Heyrovsky Step Research Articles

Experimental and computational insight into the role of cobalt and phosphorus in boosting Volmer and Heyrovsky steps of Ni in alkaline hydrogen evolution reaction

Deep insight into the role of doped hetero atoms in boosting the alkaline hydrogen evolution reaction (HER) activity is of significance for designing the low-cost electrocatalysts to produce hydrogen. Herein, we designed, synthesized, and optimized the Co and P co-doped Ni (NCP) electrocatalysts and evaluated the HER performance in alkaline medium. It was found that the NCP exhibited the enhanced hydrogen evolution performance, only need an overpotential of 57.0 mV to afford 10 mA·cm−2. The calculation results of density functional density revealed that the doped P plays an important role in modulating electron distribution of Ni and Co atoms, which reduce the Gibbs free energy of water molecule dissociation at Co sites in Volmer step, and optimize the ab/desorption of hydrogen at Ni site that bonded to P and Ni atoms in Heyrovsky step, respectively. The obtained results are conductive to understanding the electrocatalytic mechanism of alkaline HER.

Synergistic reaction kinetics of Pt single atoms/MoS2 and nanoparticles for energy-saving hydrogen production assisted by green electrosynthesis of azotetrazolate compound

Overall water splitting (OWS) involves two important half-reactions, namely hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, due to the high theoretical overpotential of OER, OWS needs to be realized with high energy consumption. Using anodic oxidation reaction with lower theoretical potential to replace oxygen evolution reaction (OER) can effectively reduce the energy consumption of overall water splitting (OWS) for hydrogen production. Here, we introduce a new oxidation reaction of green electrosynthesis of energetic materials (EMs) and coupled with OWS. The catalyst was prepared by electrodepositing Pt nanoparticles (Pt NPs) and Pt single atoms (Pt SAs) on MoS2 nanosheets, which drives highly-efficient hydrogen production of 35.6 mV to drive 10 mA cm−2. DFT calculations reveal the synergistic mechanism of Pt NPs and Pt SA/MoS2 substrate for promoting hydrogen production, is that the energy barrier of water dissociation was reduced on the Pt NC sites and the produced H* migrated to the adjacent S sites for Heyrovsky step, while the Pt SA sites served as electron regulator for more thermoneutral H* adsorption on S sites, realizing the synergistic reaction kinetics in MoS2/Pt for promoting alkaline HER. Importantly, by integrating the OWS and electrosynthesis of 5,5′-azotetrazole (ZT) EMs, the cell voltage can be significantly reduced to 1.29 V at 10 mA cm−2, realizing low-energy-consumption for hydrogen production. Meanwhile, the green electrosynthesis of ZT is achieved to avoid the hazardous process of traditional preparation methods. This study presents a new strategy for green electrosynthesis of EMs and low-energy-consumption hydrogen production.

Cobalt and sulfur co-doping induce nickel electron localization to enhance alkaline hydrogen evolution activity

Developing and synthesizing the economical electrocatalysts for alkaline hydrogen evolution reaction (HER) is essential for the large-scale production of hydrogen source. Although NiCoS-based electrocatalysts have attracted great attention, deep insight into the mechanism of boosted HER activities still needs to be further investigated, especially based on the doped Ni-based electrocatalyst. Herein, we synthesized the cobalt and sulfur co-doped nickel electrocatalysts (NCS) and the HER performance is evaluated in alkaline medium. The results show that the NCS with optimized component has a boosted HER activity compared to Ni, NiCo, and NiS, which exhibits the lower overpotential of 45.8 mV at 10 mA·cm−2 and Tafel slope of 83.4 mV·dec-1. The co-introduced Co and S are conductive to increase the reactive sites, charge transfer capacity and aerophobic property. The theoretical calculation results reveal that the doped S can induce electron localization at the Ni and Co atoms bonded to S atom. Moreover, we also confirm that the Co sites and Ni sites of NCS represent the reactive sites in the Volmer and Heyrovsky steps, respectively, and thereby boosting the hydrogen evolution activity. The obtained insights could provide a significant guideline for designing highly efficient electrocatalyst toward alkaline hydrogen evolution.

