High gravimetric energy density, earth-abundance, and environmental friendliness of hydrogen sources have inspired the utilization of hydrogen fuel as a clean alternative to fossil fuels. Hydrogen evolution reaction ...High gravimetric energy density, earth-abundance, and environmental friendliness of hydrogen sources have inspired the utilization of hydrogen fuel as a clean alternative to fossil fuels. Hydrogen evolution reaction （HER）, a half reaction of water splitting, is crucial to the low-cost production of pure H2 fuels but necessitates the use of electrocatalysts to expedite reaction kinetics. Owing to the availability of low-cost oxygen evolution reaction （OER） catalysts for the counter electrode in alkaline media and the lack of low-cost OER catalysts in acidic media, researchers have focused on developing HER catalysts in alkaline media with high activity and stability. Nickel is well-known as an HER catalyst and continuous efforts have been undertaken to improve Ni-based catalysts as alkaline electrolyzers： In this review, we summarize earlier studies of HER activity and mechanism on Ni surfaces, along with recent progress in the optimization of the Ni-based catalysts using various modern techniques. Recently developed Ni-based HER catalysts are categorized according to their chemical nature, and the advantages as well as limitations of each category are discussed. Among all Ni-based catalysts, Ni-based alloys and Ni-based hetero-structure exhibit the most promising electrocatalytic activity and stability owing to the fine-tuning of their surface adsorption properties via a synergistic nearby element or domain. Finally, selected applications of the developed Ni-based HER catalysts are highlighted, such as water splitting, the chloralkali process, and microbial electrolysis cell.展开更多
The development of facile strategies to tune the oxygen vacancy （OV） content in transition metal oxides （TMOs） is paramount to obtain low-cost and stable electrocatalysts, but still highly challenging. Taking NiC0...The development of facile strategies to tune the oxygen vacancy （OV） content in transition metal oxides （TMOs） is paramount to obtain low-cost and stable electrocatalysts, but still highly challenging. Taking NiC0204 as a model system, we have experimentally established a facile calcination and electrochemical activation （EA） methodology to dramatically increase the concentration of OVs and provide theoretical insight into how the concentration of OVs affects the performance of spinel TMOs towards the electrochemical hydrogen evolution reaction （HER）. A self-supported cathode of OV-rich NiC0204 nanowire arrays was found to exhibit higher HER activity and better stability in alkaline media than its counterparts with fewer OVs. The electrocatalytic HER activity was in good agreement with the increasing concentration of OVs in the studied samples. A large current density of 360 mA.cm-2 was reached with an overpotential of only 317 mV. Additionally, such a facile strategy was able to efficiently generate OVs in other TMOs （e.g., CoFe204 and NiFe204） for enhanced HER performance. In addition, our theoretical results suggest that the increasing OV concentration reduces the adsorption energy of water molecules and their dissociation energy barrier on the surface of the catalyst, thus leading to performance improvement of spinel TMOs toward the electrochemical HER. This work may open a new avenue to increase the concentration of OVs in TMOs in a controlled manner for promising applications in a variety of fields.展开更多
We report a three-dimensional hierarchical ternary hybrid composite of molybdenum disulfide （MoS2）, reduced graphene oxide （GO）, and carbon nano- tubes （CNTs） prepared by a two-step process. Firstly, reduced GO-...We report a three-dimensional hierarchical ternary hybrid composite of molybdenum disulfide （MoS2）, reduced graphene oxide （GO）, and carbon nano- tubes （CNTs） prepared by a two-step process. Firstly, reduced GO-CNT composites with three-dimensional microstructuresare synthesized by hydrothermal treatment of an aqueous dispersion of GO and CNTs to form a composite structure via π-π interactions. Then, MoS2 nanoparticles are hydrothermally grown on the surfaces of the GO-CNT composite. This ternary composite shows superior electrocatalytic activity and stability in the hydrogen evolution reaction, with a low onset potential of only 35 mV, a Tafel slope of -38 mV.decade-1 and an apparent exchange current density of 74.25 mA.cm-2. The superior hydrogen evolution activity stemmed from the synergistic effect of MoS2 with its electrocatalytically active edge-sites and excellent electrical coupling to the underlying graphene and CNT network.展开更多
