Improved Hydrogen Evolution Reaction Activity Research Articles

Tuning electrochemical catalytic activity of defective 2D terrace MoSe2 heterogeneous catalyst via cobalt doping

Defective 2D terrace MoSe2/CoMoSe lateral and vertical heterostructures nanolayers electrocatalyst via metal cobalt doping displays ameliorative HER activity.

Electrodeposited hybrid Ni–P/MoSx film as efficient electrocatalyst for hydrogen evolution in alkaline media

The hybrid Ni–P/MoSx film as efficient electrocatalyst for hydrogen evolution reaction (HER) in alkaline media has been successfully synthesized through a facile two-step electrodeposition process. The obtained hybrid Ni–P/MoSx can possess the improved activity and conductivity owing to the incorporation of Ni–P. Scanning electron microscopy (SEM) shows that the edge sites of MoSx have not been completely covered by Ni–P, exposing more active sites for HER. The better dispersion of Ni–P on the surface of MoSx has been obtained, implying the enhancement of the conductivity of Ni–P/MoSx film. The electrochemical measurements confirm that Ni–P/MoSx film has the better activity for HER than pure Ni–P and MoSx, with an overpotential of 140 mV (at j = 10 mA cm−2) and a low Tafel slope of 64 mV dec−1. The improved HER activity may be attributed to the excellent conductivity of Ni–P and the synergistic effect derived from hybrid Ni–P/MoSx film.

Electronic Regulation on Mo2c Nanowires Toward Efficient Hydrogen Evolution Reaction

Advanced catalysts with element-abundance, economic-cost and stability are desired for electrochemical hydrogen evolution reaction (HER) to scale-up the promising clean energy of hydrogen.[1] Recently, early-transition metal carbides have been developed as noble-metal free electrocatalysts for HER.[2] Among them, Mo2C have received special attentions because of its varied electronic feature and catalytic performance related to the tunable phases and composition.[3] However, the negative hydrogen-binding energy (∆GH*) on Mo2C indicates a strong Mo-H, resulting in the restricted Hadsdesorption (i.e., Heyrovsky or Tafel step) and thus low HER efficiency. An optimized electron density in Mo center is highly desired. In our recent work, the effective electronic regulation on Mo2C nanowires was accomplished via constructing MoC-Mo2C heteronanowires and cobalt doping, leading to the significantly improved HER activity in both acidic and basic electrolytes.[4~6] On one hand, MoC-Mo2C heteronanowires composed of well-defined nanoparticles were accomplished via the controlled carbonization of tailored MoOx-amine precursors, which showed the reduced electronic density around Mo active centers on MoC-Mo2C interfaces. This would weaken the Mo-H for promoted Hads desorption. As expected, the optimal one consisting 31.4 wt% MoC displayed a low overpotential (η10 = 126 and 120 mV for reaching a current density of -10 mA×cm−2), a small Tafel slope (43 and 42 mV×dec−1) and a low onset overpotential (38 and 33 mV) in 0.5 M H2SO4 and 1.0 M KOH, respectively. On the other hand, an effective cobalt-doping based on Co-modified MoOx-amine precursors was developed, in which the consequently increasing electron density around E F facilitated HER kinetics. With an optimal Co/Mo ratio of 0.020, the Co-Mo2C presented a low overpotential (η 10 = 140 and 118 mV for reaching a current density of -10 mA×cm−2; η 100 = 200 and 195 mV for reaching a current density of -100 mA×cm−2), a small Tafel slope (39 and 44 mV×dec−1) and a low onset overpotential (40 and 25 mV) in 0.5 M H2SO4and 1.0 M KOH, respectively. Noticeably, the sufficient variation of electron density around E F, either the increase or decrease, can be used to optimize the hydrogen binding on metal carbides.[7] The former results in the electrons transferred into anti-bonding of Mo-H, while, the latter leads to the reduced electrons in bonding orbitals, both of which will be responsible for the weakened Mo-H and the in turn favored Hads desorption. The obviously improved HER on our MoC-Mo2C and Co-Mo2C strongly demonstrated the efficiency of above two mechanisms to optimize HER kinetics. More importantly, this work advanced the understanding of electrocatalysis on carbide surface, and opened up new opportunities to develop high-performance catalysts via rational engineering on compositions and nanostructures. Reference: [1] A. B. Laursen, S. Kegnaes, S. Dahl, I. Chorkendorff, Energy Environ. Sci., 2012, 5, 5577. [2] C. G. Morales-Guio, L. Stern and X. L. Hu, Chem. Soc. Rev., 2014, 43, 6555. [3] L. Liao, S. Wang, J. Xiao, X. Bian, Y. Zhang, M. D. Scanlon, X. Hu, Y. Tang, B. Liu, H. H. Girault, Energy Environ. Sci., 2014, 7, 387. [4] H. L. Lin, Z. P. Shi, S. N. He, X. Yu, S. N. Wang, Q. S. Gao, Y. Tang, Chem. Sci. 2016, DOI: 10.1039/c6sc00077k. [5] H. L. Lin, N. Liu, Z. P. Shi, Y. L. Guo, Y. Tang, Q. S. Gao, Adv. Funct. Mater., 2016, DOI: 10.1002/adfm.201600915. [6] Z. P. Shi, Y. X. Wang, H. L. Lin, H. B. Zhang, M. K. Shen, S. H. Xie, Y. H. Zhang, Q. S. Gao, Y. Tang, J. Mater. Chem. A 2016, DOI: 10.1039/c6ta01900e. [7] Q. S. Gao, N. Liu, S. N. Wang, Y. Tang, Nanoscale, 2014, 6, 14106. Fig. 1 (a) j 0 (obtained by extrapolating Tafel curves to η= 0 mV) and j 150 (current density at η= 150 mV) of the MoC-Mo2C heteronanowires, which are associated with the ratio of surface Mo3+/Mo2+ determined by XPS analysis. (b) Schematic illustration for the HER activity relying on the electron density of Mo in a series of MoCx electrocatalysts. Figure 1