S, Fe dual doped and precisely regulated CoP porous nanoneedle arrays for efficient hydrogen evolution at 3 A cm−2

Transition metal phosphides (TMPs) have been proved as promising catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, CoP has a strong hydrogen adsorption energy, resulting in a slow Heyrovsky step in the HER. Herein, the solid phase FeS is ionized into S and Fe ions and doped into cobalt precursor during the hydrothermal process based on the precipitation dissolution equilibrium principle, and the doping strategy precisely regulated the atomic ratio of metal/P. The optimized S, Fe-CoP@IF one-dimensional porous nanoneedles structure exhibit excellent HER performance, which only required 82.3 mV and 200.1 mV to achieve 100 mA cm−2 and 3 A cm−2 together with high currents stability for 100 h. It also has better OER performance, with 260 mV reaching 100 mA cm−2. Further simulated industrial test for S, Fe-CoP@IF in alkaline anion-exchange membrane (AEM) cells show that only 1.75 V is required to attain 500 mA cm−2. Density functional theory (DFT) calculations confirmed that the dual-doping further modulates the electronic structure of CoP, reduces the Gibbs free energy for hydrogen adsorption. This work provides the possibility to further improve the catalytic activity of cobalt phosphide and apply it to industrial applications.

Synergistic Acid Hydrogen Evolution of Neighboring Pt Single Atoms and Clusters: Understanding Their Superior Activity and Mechanism.

The hydrogen evolution reaction (HER) involves two-step elementary reactions, providing an opportunity to establish dual-site synergistic catalysts. This work demonstrates carbon-supported Pt single atoms and clusters (Pt1+Cs-NPC) as an efficient catalyst for acidic HER, which exhibits an ultralow Tafel slope of 12.5 mV/dec and an overpotential of 24 mV at 10 mA/cm2 with an ultralow platinum content of 3.8 wt %. The Pt mass activity and turnover frequency (TOF) are 10.2 times and 5.4 times that of commercial Pt/C, respectively. The density functional theory (DFT) study shows that the Pt cluster regulates the electronic state structure of the adjacent Pt single atom, so that the ΔGH* at the Pt1 site approaches 0. Moreover, the DFT study confirms that Pt clusters and neighboring Pt single atoms can synergistically catalyze the Tafel step and reduce the energy barrier in forming the H-H bond. At the same time, the platinum cluster reduces the energy barrier of the nearby platinum single-atom site to the Heyrovsky step and accelerates the reaction with hydrated hydrogen ions. Studies have shown that platinum clusters and platinum single-atom composite loading structures exhibit excellent activity for the Volmer-Tafel or Volmer-Heyrovsky reaction paths of HER reactions. This work provides a clear understanding of the synergistic effect of Pt1+Cs-NPC, which provides guidance for developing efficient HER catalysts.

Electronic modulation of zinc selenide toward efficient alkaline hydrogen evolution

Effective electronic modulation is the key to fulfilling the Pt-like hydrogen evolution reaction (HER) activity on selenide-based electrocatalysts, but it also brings a huge challenge to rational structural design. Zinc selenide (ZnSe) is a potential candidate for alkaline HER. However, much fewer endeavours have been dedicated to ZnSe, hence inherent activities still need to be enhanced via facilitating the Volmer and Heyrovsky steps. Herein, we developed a simple fabrication method for copper-doped ZnSe nanoparticles embedded in nitrogen-doped carbon (namely Cu-ZnSe@NC) from bimetallic ZnCu-ZIF to promote alkaline HER. Benefitting from three-dimensional porous morphology and modulated electronic structure, the Cu-ZnSe@NC displays superior HER performance with small overpotential of 84 mV at the current density of 10 mA cm−2, comparable to that of commercial Pt/C. Experimental and theoretical results demonstrate that the incorporation of heteroatom-Cu can not only increase the number of active sites and improve the intrinsic activity of each catalytic site, but also modulate the electronic structure of the catalyst, which is advantageous to boosting H2O adsorption and optimizing the energy barrier for H adsorption for initiating the electrocatalytic pathway at alkaline electrolyte. This work provides a novel understanding for designing of selenide-based composite for HER with improved catalytic activity.

Significantly Stabilizing Hydrogen Evolution Reaction Induced by Nb-Doping Pt/Co(OH)2 Nanosheets.

