HER Properties Research Articles

Fabrication of a 3D self-supporting Ni–P/Ni2P/CC composite and its robust hydrogen evolution reaction properties in alkaline solution

The Ni–P/Ni2P/CC composite exhibits excellent alkaline HER properties derived from Ni–P filling the sites on the CC not occupied by Ni2P nanosheets.

Improving Electrochemical Hydrogen Evolution of Ag@CN Nanocomposites by Synergistic Effects with α-Rich Proteins.

A graphitic carbon nitride nanostructure has been successfully functionalized by incorporation of different silver contents and subsequent modification with an α-rich protein, namely hemoglobin. Mechanochemistry has been employed, as an efficient and sustainable procedure, for the incorporation of the protein. A complete characterization analysis has been performed following a multitechnique approach. Particularly, XPS data exhibited considerable differences in the C 1s region for the Hb/xAg@CN, ensuring the successful protein anchorage on the surface of the graphitic carbon nitride-based materials. The as-synthesized nanomaterials delivered impressive performance toward hydrogen evolution reactions with an overpotential of 79 mV at a current density of 10 mA/cm2 for Hb/20Ag@CN nanohybrids, which is comparable with the most efficient HER electrocatalysts reported in the literature. The outstanding HER properties were associated with the unique synergistic interactions, quantitatively measured, between AgNPs, Hb tertiary architecture, and the graphitic carbon nitride networks.

Atomically Dispersed Pt on Screw-like Pd/Au Core-shell Nanowires for Enhanced Electrocatalysis.

Engineering noble metal nanostructures at the atomic level can significantly optimize their electrocatalytic performance and remarkably reduce their usage. We report the synthesis of atomically dispersed Pt on screw-like Pd/Au nanowires by using ultrafine Pd nanowires as seeds. Au can selectively grow on the surface of Pd nanowires by an island growth pattern to fabricate surface defect sites to load atomically dispersed Pt, which can be confirmed by X-ray absorption fine structure measurements and aberration corrected HRTEM images. The nanowires with 2.74 at % Pt exhibit superior HER properties in acidic solution with an overpotential of 20.6 mV at 10 mA cm-2 and enhanced alkaline ORR performance with a mass activity over 15 times greater than the commercial platinum/carbon (Pt/C) catalysts.

Amorphous (Fe)Ni-MOF-derived hollow (bi)metal/oxide@N-graphene polyhedron as effectively bifunctional catalysts in overall alkaline water splitting

The unique hollow nanostructures (Ni1-xFex-HP) were fabricated by the template-engaged pyrolysis from amorphous (bi)metal-organic-frameworks with tunable polyhedron-like morphology by various Fe content. Ni1-xFex-HP features as hollow polyhedron with mesoporous wall, consisting of dominant metal/alloy coupled with a small fraction of their oxides and few-layer N-graphene shell (FLNG). Thanks for the structural and compositional feature to strengthen the synergism of Ni, NiO and N-graphene on HER, as well as FeNi alloy, NiFe oxide, and N-graphene on OER, the optimal Ni-HP and Ni0.5Fe0.5-HP octahedron present good bifunctional properties for HER (overpotential of 215 mV to reach 10 mA cm−2, Tafel slope of 133 mV dec−1) and OER (overpotential of 280 mV to reach 10 mA cm−2, Tafel slope of 79 mV dec−1) on glass carbon electrode in 1.0 M alkaline solution. Moreover, the electrocatalytic performance can be further enhanced by directly coating on nickel foam (NF), where the overpotentials of Ni-HP/NF and Ni0.5Fe0.5-HP/NF is only 98 and 220 mV at current density of 10 mA cm−2 for HER and OER, respectively. The integrated asymmetrical two-electrode configuration (Ni0.5Fe0.5-HP/NF||Ni-HP/NF) displays low cell voltage of 1.57 V to reach 10 mA cm−2, accompanying with strong durability for overall alkaline water splitting. This work opens up an effectively time-saving strategy using aMOFs with well-defined structure instead of highly crystalline metal-organic frameworks (cMOFs) as precursor to design hollow and nanostructured hybrids for energy conversion.

Enhancing catalytic activity of tungsten disulfide through topology

Phase transition through local strain engineering is an exciting yet complex phenomenon in nanoscience for enhancing electronic, magnetic, and catalytic properties of nanomaterials. Here we report a topotactic transformation in 2H-WS2 nanobelts into 1T-WS2 nanohelices, which is mediated via an aqueous electrochemical activation method. The resulting nanohelices exhibited superior catalytic properties for HER with a low overpotential of 170 mV for an electrocatalytic current density of 10 mA/cm2. Notably, the electrochemical stability of WS2 nanohelices increased after 20,000 cycles, where the stability of the Pt benchmark catalyst is known to decrease, thus implying WS2 nanohelices as ideal catalysts for long-term electrochemical processes. The emergence of such enhanced properties is attributed to the strain induced decrease in charge transfer resistance, enhanced per site activity and increased number of active edge sites in 1T-WS2 nanohelices. This study points the way for creating topological motifs in 2D materials with novel properties.