The development of highly active and cost-effective hydrogen evolution reaction （HER） catalysts is of vital importance to addressing global energy issues. Here, a three-dimensional interconnected porous carbon nanof...The development of highly active and cost-effective hydrogen evolution reaction （HER） catalysts is of vital importance to addressing global energy issues. Here, a three-dimensional interconnected porous carbon nanofiber （PCNF） membrane has been developed and utilized as a support for active cobalt phosphide （COP） nanoparticles. This rationally designed self-supported HER catalyst has a lotus root-like multichannel structure, which provides several intrinsic advantages over conventional CNFs. The longitudinal channels can store the electrolyte and ensure fast ion and mass transport within the catalysts. Additionally, mesopores on the outer and inner carbon walls enhance ion and mass migration of the electrolyte to HER active CoP nanoparticles, thus shortening the ion transport distance and increasing the contact area between the electrolyte and the CoP nanoparticles. Moreover, the conductive carbon substrate provides fast electron transfer pathways by forming an integrated conductive network, which further ensures fast HER kinetics. As a result, the CoP/PCNF composites exhibit low onset-potentials （-20, -91, and -84 mV in 0.5 M H2SO4, 1 M PBS, and 1 M KOH, respectively）. These findings show that CoP/PCNF composites are promising self-supporting and high-performance all-pH range HER catalysts.展开更多
Hydrogen evolution by electrocatalysis clean energy. However, it is challenging is an attractive method of supplying to find cheap and efficient alternatives to rare and expensive platinum based catalysts. Pt provides...Hydrogen evolution by electrocatalysis clean energy. However, it is challenging is an attractive method of supplying to find cheap and efficient alternatives to rare and expensive platinum based catalysts. Pt provides the best hydrogen evolution performance, because it optimally balances the free energies of adsorption and desorption. Appropriate control of these quantities is essential for producing an efficient electrocatalyst. We demonstrate, based on first principles calculations, a stepwise designed Rh-Au-Si ternary catalyst, in which adsorption （the Volmer reaction） and desorption （the Heyrovsky reaction） take place on Rh and Si surfaces, respectively. The intermediate Au surface plays a vital role by promoting hydrogen diffusion from the Rh to the Si surface. Theoretical predictions have been explored extensively and verified by experimental observations. The optimized catalyst （Rh-Au-SiNW-2） has a com- position of 2.2：28.5：69.3 （Rh：Au：Si mass ratio） and exhibits a Tafel slope of 24.0 mV.dec-L Its electrocatalytic activity surpasses that of a commercial 40 wt.% Pt/C catalyst at overpotentials above 0.19 V by exhibiting a current density of greater than 108 mA-cm-2. At 0.3 V overpotential, the turnover frequency of Rh-Au-SiNW-2 is 10.8 times greater than that of 40 wt.% Pt/C. These properties may open new directions in the stepwise design of highly efficient catalysts for the hydrogen evolution reaction （HER）.展开更多