High stability and efficiency of electrocatalysts are crucial for hydrogen evolution reaction (HER) toward water splitting in an alkaline media. Herein, a novel nano-Pt/Nb-doped Co(OH)2 (Pt/NbCo(OH)2 ) nanosheet is designed and synthesized using water-bath treatment and solvothermal reduction approaches. With nano-Pt uniformly anchored onto NbCo(OH)2 nanosheet, the synthesized Pt/NbCo(OH)2 shows outstanding electrocatalytic performances for alkaline HER, achieving a high stability for at least 33 h, a high mass activity of 0.65mA µg-1 Pt, and a good catalytic activity with a low overpotential of 112mV at 10mA cm-2 . Both experimental and theoretical results prove that Nb-doping significantly optimizes the hydrogen adsorption free energy to accelerate the Heyrovsky step for HER, and boosts the adsorption of H2 O, which further enhances the water activation. This study provides a new design methodology for the Nb-doped electrocatalysts in an alkaline HER field by facile and green way.

Revealing the Superior Electrocatalytic Performance of 2D Monolayer WSe2 Transition Metal Dichalcogenide for Efficient H2 Evolution Reaction

AbstractH2 evolution reaction (HER) requires an electrocatalyst to reduce the reaction barriers for the efficient production of H2. 2D transition metal dichalcogenides (2D TMDs) have emerged as a pinnacle group of materials for many potential applications, including HER. In this work, a pristine 2D monolayer WSe2 TMD is computationally designed using the first principle‐based hybrid density functional theory (DFT) to investigate its structural, electronic properties and the electrocatalytic performance for HER. The possible Volmer‐Heyrovsky and Volmer‐Tafel reaction mechanisms for HER at the W‐edge of the active site of WSe2 are studied by using a nonperiodic finite molecular cluster model W10Se21. The study shows that the pristine 2D monolayer WSe2 follows either the Volmer‐Heyrovsky or the Volmer‐Tafel reaction mechanisms with a single‐digit low reaction barrier about 6.11, 8.41 and 6.61 kcal mol−1 during the solvent phase calculations of H•‐migration, Heyrovsky and Tafel transition (TS) states, respectively. The lower reaction barriers, high turnover frequency (TOF) ≈ 4.24 × 106 s−1 and 8.86 × 107 s−1 during the Heyrovsky and Tafel reaction steps and the low Tafel slope 29.58 mV dec−1 confirm that the pristine 2D monolayer WSe2 might be a promising alternative to platinum group metals (PGM) based electrocatalyst.

Generation of dual anion vacancies on CeO2/Co4N interfaces to facilitate hydrogen evolution reaction in alkaline solution

Dual anion vacancies were introduced on the interfaces of CeO2/Co4N heterostructure by applying a mild plasma treatment, which accelerated the Volmer and Heyrovsky steps of alkaline HER performance in the water splitting process.

Novel coumarin substituted N–heterocyclic carbene Ag(I), Au(I) and Ni(II) complexes as electrocatalysts in hydrogen evolution reactions from water

An organized strategy with an analogy in controlling steric and electronic parameters of N-heterocyclic carbene (NHC) Ag (5–10), Au (11/12) and Ni (13/14) complexes as molecular electrocatalysts for engineering hydrogen evolution reaction (HER) from water is revealed. The films of 10, 13 and 14 displayed much improved activity with low overpotential −298 to −355 mV vs. RHE to drive a current density of 10 mA/cm2 (Tafel slope = 70–78 mV/dec) with exchange current density of 18–49 μA/cm2. Latter observation authenticates that the HER proceeds by the electrochemical desorption of molecular hydrogen through Volmer–Heyrovsky step. Further, the durability test suggests much lower decay rate of 11.4 and 23.1% for complexes 10 and 14 after 200 cycles, respectively. Finally, Cdl and Rct were calculated using electrochemical impedance spectroscopy. The superior activity of former complexes was manifested by the NHC design and their microcrystalline porous morphology.

