the carbon-supported heterogeneous catalysts.
The development of efficient and stable non-mercury catalysts for the chlor-alkali industry is desirable but remains a great challenge. Herein, we design a series of ruthenium catalysts for acetylene hydrochlorination by regulating the electronic structure of ruthenium ions through coordination with various ligands (thiourea, phenanthroline, and L-lactic). The turnover frequencies (TOFs) and apparent activation energies for the acetylene hydrochlorination have a linear relationship with the binding energy of Ru3+ in the ruthenium catalysts. The synergetic effect of the ruthenium ion and ligands plays an important role in acetylene hydrochlorination. The Ru-Thi/AC catalyst with thiourea as the ligand shows the highest TOF and stability in acetylene hydrochlorination. The present study provides a rational method to regulate the electronic structure of supported metal catalysts with high catalytic performance exhibited by the carbon-supported heterogeneous catalysts.
2020, 41(11): 1692-1697
doi: 10.1016/S1872-2067(20)63628-2
Abstract:
The development of efficient oxygen evolution electrocatalysts with reduced noble metal uses is a critical challenge for the deployment of various advanced energy conversion technologies. Here, a series of lanthanide-contained 6H-perovskites with a formula of Ba3LnIr2O9 (Ln=lanthanides) are investigated as oxygen evolution electrocatalysts, whose active subunits (i.e., face-sharing IrO6 dimers) can be regulated by the lanthanides in terms of catalytic activity. By using density functional theory (DFT) calculations, we establish the theoretical trend in activity for Ba3LnIr2O9 6H-perovskites, the activity of which is correlated with the difference of adsorption free energy (△GO-△GOH) between O* and OH* reaction intermediates. We further establish a volcano curve between △GO-△GOH and the calculated O p-band center. Among the Ba3LnIr2O9 6H-perovskites, Ba3LaIr2O9 locates at the peak of volcano curve, and correspondingly is the most active electrocatalyst due to the optimal O p-band property.
The development of efficient oxygen evolution electrocatalysts with reduced noble metal uses is a critical challenge for the deployment of various advanced energy conversion technologies. Here, a series of lanthanide-contained 6H-perovskites with a formula of Ba3LnIr2O9 (Ln=lanthanides) are investigated as oxygen evolution electrocatalysts, whose active subunits (i.e., face-sharing IrO6 dimers) can be regulated by the lanthanides in terms of catalytic activity. By using density functional theory (DFT) calculations, we establish the theoretical trend in activity for Ba3LnIr2O9 6H-perovskites, the activity of which is correlated with the difference of adsorption free energy (△GO-△GOH) between O* and OH* reaction intermediates. We further establish a volcano curve between △GO-△GOH and the calculated O p-band center. Among the Ba3LnIr2O9 6H-perovskites, Ba3LaIr2O9 locates at the peak of volcano curve, and correspondingly is the most active electrocatalyst due to the optimal O p-band property.
2020, 41(11): 1698-1705
doi: 10.1016/S1872-2067(20)63622-1
Abstract:
In this study, we investigated the hydrogen evolution reaction (HER) on the (101) facet of pristine and W-doped CoP using the density functional theory. Two types of Co atoms are identified on the catalyst surface:the Co atoms that present the higher d band center are marked as valid sites, whereas the others are marked as invalid sites owing to their weaker H adsorption ability. It is further revealed that W-doping can decrease the d band center of the surface Co atoms, which is beneficial for the HER; however the exposure to W weakens the desorption of H. To address the strong adsorption effect of W, the doping sites and dopant content are analyzed, and the results indicate that 8.4 wt% W doping at the invalid surface Co sites is preferred; moreover, the optimal W content increases to 16.8 wt% when W is inserted into the subsurface. The effect of W doping is weakened when the doping site is far away from the surface.