Structure–function relationship of electrodeposited MoSx film in N, N-dimethyl-formamide/H2O mixture solvent as electrocatalyst for hydrogen evolution

Nanostructured plate-like island molybdenum sulfides (MoSx) film has been synthesized successfully through a facile one-step electrodeposition method from the mixture solution of N, N-dimethyl-formamide (DMF) and H2O. The effect of different ratio of DMF to H2O on the MoSx film has been investigated. Scanning electron microscopy (SEM) shows that when the ratio of DMF to H2O is 1:20, the as-prepared MoSx film exhibits maximum island structures, exposing most edges and rims. The electrochemical measurements confirm that MoSx film deposited in the mixed solution of VDMF: VH2O = 1:20 has the best hydrogen evolution reaction (HER) activity, with an overpotential of 80 mV. The improved HER activity may be attributed to the polarity difference of DMF-H2O and morphology directing of DMF. Therefore, using DMF–H2O mixture solution with the appropriate ratio may be a facile and effective way to prepare the excellent electrocatalysts for HER.

A vertical-oriented WS2 nanosheet sensitized by graphene: an advanced electrocatalyst for hydrogen evolution reaction.

Electrocatalytic hydrogen production at low overpotential is a promising route towards a clean and sustainable energy. Layered transition metal dichalcogenides (LTMDs) have attracted copious attention for their outstanding activities in hydrogen evolution reaction (HER). However, the horizontally laid nanosheets suffer from a paucity of active edge sites. Herein, we report the successful synthesis of vertical-oriented WS2 nanosheets through a hydrothermal method followed by a facile sulfurization process. Furthermore, the surface of synthesized WS2 nanosheets was decorated by ultrathin reduced graphene oxide (rGO) nanoplates. This is achieved for the first time by bringing the rGO on the surface of vertical-oriented WS2 nanosheets, which is conducive to rapid electron transport during the HER process. Significantly, the as-synthesized rGO/WS2 nanosheets exhibit improved HER activity as compared to the undecorated ones. It needs a low overpotential of only 229 mV vs. RHE to afford a current density of 10 mA cm(-2). We believe that this hybrid structure demonstrated remarkable HER activity brought about by a compatible synergism between rGO and WS2.

Role of pendant proton relays and proton-coupled electron transfer on the hydrogen evolution reaction by nickel hangman porphyrins.