Potential and support-dependent hydrogen evolution reaction activation energies on sulfur vacancies of MoS2 from GC-DFT

We present a detailed mechanistic study of HER at the sulfur vacancy VS of 2H–MoS2. We evaluate the Volmer, Tafel, and Heyrovsky transition states for the different possible reaction steps, determining the activation energy as a function of the electrochemical potential via grand-canonical density functional theory. The results show that the Volmer and Heyrovsky steps depend on the electrochemical potential and the activation energies decrease for more negative potentials, while this is not the case for the Tafel step, for which the activation energy is constant. From the activation energies at −0.2 V vs SHE, it can be concluded that during HER on VS a first hydrogen atom is adsorbed as a spectator via a Volmer step. Then, the catalytic cycle consists of a Volmer and a Heyrovsky step, with the latter being rate determining. In addition, we investigate for the first time the effect of a conductive support on the HER activity of these sulfur vacancies. Our results show that copper, gold and graphite supports have little effects on the activation energies of all steps. Hence, we conclude that cheap, acid-stable, high-surface area carbon supports are well suited for MoS2-based HER catalysts.

The interior NiCo2S4 nanotube skeletons supported MoS2 nanosheet arrays as advanced electrocatalysts for hydrogen evolution reaction

The hydrogen evolution reaction (HER) happens at the interface between the electrolyte and the electrocatalysts. Thus, the outer surface of electrocatalysts is regarded as the most important towards the catalytic performance, considering its direct contact with the electrolyte. However, the interior part of catalysts could also have an influence on the HER performances. Herein, the HER catalytic performances of MoS2 nanosheets are proven to be enhanced by the interior NiCo2S4 nanotube skeletons, although the interior skeletons are unaccessible for the electrolyte during the HER process. The reasons may lie in the optimized electronic transport properties and much increased amount as well as intrinsic activity of active sites. The theoretical calculations and experimental results suggest enhanced adsorption of H* and accelerated Heyrovsky step of the HER process for the NiCo2S4 supported MoS2, which may be the reason of the improved intrinsic activity of the active sites. Moreover, calculation of the densities of states suggests the metallic nature of the heterostructures, which could result in the excellent electronic transport performance for NiCo2S4 supported MoS2. In addition, the enhancement has a close relationship with the amount of the loading MoS2. Besides, compared with bared NiCo2S4 nanotubes, the MoS2 loaded NiCo2S4 nanostructures also exhibit better HER catalytic activity as well as improved catalytic stability. This work offers an effective and facile way to design and prepare efficient non-precious metal HER catalysts.

Improving the Efficiency of Gallium Telluride for Photocatalysis, Electrocatalysis, and Chemical Sensing through Defects Engineering and Interfacing with its Native Oxide

AbstractGallium telluride (GaTe) is a van der Waals semiconductor, currently adopted for photonic and optoelectronic devices. However, the rapid degradation of GaTe in air, promoted by Te vacancies, is detrimental for device applications. Here, it is demonstrate that the surface oxidation of GaTe can be unexpectedly exploited for expanding the breadth of applications of GaTe. Specifically, the formation of a nanoscale sub‐stoichiometric wide‐band‐gap Ga2O3 skin, promoted by Te vacancies, over narrow‐band‐gap GaTex upon air exposure is beneficial for electrocatalysis, photocatalysis, and gas sensing . In particular, the Heyrovsky step (Hads + H+ + e− → H2) of hydrogen evolution reaction in an acidic medium is barrier‐free for the sub‐stoichiometric gallium‐oxide/gallium‐telluride heterostructure, which also enables a significant reduction of costs with respect to state‐of‐the‐art Pt/C electrodes. In the photocatalytic process, the photo‐generated electrons migrate from GaTe to Ga2Ox skin, which acts as the chemically active side of the interface. Moreover, the Ga2O3/GaTe heterostructure is a suitable platform for sensing of H2O, NH3, and NO2 at operational temperatures extended up to 600 °C (useful for gas detection in combustion processes), mainly due to the increased area of charge redistribution after adsorption achieved upon oxidation of GaTe.