In this study, we investigated the hydrogen evolution reaction (HER) on the (101) facet of pristine and W-doped CoP using the density functional theory. Two types of Co atoms are identified on the catalyst surface:the Co atoms that present the higher d band center are marked as valid sites, whereas the others are marked as invalid sites owing to their weaker H adsorption ability. It is further revealed that W-doping can decrease the d band center of the surface Co atoms, which is beneficial for the HER; however the exposure to W weakens the desorption of H. To address the strong adsorption effect of W, the doping sites and dopant content are analyzed, and the results indicate that 8.4 wt% W doping at the invalid surface Co sites is preferred; moreover, the optimal W content increases to 16.8 wt% when W is inserted into the subsurface. The effect of W doping is weakened when the doping site is far away from the surface.
2020, 41(11): 1706-1714
doi: 10.1016/S1872-2067(20)63574-4
Abstract:
A series of Ag2-xO/FTO-i electrodes (where i denotes the current density during the electrodeposition, and i=0.5, 1, 2, 3, 4, or 7) was fabricated in 0.1 M K2B4O7 electrolyte containing Ag+ ions by galvanostatic electrocrystallization. The electrode composition and morphology were characterized using X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results reveal that the electrode films consist of Ag2O, but some of the Ag+ ions on the {111} crystal facets are oxidized into Ag2+ ions. Furthermore, the Ag2-xO/FTO-1 electrode shows a triangular slice shape of a parallel matrix with a larger exposed area of {111} crystal facets than other Ag2-xO/FTO-i (i=0.5, 2, 3, 4, or 7) electrodes. Electrocatalytic experiments prove that the Ag2-xO/FTO-1 electrode produces the highest oxidative current density, has an overpotential of 417 mV at 10 mA cm-2, and has a Tafel slope of 47 mV dec-1 in 0.1 M K2B4O7. Electrochemical impedance spectra indicate that Ag2-xO/FTO-1 electrodes have the best ability for charge transfer. In addition, in the I-t test over 10 h, the current density decreased 4%. Fortunately, both O-O and Ag2+ species were detected after electrocatalysis and a possible mechanism for the oxygen evolution reaction is proposed in which the formation of Ag2+ and O-O species on {111} facets plays a critical role.
A series of Ag2-xO/FTO-i electrodes (where i denotes the current density during the electrodeposition, and i=0.5, 1, 2, 3, 4, or 7) was fabricated in 0.1 M K2B4O7 electrolyte containing Ag+ ions by galvanostatic electrocrystallization. The electrode composition and morphology were characterized using X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results reveal that the electrode films consist of Ag2O, but some of the Ag+ ions on the {111} crystal facets are oxidized into Ag2+ ions. Furthermore, the Ag2-xO/FTO-1 electrode shows a triangular slice shape of a parallel matrix with a larger exposed area of {111} crystal facets than other Ag2-xO/FTO-i (i=0.5, 2, 3, 4, or 7) electrodes. Electrocatalytic experiments prove that the Ag2-xO/FTO-1 electrode produces the highest oxidative current density, has an overpotential of 417 mV at 10 mA cm-2, and has a Tafel slope of 47 mV dec-1 in 0.1 M K2B4O7. Electrochemical impedance spectra indicate that Ag2-xO/FTO-1 electrodes have the best ability for charge transfer. In addition, in the I-t test over 10 h, the current density decreased 4%. Fortunately, both O-O and Ag2+ species were detected after electrocatalysis and a possible mechanism for the oxygen evolution reaction is proposed in which the formation of Ag2+ and O-O species on {111} facets plays a critical role.