The hangman motif provides mechanistic insights into the role of pendant proton relays in governing proton-coupled electron transfer (PCET) involved in the hydrogen evolution reaction (HER). We now show improved HER activity of Ni compared with Co hangman porphyrins. Cyclic voltammogram data and simulations, together with computational studies using density functional theory, implicate a shift in electrokinetic zone between Co and Ni hangman porphyrins due to a change in the PCET mechanism. Unlike the Co hangman porphyrin, the Ni hangman porphyrin does not require reduction to the formally metal(0) species before protonation by weak acids in acetonitrile. We conclude that protonation likely occurs at the Ni(I) state followed by reduction, in a stepwise proton transfer-electron transfer pathway. Spectroelectrochemical and computational studies reveal that upon reduction of the Ni(II) compound, the first electron is transferred to a metal-based orbital, whereas the second electron is transferred to a molecular orbital on the porphyrin ring.

Molybdenum disulfide/pyrolytic carbon hybrid electrodes for scalable hydrogen evolution.

The electrochemical generation of hydrogen fuel via the proton reduction in the Hydrogen Evolution Reaction (HER) in aqueous media is currently dependent on the use expensive noble metal catalysts for which alternatives must be sought. Molybdenum disulfide (MoS₂) has shown great promise as a suitable electrocatalyst in this regard. While many lab-scale experiments on the HER activity of this material have demonstrated its viability and explored some fundamental mechanistic features of HER at MoS₂, these experimental techniques are often ill-suited to large scale production of such electrodes. In this study we present work on the fabrication of MoS₂/pyrolytic carbon (PyC) electrodes via vapour phase sulfurization of Mo thin films. These hybrid electrodes combine the catalytic activity of MoS₂ with the conductivity and stability of PyC, whilst using industrially compatible processing techniques. Structural defects in the sulfur lattice were found to be key catalytically active sites for HER and thinner MoS₂ films displayed a higher quantity of these defects and, hence, an improved HER activity. The observed Tafel slope of 95 mV decade(-1) is comparable to previous literature works on MoS₂ HER performance.

Size‐Dependent Enhancement of Electrocatalytic Oxygen‐Reduction and Hydrogen‐Evolution Performance of MoS2 Particles

MoS2 particles with different size distributions were prepared by simple ultrasonication of bulk MoS2 followed by gradient centrifugation. Relative to the inert microscale MoS2, nanoscale MoS2 showed significantly improved catalytic activity toward the oxygen-reduction reaction (ORR) and hydrogen-evolution reaction (HER). The decrease in particle size was accompanied by an increase in catalytic activity. Particles with a size of around 2 nm exhibited the best dual ORR and HER performance with a four-electron ORR process and an HER onset potential of -0.16 V versus the standard hydrogen electrode (SHE). This is the first investigation on the size-dependent effect of the ORR activity of MoS2, and a four-electron transfer route was found. The exposed abundant Mo edges of the MoS2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges. This newly discovered process provides a simple protocol to produce inexpensive highly active MoS2 catalysts that could easily be scaled up. Hence, it opens up possibilities for wide applications of MoS2 nanoparticles in the fields of energy conversion and storage.

Hydrogen evolution on nano-particulate transition metal sulfides

The hydrogen evolution reaction (HER) on carbon supported MoS2 nanoparticles is investigated and compared to findings with previously published work on Au(111) supported MoS2. An investigation into MoS2 oxidation is presented and used to quantify the surface concentration of MoS2. Other metal sulfides with morphologies similar to MoS2 such as WS2, cobalt-promoted WS2, and cobalt-promoted MoS2 were also investigated in the search for improved HER activity. Experimental findings are compared to density functional theory (DFT) calculated values for the hydrogen binding energies (deltaGH) on each system.

Exploiting synergy between FCC and feed pretreating units to improve refinery margins and produce low-sulfur fuels

The development of high performance bi-functional electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with low cost materials has remained a great challenge in electrochemical water splitting. Herein, we design and develop novel Co-doped Fe0.95S1.05 nanoplates, which were synthesized using Fe(CO)5 as precursor for the first time via a one pot reaction. Fe0.9Co0.05S1.05 lead to enhanced OER activity with a low overpotential of ∼ 0.27 V at 20 mA/cm2, small Tafel slope of ∼ 46 mV/decade, as well as improved HER activity with a Tafel slope of 114 mV/decade and a current density of 20 mA/cm2 at an overpotential of ∼ 0.385 V. This study produced the most active pyrrhotite FeS based catalyst for electrochemical water splitting, which suggests a scalable, low cost, simple, and highly efficient catalyst for water splitting.