Exposure of active edge structure for electrochemical H2 evolution from VS2/MWCNTs hybrid catalysts

Developing highly efficient and stable non-noble-metal catalysts for electrochemical hydrogen production is the main subject toward energy conversion systems. In this work, the vanadium disulfide/multi-walled carbon nanotubes (VS2/MWCNTs) is synthesized by a facile hydrothermal process. The introducing of MWCNTs could provide abundant sites for the anchoring of VS2 to expose more edge structure. Besides, the electron transfer from MWCNTs to VS2 could increase the electron density of VS2 and further enhance the HER performance of the composites. The optimized VS2/MWCNTs composite exhibits excellent HER properties with a small η10 of 123 mV and low Tafel slope of 40 mV dec−1. Meanwhile, the cobwebby network of the hybrid could significantly improve the electron transfer and durability of the catalyst. This work provides an available route for further application of the transition metal dichalcogenides based nanostructure.

Fabricating a novel three component nano-electrocatalyst, Co5.57Fe1.62Ni1.81S8/rGO, and its application toward electrochemical hydrogen evolution reaction

Co5.57Fe1.62Ni1.81S8 nanocomposite hybridized with reduced graphene oxide (Co5.57Fe1.62Ni1.81S8/rGO) was prepared through a one-step hydrothermal method. The hybrid was characterized by XRD, EDX, FESEM and HRTEM. The electrochemical hydrogen evolution behavior of nanohybrids with different mass ratios was studied as modified glassy carbon electrodes by linear sweep voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The results showed overpotential in 10 mA/cm2 (−100 mV) for Co5.57Fe1.62Ni1.81S8/rGO (1 g:0.5 g) among all nanohybrids. Also, the obtained Tafel slope (53.6 mV/dec) confirmed the Volmer-Heyrovsky mechanism for HER. The electro-catalytic properties for HER of Co5.57Fe1.62Ni1.81S8/rGO (1 g:0.5 g) were compared with some transition metal dichalcogenide based composites.

Surface Confinement Etching and Polarization Matter: A New Approach To Prepare Ultrathin PtAgCo Nanosheets for Hydrogen-Evolution Reactions

One of the important objectives in fuel-cell technology is to improve the activity and reduce the loading of Pt for hydrogen-evolution electrocatalysis. Here, an oxidative etching strategy of stacking faults is developed to prepare PtAgCo nanosheets by element-specific anisotropic growth. Sophisticated use of defects in crystal growth allows tailoring the morphology and interfacial polarization to improve catalytic performance of nanosheets for the hydrogen-evolution reaction. Systematic studies reveal that the presence of the stacking faults may be the knob for the formation of nanosheets. In particular, the chemical composition of nanosheets is potentially the key for altering the hydrogen-evolution reaction. As a result, the PtAgCo-II ultrathin nanosheets possess useful HER properties, achieving a current density up to 705 mA cm–2 at a potential of −400 mV.

Core–shell and alloy integrating PdAu bimetallic nanoplates on reduced graphene oxide for efficient and stable hydrogen evolution catalysts

PdAu nanoplates with different core–shell structures on rGO were generated by manipulating the competition between galvanic replacement and chemical reduction with the alloy and core–shell integrating nanoplates exhibiting superior HER properties.

Modification of Electrodeposited Co-Pd Alloy Catalysts By Superimposed High Magnetic Field

Palladium and its alloys have been a subject of interest in many research centers all over the world. Due to the price and accessibility of Pd, intensive tests are conducted aiming to invent alloys with catalytic properties similar to those of platinum, but much cheaper than palladium itself. Alloys of Co-Pd, Pd-Fe, Pd-Ni and Pd-Cr exhibit high catalytic activity for the four electron oxygen reduction reaction.The properties of Co-Pd alloys for the hydrogen evolution reaction are close to the properties of pure platinum. This makes it possible to use them, for example, in fuel cells. Tests performed so far have demonstrated that the Pd-Co alloys are characterized by much better electrocatalytic properties for HER than pure palladium. Application of an external magnetic field during the deposition of an alloy causes an additional convection at the electrode surface through the magnetohydrodynamic effect (MHD), paramagnetic force and magnetic field gradient force. This additional convection results in changes of the alloy composition, structure and morphology, and these, in turn, affect the further properties as magnetic as catalytical of the produced alloys. Magnetic field applied parallel to the surface of the electrode generates convection (magnetohydrodynamic effect MHD) of the electrolyte; it results in a laminar flow on the surface of the electrode which reduces the diffusion layer and increases the concentrations gradients. This results in change of the size of the grains and thus can also influence the texture and formation of various phases of the deposits. These various effects can be caused at the same time by the above mentioned convection but also by the magnetic properties, when the field is superimposed the growth in the direction of easier magnetization appears. Optimal conditions of electrolytic deposition of cobalt matrix nanoalloys will be sought through selection of proper composition of electrolyte, changes of electrolysis parameters and by application of external electromagnetic field with intensity up to 12 Tesla. Initial experiments, when the magnetic field was limited up to 1 T, show the improvement of catalytical properties together with increase of magnetic field orientated parallel to the surface of electrode. The influence of magnetic field with higher strength on electrodeposition of alloys with catalytical properties is needed to be clarified. Acknowledgement This work was supported by Polish National Science Center under grants 011/01/N/ST5/05509 and 2013/09/B/ST8/00211. This work was also supported by Polish Ministry of Science and Higher Education under grant IP2012/001072.