2020, 41(11): 1715-1722
doi: 10.1016/S1872-2067(20)63609-9
Abstract:
The high-temperature (HT) and low-temperature (LT) hydrothermal stabilities of molecular-sieve-based catalysts are important for the selective catalytic reduction of NOx with ammonia (NH3-SCR). In this paper, we report a catalyst, Cu2+ loading SAPO-17, synthesized using cyclohexylamine (CHA), which is commercially available and inexpensive and is utilized in NH3-SCR reduction for the first time. After systematic investigations on the optimization of Si and Cu2+ contents, it was concluded that Cu-SAPO-17-8.0%-0.22 displays favorable catalytic performance, even after being heated at 353 K for 24 h and at 973 K for 16 h. Moreover, the locations of CHAs, host-guest interaction and the Brönsted acid sites were explored by Rietveld refinement against powder X-ray diffraction data of as-made SAPO-17-8.0%. The refinement results showed that two CHAs exist within one eri cage and that the protonated CHA forms a hydrogen bond with O4, which indicates that the proton bonding with O4 will form the Brönsted acid site after the calcination.
The high-temperature (HT) and low-temperature (LT) hydrothermal stabilities of molecular-sieve-based catalysts are important for the selective catalytic reduction of NOx with ammonia (NH3-SCR). In this paper, we report a catalyst, Cu2+ loading SAPO-17, synthesized using cyclohexylamine (CHA), which is commercially available and inexpensive and is utilized in NH3-SCR reduction for the first time. After systematic investigations on the optimization of Si and Cu2+ contents, it was concluded that Cu-SAPO-17-8.0%-0.22 displays favorable catalytic performance, even after being heated at 353 K for 24 h and at 973 K for 16 h. Moreover, the locations of CHAs, host-guest interaction and the Brönsted acid sites were explored by Rietveld refinement against powder X-ray diffraction data of as-made SAPO-17-8.0%. The refinement results showed that two CHAs exist within one eri cage and that the protonated CHA forms a hydrogen bond with O4, which indicates that the proton bonding with O4 will form the Brönsted acid site after the calcination.
2020, 41(11): 1723-1733
doi: 10.1016/S1872-2067(20)63587-2
Abstract:
Rh(III)-catalyzed, chelation-assisted oxidative C-H imidation of arenes with N-H imide have been realized using PhI(OAc)2 as an oxidant. This transformation exhibits a broad substrate scope and tolerates various functional groups. The reaction proceeded via in situ generation of an iodine(III) imido. DFT calculations suggest that this oxidative imidaton system proceeds via a Rh(III)-Rh(V)-Rh(III) pathway.
Rh(III)-catalyzed, chelation-assisted oxidative C-H imidation of arenes with N-H imide have been realized using PhI(OAc)2 as an oxidant. This transformation exhibits a broad substrate scope and tolerates various functional groups. The reaction proceeded via in situ generation of an iodine(III) imido. DFT calculations suggest that this oxidative imidaton system proceeds via a Rh(III)-Rh(V)-Rh(III) pathway.
2020, 41(11): 1734-1744
doi: 10.1016/S1872-2067(20)63599-9
Abstract:
Sodium-treated sepiolite (NaSep)-supported transition metal catalysts (TM/NaSep; TM=Cu, Fe, Ni, Mn, and Co) were synthesized via a rotary evaporation method. Physicochemical properties of the as-synthesized samples were characterized by means of various techniques, and their catalytic activities for HCHO (0.2%) oxidation were evaluated. Among the samples, Cu/NaSep exhibited superior performance, and complete HCHO conversion was achieved at 100℃ (GHSV=240000 mL/(g·h)). Additionally, the sample retained good catalytic activity during a 42 h stability test. A number of factors, including elevated acidity, the abundance of oxygen species, and favorable low-temperature reducibility, were responsible for the excellent catalytic activity of Cu/NaSep. According to the results of the in-situ DRIFTS characterization, the HCHO oxidation mechanism was as follows:(i) HCHO was rapidly decomposed into dioxymethylene (DOM) species on the Cu/NaSep surface; (ii) DOM was then immediately converted to formate species; (iii) the resultant formate species were further oxidized to carbonates; (iv) the carbonate species were eventually converted to CO2 and H2O.