Chemical vapor deposition has been the most-promising approach for growing large-area high-quality graphene films on planar substrates. Beyond the lateral growth, the synthesis of three-dimensional （3D） graphene has...Chemical vapor deposition has been the most-promising approach for growing large-area high-quality graphene films on planar substrates. Beyond the lateral growth, the synthesis of three-dimensional （3D） graphene has also been demon- strated recently on metal foams and insulating nanoparticles for exploring their applications in electrochemical electrodes. However, the existing approaches need either to prefabricate abundant starting substrates, or to construct porous frameworks for graphene growth. Herein, we report a straightforward, bioinspired strategy for growing large-quantity graphene flakes on cuttlebone substrates using the chemical vapor deposition （CVD） method. The separated graphene flakes from growth substrates are highly crystalline and layer-thickness controllable, outperforming the traditional chemically exfoliated graphene with few surface groups. Due to their inheriting the biomineral-derived morphology, the 3D graphene microstructures show a highly exposed and curved surface, which can load more MoSx（x ≥ 2） catalysts than other planar supports for highly efficient hydrogen generation. Briefly, the bioinspired approach is expected to achieve a reasonable balance between quality and quantity for graphene production, thus propelling its wide applications in energy storage and conversion devices.展开更多
The development of new non-precious metal catalysts and understanding the origin of their activity for the hydrogen evolution reaction （HER） are essential for rationally designing highly active low-cost catalysts as...The development of new non-precious metal catalysts and understanding the origin of their activity for the hydrogen evolution reaction （HER） are essential for rationally designing highly active low-cost catalysts as alternatives to state-of-the-art precious metal catalysts. Herein, manganese oxide/hydroxide was demonstrated as a highly active electrocatalysts for the HER by fabricating MnO2 nanosheets coated with Cu2O nanowire arrays （Cu2O@MnO2 NW@NS） on Cu foam followed by an in situ chronopotentiometry （CP） treatment. It was discovered that the in situ transformation of Cu2O@MnO2 into Cu@Mn（OH）2 NW@NS by the CP treatment drastically boosted the catalytic activity for the HER due to an enhancement of its intrinsic activity. Together with the benefits from such （3D） core-sheU arrays for exposing more accessible active sites and efficient mass and electron transfers, the resulting Cu@Mn（OH）2 NW@NS exhibited excellent HER activity and outstanding durability in terms of a low overpotential of 132 mV vs. RHE at 10 mA/cm2, Overall, we expect these findings to generate new opportunities for the exploration of other Mn-based nanomaterials as efficient electrocatalysts and enable further understanding of their catalytic processes.展开更多
文摘High gravimetric energy density, earth-abundance, and environmental friendliness of hydrogen sources have inspired the utilization of hydrogen fuel as a clean alternative to fossil fuels. Hydrogen evolution reaction （HER）, a half reaction of water splitting, is crucial to the low-cost production of pure H2 fuels but necessitates the use of electrocatalysts to expedite reaction kinetics. Owing to the availability of low-cost oxygen evolution reaction （OER） catalysts for the counter electrode in alkaline media and the lack of low-cost OER catalysts in acidic media, researchers have focused on developing HER catalysts in alkaline media with high activity and stability. Nickel is well-known as an HER catalyst and continuous efforts have been undertaken to improve Ni-based catalysts as alkaline electrolyzers： In this review, we summarize earlier studies of HER activity and mechanism on Ni surfaces, along with recent progress in the optimization of the Ni-based catalysts using various modern techniques. Recently developed Ni-based HER catalysts are categorized according to their chemical nature, and the advantages as well as limitations of each category are discussed. Among all Ni-based catalysts, Ni-based alloys and Ni-based hetero-structure exhibit the most promising electrocatalytic activity and stability owing to the fine-tuning of their surface adsorption properties via a synergistic nearby element or domain. Finally, selected applications of the developed Ni-based HER catalysts are highlighted, such as water splitting, the chloralkali process, and microbial electrolysis cell.