Circumventing the OCl versus OOH scaling relation in the chlorine evolution reaction: Beyond dimensionally stable anodes

The development of selective electrocatalysts for the chlorine evolution reaction (CER) is majorly restrained by a scaling relation between the OCl and OOH adsorbates, rendering that active CER catalysts are also reasonably active in the competing oxygen evolution reaction (OER). While theory predicts that the OCl versus OOH scaling relation can be circumvented as soon as the elementary reaction steps in the CER comprise the Cl rather than the OCl adsorbate, it was demonstrated recently that PtN 4 sites embedded in a carbon nanotube follow this theoretical prediction. Advanced experimental analyses illustrate that the PtN 4 sites also reveal a different reaction kinetics compared to the industrial benchmark of dimensionally stable anodes (DSA). A reverse Volmer–Heyrovsky mechanism was identified, in which the rate-determining Volmer step for small overpotentials is followed by the kinetically limiting Heyrovsky step for larger overpotentials. Since the PtN 4 sites excel DSA in terms of activity and chlorine selectivity, we suggest the Cl intermediate as well as the reverse Volmer–Heyrovsky mechanism as the design criteria for the development of next-generation electrode materials beyond DSA.

Direct photo-curing 3D printing of nickel-based electrocatalysts for highly-efficient hydrogen evolution

It is of great significance to develop cost-effective electrocatalysts for efficient and durable hydrogen evolution reaction (HER) in alkaline media to meet the increasing demand of hydrogen. Here, we report a photo-curing 3D printing method for manufacturing directly the structured nickel-based electrocatalysts with unique gluten-like cubic structure and strong catalyst-substrate interaction. With incorporation of amorphous titanium, the tailored Ti-Ni NS electrode exhibits excellent durability, a Tafel slop of 74 mV dec −1 of the HER, and a remarkable low overpotential of 34 mV at a current density of 10 mA cm−2, surpassing the commercial Pt/C catalyst and most of the state-of-the-art electrocatalysts. Density functional theory calculations further confirm that the Ti doping decreases significantly the energy barriers in the Volmer and Heyrovsky steps, thus favoring the HER. This work opens a new window of precisely preparing the structured noble-metal-free catalysts with enhanced activity in alkaline water electrolysis (AWE).

Fe Engineering on Ru Nanosheets for Enhanced Hydrogen Evolution in pH-Universal Media.

Fe-modified Ru nanosheets are achieved via preintercalated Al species serving as the self-sacrificial template. Benefiting from the amphoteric feature of Al and strong corrosion of Fe3+ ions, Fe is effectively incorporated into pristine Ru nanosheets. Correspondingly, the surface oxophilicity is improved, promoting the Volmer step. The charge density redistribution weakens hydrogen combination on Ru and thus accelerates the desorption kinetics (Heyrovsky step). Meanwhile, more defective sites are exposed, leading to an enhanced hydrogen production in pH-universal electrolytes.

Facile synthesis of novel molybdenum disulfide decorated banana peel porous carbon electrode for hydrogen evolution reaction

Hydrogen is one of the cleanest renewable and environmentally friendly energy resource that can be generated through water splitting. However, hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. In the present work, a novel molybdenum disulfide decorated banana peel porous carbon (MoS2@BPPC) catalyst has been developed using banana peel carbon and molybdenum disulfide (MoS2) for hydrogen evolution reaction (HER). Banana peel porous carbon (BPPC) was initially synthesized from the banana peel (biowaste) by a simple carbonization method. Subsequently, 20 wt% of bare MoS2 was distributed on the pristine BPPC matrix using the dry-impregnation method. The resulting MoS2@BPPC composites were systematically investigated to determine the morphology and structure. Finally, using a three-electrode cell system, pristine BPPC, bare MoS2, and MoS2@BPPC composite were used as HER electrocatalysts. The developed MoS2@BPPC composite showed greater HER activity and possessed excellent stability in the acid solution, including an overpotential of 150 mV at a current density of −10 mA cm−2, and a Tafel slope of 51 mV dec−1. This Tafel study suggests that the HER takes place by Volmer–Heyrovsky mechanism with a rate-determining Heyrovsky step. The excellent electrochemical performance of MoS2@BPPC composite for HER can be ascribed to its unique porous nanoarchitecture. Further, due to the synergetic effect between MoS2 and porous carbon. The HER activity using the MoS2@BPPC electrode advises that the prepared catalyst may hold great promise for practical applications.