Sodium-treated sepiolite (NaSep)-supported transition metal catalysts (TM/NaSep; TM=Cu, Fe, Ni, Mn, and Co) were synthesized via a rotary evaporation method. Physicochemical properties of the as-synthesized samples were characterized by means of various techniques, and their catalytic activities for HCHO (0.2%) oxidation were evaluated. Among the samples, Cu/NaSep exhibited superior performance, and complete HCHO conversion was achieved at 100℃ (GHSV=240000 mL/(g·h)). Additionally, the sample retained good catalytic activity during a 42 h stability test. A number of factors, including elevated acidity, the abundance of oxygen species, and favorable low-temperature reducibility, were responsible for the excellent catalytic activity of Cu/NaSep. According to the results of the in-situ DRIFTS characterization, the HCHO oxidation mechanism was as follows:(i) HCHO was rapidly decomposed into dioxymethylene (DOM) species on the Cu/NaSep surface; (ii) DOM was then immediately converted to formate species; (iii) the resultant formate species were further oxidized to carbonates; (iv) the carbonate species were eventually converted to CO2 and H2O.
2020, 41(11): 1745-1753
doi: 10.1016/S1872-2067(20)63606-3
Abstract:
As the kinetically sluggish oxygen evolution reaction (OER) is considered to be a bottleneck in overall water splitting, it is necessary to develop a highly active and stable electrocatalyst to overcome this issue. Herein, we successfully fabricated a three-dimensional iron-dysprosium oxide co-regulated in-situ formed MOF-Ni arrays on carbon cloth (FeDy@MOF-Ni/CC) through a facile two-step hydrothermal method. Electrochemical studies demonstrate that the designed FeDy@MOF-Ni/CC catalyst requires an overpotential of only 251 mV to reach 10 mA cm-2 with a small Tafel slope of 52.1 mV dec-1. Additionally, the stability declined by only 5.5% after 80 h of continuous testing in 1.0 M KOH. Furthermore, a cell voltage of only 1.57 V in the overall water splitting system is sufficient to achieve 10 mA cm-2; this value is far better than that of most previously reported catalysts. The excellent catalytic performance originates from the unique 3D rhombus-like structure, as well as coupling synergies of Fe-Dy-Ni species. The combination of lanthanide and transition metal species in the synthesis strategy may open entirely new possibilities with promising potential in the design of highly active OER electrocatalysts.
As the kinetically sluggish oxygen evolution reaction (OER) is considered to be a bottleneck in overall water splitting, it is necessary to develop a highly active and stable electrocatalyst to overcome this issue. Herein, we successfully fabricated a three-dimensional iron-dysprosium oxide co-regulated in-situ formed MOF-Ni arrays on carbon cloth (FeDy@MOF-Ni/CC) through a facile two-step hydrothermal method. Electrochemical studies demonstrate that the designed FeDy@MOF-Ni/CC catalyst requires an overpotential of only 251 mV to reach 10 mA cm-2 with a small Tafel slope of 52.1 mV dec-1. Additionally, the stability declined by only 5.5% after 80 h of continuous testing in 1.0 M KOH. Furthermore, a cell voltage of only 1.57 V in the overall water splitting system is sufficient to achieve 10 mA cm-2; this value is far better than that of most previously reported catalysts. The excellent catalytic performance originates from the unique 3D rhombus-like structure, as well as coupling synergies of Fe-Dy-Ni species. The combination of lanthanide and transition metal species in the synthesis strategy may open entirely new possibilities with promising potential in the design of highly active OER electrocatalysts.