文摘The development of facile strategies to tune the oxygen vacancy （OV） content in transition metal oxides （TMOs） is paramount to obtain low-cost and stable electrocatalysts, but still highly challenging. Taking NiC0204 as a model system, we have experimentally established a facile calcination and electrochemical activation （EA） methodology to dramatically increase the concentration of OVs and provide theoretical insight into how the concentration of OVs affects the performance of spinel TMOs towards the electrochemical hydrogen evolution reaction （HER）. A self-supported cathode of OV-rich NiC0204 nanowire arrays was found to exhibit higher HER activity and better stability in alkaline media than its counterparts with fewer OVs. The electrocatalytic HER activity was in good agreement with the increasing concentration of OVs in the studied samples. A large current density of 360 mA.cm-2 was reached with an overpotential of only 317 mV. Additionally, such a facile strategy was able to efficiently generate OVs in other TMOs （e.g., CoFe204 and NiFe204） for enhanced HER performance. In addition, our theoretical results suggest that the increasing OV concentration reduces the adsorption energy of water molecules and their dissociation energy barrier on the surface of the catalyst, thus leading to performance improvement of spinel TMOs toward the electrochemical HER. This work may open a new avenue to increase the concentration of OVs in TMOs in a controlled manner for promising applications in a variety of fields.
基金Majid Khan and Ammar Bin Yousaf contributed equally to this work. This work is supported by the China Scholarship Council （CSC）, and the National Natural Science Foundation of China （Nos. 11275203 and U1232128）.
文摘We report a three-dimensional hierarchical ternary hybrid composite of molybdenum disulfide （MoS2）, reduced graphene oxide （GO）, and carbon nano- tubes （CNTs） prepared by a two-step process. Firstly, reduced GO-CNT composites with three-dimensional microstructuresare synthesized by hydrothermal treatment of an aqueous dispersion of GO and CNTs to form a composite structure via π-π interactions. Then, MoS2 nanoparticles are hydrothermally grown on the surfaces of the GO-CNT composite. This ternary composite shows superior electrocatalytic activity and stability in the hydrogen evolution reaction, with a low onset potential of only 35 mV, a Tafel slope of -38 mV.decade-1 and an apparent exchange current density of 74.25 mA.cm-2. The superior hydrogen evolution activity stemmed from the synergistic effect of MoS2 with its electrocatalytically active edge-sites and excellent electrical coupling to the underlying graphene and CNT network.
基金The authors are grateful for the financial support from the National Natural Science Foundation of China （Nos. 51433001 and 51373037）, the Program of Shanghai Academic Research Leader （No. 17XD1400100）.
文摘The development of highly active and cost-effective hydrogen evolution reaction （HER） catalysts is of vital importance to addressing global energy issues. Here, a three-dimensional interconnected porous carbon nanofiber （PCNF） membrane has been developed and utilized as a support for active cobalt phosphide （COP） nanoparticles. This rationally designed self-supported HER catalyst has a lotus root-like multichannel structure, which provides several intrinsic advantages over conventional CNFs. The longitudinal channels can store the electrolyte and ensure fast ion and mass transport within the catalysts. Additionally, mesopores on the outer and inner carbon walls enhance ion and mass migration of the electrolyte to HER active CoP nanoparticles, thus shortening the ion transport distance and increasing the contact area between the electrolyte and the CoP nanoparticles. Moreover, the conductive carbon substrate provides fast electron transfer pathways by forming an integrated conductive network, which further ensures fast HER kinetics. As a result, the CoP/PCNF composites exhibit low onset-potentials （-20, -91, and -84 mV in 0.5 M H2SO4, 1 M PBS, and 1 M KOH, respectively）. These findings show that CoP/PCNF composites are promising self-supporting and high-performance all-pH range HER catalysts.