Plasma-assisted highly dispersed Pt single atoms on Ru nanoclusters electrocatalyst for pH-universal hydrogen evolution

Exploring highly active and stable electrocatalyst using trace noble metals for hydrogen evolution reaction (HER) is urgently needed but still challenging. Here, atomically dispersed Pt on ultrafine Ru nanoclusters (∼1.46 nm) loaded by the commercial acetylene black (Acet) support is fabricated by a facile one-step cold-plasma technique. The Pt single atoms on Ru nanoclusters electrocatalyst (Pt0.47-Ru/Acet) with 0.47 wt% content of Pt exhibit an excellent HER activity in all pH, achieving ultralow overpotential of only 17, 28, and 8 mV at 10 mA·cm−2 in 1 M KOH, 0.5 M H2SO4, and 1 M PBS, respectively. And the mass activity of Pt0.47-Ru/Acet catalyst in alkaline is about 5.54 and 2.15 times that of commercial Ru/C and Pt/C catalyst at an overpotential of 100 mV, respectively. Meanwhile, after 8000 CV cycles, there is barely performance decrease for Pt0.47-Ru/Acet, displaying good stability. DFT calculation reveals that the Pt single atoms could effectively regulate the electronic structure of Ru clusters, and reduce the energy barriers of water dissociation (Volmer step) as well as subsequent hydrogen evolution (Heyrovsky step), thus enhancing the alkaline HER performance effectively. This work provides an effective approach to designing a high-performance HER electrocatalyst with the atomic-dimension Pt surface modification.

Heterostructured Palladium–Nickel Sulfide on Plasma-Activated Nickel Foil for Robust Hydrogen Evolution

Transition-metal sulfides are among the effective electrocatalyst candidates for H2 evolution (HER); however, they still cannot compete with Pt-based electrodes for renewable energy applications. To overcome this issue, grid-matched palladium–nickel sulfides (Pd4S/Ni3S2) are successfully engineered on the holey surface of nickel foil (HNF), which is first treated with a non-thermal plasma (HPNF) generated by a dielectric barrier discharge. The synthesized heterogeneous Pd4S-Ni3S2/HPNF catalyst results in the electron redistribution on the phase interfaces, enhancing the desorption ability of H* species. Consequently, Pd4S-Ni3S2/HPNF presents a high HER activity, and the overpotentials for generating 10 (j10) and 500 (j500) mA/cm2 are about 44 and 247 mV. Meanwhile, the catalyst retains good electrocatalytic stability over 50 h at j100. In addition, the H2 amount of Pd4S-Ni3S2/HPNF driven by the current j10 can reach 11.25 mmol/h, which is competitive with other presently available high-performance electrocatalysts. The theory and in situ Raman spectroscopy results indicate that Pd4S and the heterointerfaces between the Pd4S and Ni3S2 phases are the main active catalytic sites for H2 evolution and that the Pd weakens the S–Hads bonds, enhancing the reactive kinetics of the Volmer and Heyrovsky steps. This work provides a new and green approach for engineering highly active and stable electrocatalysts for clean hydrogen production.

Interfacial Engineering of a Phase-Controlled Heterojunction for High-Efficiency HER, OER, and ORR Trifunctional Electrocatalysis.

The development of low-cost and high-performance electrocatalysts for simultaneously boosting the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is highly crucial but still challenging. Herein, a facile one-step solid-phase polymerization and confined pyrolysis strategy is developed for scalable synthesis of a FexP/Fe3C-based (x = 1, 2) heterojunction with controllable iron phosphide crystal phases. By effective heterojunction interface regulation, the strong synergic effect between FeP/Fe3C and N- and P-codoped carbon (NPC) modified the electronic structure, resulting in an excellent electrocatalytic performance for the HER, OER, and ORR synchronously. Typically, the FeP/Fe3C@NPC catalyst exhibits efficient HER activity with a low overpotential of 10 mA cm–2 for the HER (97 mV) and OER (440 mV) and a high half-wave potential of 0.87 V for the ORR, as well as excellent stability in alkaline media. Theoretical calculations demonstrated that Fe3C can promote the activation of water molecules, while FeP is beneficial to the removal of H2 and the FeP/Fe3C heterojunction can facilitate both Volmer and Heyrovsky steps in the HER process simultaneously. Moreover, FeP has a stronger inhibitory effect on OH adsorption, revealing that the FeP/Fe3C heterojunction also shows a better promoting effect for both the OER and ORR, respectively.