2020, 41(11): 1754-1760
doi: 10.1016/S1872-2067(20)63613-0
Abstract:
Oxygen electrocatalysis, exemplified by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is central to energy storage and conversion technologies such as fuel cells, metal-air batteries, and water electrolysis. However, highly effective and inexpensive earth-abundant materials are sought after to replace the noble metal-based electrocatalysts currently in use. Recently, metal-organic frameworks (MOFs) and carbon-based MOF derivatives have attracted considerable attention as efficient catalysts due to their exceedingly tunable morphologies, structures, compositions, and functionalization. Here, we report two-dimensional (2D) MOF/MOF derivative coupled arrays on nickel foam as binder-free bifunctional ORR/OER catalysts with enhanced electrocatalytic activity and stability. Their remarkable electrochemical properties are primarily attributed to fully exposed active sites and facilitated charge-transfer kinetics. The coupled and hierarchical nanosheet arrays produced via our growth-pyrolysis-regrowth strategy offer promise in the development of highly active electrodes for energy-related electrochemical devices.
Oxygen electrocatalysis, exemplified by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is central to energy storage and conversion technologies such as fuel cells, metal-air batteries, and water electrolysis. However, highly effective and inexpensive earth-abundant materials are sought after to replace the noble metal-based electrocatalysts currently in use. Recently, metal-organic frameworks (MOFs) and carbon-based MOF derivatives have attracted considerable attention as efficient catalysts due to their exceedingly tunable morphologies, structures, compositions, and functionalization. Here, we report two-dimensional (2D) MOF/MOF derivative coupled arrays on nickel foam as binder-free bifunctional ORR/OER catalysts with enhanced electrocatalytic activity and stability. Their remarkable electrochemical properties are primarily attributed to fully exposed active sites and facilitated charge-transfer kinetics. The coupled and hierarchical nanosheet arrays produced via our growth-pyrolysis-regrowth strategy offer promise in the development of highly active electrodes for energy-related electrochemical devices.
2020, 41(11): 1761-1771
doi: 10.1016/S1872-2067(20)63618-X
Abstract:
The establishment of multi-component catalytic systems on Fe2O3 photoanodes presents considerable potential for significantly enhancing the performance of photoelectrochemical water splitting systems. In this study, we hydrothermally synthesized a Fe2O3 photoanode. In addition, d-FeOOH synthesized via dip-coating and hydrothermally prepared h-FeOOH were used as cocatalysts and their synergistic combinations with cobalt phosphate (Co-Pi) were investigated. The synergy between h-FeOOH and Co-Pi was remarkable, whereas that between d-FeOOH and Co-Pi was negligible. For example, the onset potentials of the Co-Pi/h-FeOOH and Co-Pi/d-FeOOH dual catalysts, were cathodically shifted by 270 and 170 mV, respectively. Moreover, the photocurrent density of the Co-Pi/h-FeOOH/Fe2O3 anode was significantly higher than that of the Co-Pi/d-FeOOH/Fe2O3 one. The synergistic effect of Co-Pi and h-FeOOH could be attributed to the significantly inhibited recombination of surface charges owing to the formation of a p-n junction between β-FeOOH and Fe2O3 and the large contact area between the granular h-FeOOH and Co-Pi. However, the thin amorphous FeOOH layer of the Co-Pi/d-FeOOH/Fe2O3 anode acted as a hole-transfer medium, and weakly promoted the kinetics of the charge transfer process.
The establishment of multi-component catalytic systems on Fe2O3 photoanodes presents considerable potential for significantly enhancing the performance of photoelectrochemical water splitting systems. In this study, we hydrothermally synthesized a Fe2O3 photoanode. In addition, d-FeOOH synthesized via dip-coating and hydrothermally prepared h-FeOOH were used as cocatalysts and their synergistic combinations with cobalt phosphate (Co-Pi) were investigated. The synergy between h-FeOOH and Co-Pi was remarkable, whereas that between d-FeOOH and Co-Pi was negligible. For example, the onset potentials of the Co-Pi/h-FeOOH and Co-Pi/d-FeOOH dual catalysts, were cathodically shifted by 270 and 170 mV, respectively. Moreover, the photocurrent density of the Co-Pi/h-FeOOH/Fe2O3 anode was significantly higher than that of the Co-Pi/d-FeOOH/Fe2O3 one. The synergistic effect of Co-Pi and h-FeOOH could be attributed to the significantly inhibited recombination of surface charges owing to the formation of a p-n junction between β-FeOOH and Fe2O3 and the large contact area between the granular h-FeOOH and Co-Pi. However, the thin amorphous FeOOH layer of the Co-Pi/d-FeOOH/Fe2O3 anode acted as a hole-transfer medium, and weakly promoted the kinetics of the charge transfer process.