文摘Hydrogen evolution by electrocatalysis clean energy. However, it is challenging is an attractive method of supplying to find cheap and efficient alternatives to rare and expensive platinum based catalysts. Pt provides the best hydrogen evolution performance, because it optimally balances the free energies of adsorption and desorption. Appropriate control of these quantities is essential for producing an efficient electrocatalyst. We demonstrate, based on first principles calculations, a stepwise designed Rh-Au-Si ternary catalyst, in which adsorption （the Volmer reaction） and desorption （the Heyrovsky reaction） take place on Rh and Si surfaces, respectively. The intermediate Au surface plays a vital role by promoting hydrogen diffusion from the Rh to the Si surface. Theoretical predictions have been explored extensively and verified by experimental observations. The optimized catalyst （Rh-Au-SiNW-2） has a com- position of 2.2：28.5：69.3 （Rh：Au：Si mass ratio） and exhibits a Tafel slope of 24.0 mV.dec-L Its electrocatalytic activity surpasses that of a commercial 40 wt.% Pt/C catalyst at overpotentials above 0.19 V by exhibiting a current density of greater than 108 mA-cm-2. At 0.3 V overpotential, the turnover frequency of Rh-Au-SiNW-2 is 10.8 times greater than that of 40 wt.% Pt/C. These properties may open new directions in the stepwise design of highly efficient catalysts for the hydrogen evolution reaction （HER）.
基金This work was financially supported by the National Basic Research Program of China （Nos. 2013CB932603, 2012CB933404, 2012CB921404, and 2013CB934600）, the National Natural Science Foundation of China （Nos. 51432002, 51121091, 51520105003, 51290272, and 51222201）, the Ministry of Education of China （No. 20120001130010）, and the Beijing Municipal Science and Technology Planning Project （No. Z151100003315013）.
文摘Chemical vapor deposition has been the most-promising approach for growing large-area high-quality graphene films on planar substrates. Beyond the lateral growth, the synthesis of three-dimensional （3D） graphene has also been demon- strated recently on metal foams and insulating nanoparticles for exploring their applications in electrochemical electrodes. However, the existing approaches need either to prefabricate abundant starting substrates, or to construct porous frameworks for graphene growth. Herein, we report a straightforward, bioinspired strategy for growing large-quantity graphene flakes on cuttlebone substrates using the chemical vapor deposition （CVD） method. The separated graphene flakes from growth substrates are highly crystalline and layer-thickness controllable, outperforming the traditional chemically exfoliated graphene with few surface groups. Due to their inheriting the biomineral-derived morphology, the 3D graphene microstructures show a highly exposed and curved surface, which can load more MoSx（x ≥ 2） catalysts than other planar supports for highly efficient hydrogen generation. Briefly, the bioinspired approach is expected to achieve a reasonable balance between quality and quantity for graphene production, thus propelling its wide applications in energy storage and conversion devices.
基金This work was financially supported by the National Basic Research Program of China （No. 2015CB932302）, the National Key Research and Development Program of China （No. 2016YFB0101200）, the National Natural Science Foundation of China （Nos. 91645123, 21573249, 21703257 and 21773263）, and the Strategic Priority Research Program of the Chinese Academy of Sciences （No. XDB12020100）. We thank Dr. Z. J. Zhao and Prof. F. Liu at the Center for Analysis and Testing, ICCAS for their help for the XPS analysis.
文摘The development of new non-precious metal catalysts and understanding the origin of their activity for the hydrogen evolution reaction （HER） are essential for rationally designing highly active low-cost catalysts as alternatives to state-of-the-art precious metal catalysts. Herein, manganese oxide/hydroxide was demonstrated as a highly active electrocatalysts for the HER by fabricating MnO2 nanosheets coated with Cu2O nanowire arrays （Cu2O@MnO2 NW@NS） on Cu foam followed by an in situ chronopotentiometry （CP） treatment. It was discovered that the in situ transformation of Cu2O@MnO2 into Cu@Mn（OH）2 NW@NS by the CP treatment drastically boosted the catalytic activity for the HER due to an enhancement of its intrinsic activity. Together with the benefits from such （3D） core-sheU arrays for exposing more accessible active sites and efficient mass and electron transfers, the resulting Cu@Mn（OH）2 NW@NS exhibited excellent HER activity and outstanding durability in terms of a low overpotential of 132 mV vs. RHE at 10 mA/cm2, Overall, we expect these findings to generate new opportunities for the exploration of other Mn-based nanomaterials as efficient electrocatalysts and enable further understanding of their catalytic processes.