2020, 41(11): 1772-1781
doi: 10.1016/S1872-2067(20)63604-X
Abstract:
Silicoaluminophosphate-34 (SAPO-34) molecular sieves have important applications in the petrochemical industry as a result of their shape selectivity and suitable acidity. In this work, nanoaggregate SAPO-34 with a large external surface area was obtained by dissolving pseudoboehmite and tetraethylorthosilicate in an aqueous solution of tetraethylammonium hydroxide and subsequently adding phosphoric acid. After hydrolysis in an alkaline solution, the aluminum and silicon precursors exist as Al(OH)4- and SiO2(OH)-, respectively; this is beneficial for rapid nucleation and the formation of nanoaggregates in the following crystallization process. Additionally, to study the effect of the external surface area and pore size on the catalytic performance of different SAPO-34 structures, the alcoholysis of furfuryl alcohol to ethyl levulinate (EL) was chosen as a model reaction. In a comparison with the traditional cube-like SAPO-34, nanoaggregate SAPO-34 generated a higher yield of 74.1% of EL, whereas that with cube-like SAPO-34 was only 19.9%. Moreover, the stability was remarkably enhanced for nanoaggregate SAPO-34. The greater external surface area and larger number of external surface acid sites are helpful in improving the catalytic performance and avoiding coke deposition.
Silicoaluminophosphate-34 (SAPO-34) molecular sieves have important applications in the petrochemical industry as a result of their shape selectivity and suitable acidity. In this work, nanoaggregate SAPO-34 with a large external surface area was obtained by dissolving pseudoboehmite and tetraethylorthosilicate in an aqueous solution of tetraethylammonium hydroxide and subsequently adding phosphoric acid. After hydrolysis in an alkaline solution, the aluminum and silicon precursors exist as Al(OH)4- and SiO2(OH)-, respectively; this is beneficial for rapid nucleation and the formation of nanoaggregates in the following crystallization process. Additionally, to study the effect of the external surface area and pore size on the catalytic performance of different SAPO-34 structures, the alcoholysis of furfuryl alcohol to ethyl levulinate (EL) was chosen as a model reaction. In a comparison with the traditional cube-like SAPO-34, nanoaggregate SAPO-34 generated a higher yield of 74.1% of EL, whereas that with cube-like SAPO-34 was only 19.9%. Moreover, the stability was remarkably enhanced for nanoaggregate SAPO-34. The greater external surface area and larger number of external surface acid sites are helpful in improving the catalytic performance and avoiding coke deposition.
2020, 41(11): 1782-1789
doi: 10.1016/S1872-2067(20)63621-X
Abstract:
The most energy-inefficient step in the oxygen evolution reaction (OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co3O4 nanoparticles coupled with N-doped carbon hybrids (Ni/Co3O4@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co3O4 nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co3O4, and NC species, the obtained Ni/Co3O4@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 mV to afford 10 mA cm-2, lower Tafel slope of 52.27 mV dec-1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 mF cm-2 compared to those of unary Co3O4@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.
The most energy-inefficient step in the oxygen evolution reaction (OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co3O4 nanoparticles coupled with N-doped carbon hybrids (Ni/Co3O4@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co3O4 nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co3O4, and NC species, the obtained Ni/Co3O4@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 mV to afford 10 mA cm-2, lower Tafel slope of 52.27 mV dec-1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 mF cm-2 compared to those of unary Co3O4@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.
