Electrocatalytic Water Reduction Research Articles

Novel Gel method MXene-Supported Dual-Site PtNi-NiO for Electrocatalytic Water Reduction and Urea Oxidation.

Compared to the traditional oxygen evolution reaction (OER), the urea oxidation reaction (UOR) generally exhibits a lower overpotential during the electrolytic process, which is conducive to the hydrogen evolution reaction (HER) at the cathode. The superior structure and abundant sites play a crucial role in promoting the adsorption and cleavage of urea molecules. Therefore, this paper introduces a simple metal cation-induced gelation method to prepare an electrocatalyst with PtNi alloy-NiO dual sites supported on Ti3C2Tx, which simultaneously exhibits excellent UOR and HER performance. PtNi-NiOx/Ti3C2Tx demonstrates good catalytic activity for the urea oxidation reaction, requiring only 1.364V (overpotential of 0.994V) to achieve a current density of 100mAcm-2 in UOR, and also exhibits remarkable catalytic activity in the hydrogen evolution reaction, with PtNi-NiOx/Ti3C2Tx achieving a current density of 10mAcm-2 in HER with only 24mV of overpotential. In the UOR//HER two-electrode electrolysis cell, it requires only 1.361 and 1.538V to reach current densities of 10 and 100mAcm-2, respectively. According to density functional theory (DFT) calculations, the dual active sites can intelligently adsorb the electron-donating/electron-withdrawing groups in urea molecules, activate chemical bonds, and thereby initiate urea decomposition.

Rhombohedrally stacked layered transition metal dichalcogenides and their electrocatalytic applications.

Layered transition metal dichalcogenides (TMDCs) are extensively investigated as catalyst materials for a wide range of electrochemical applications due to their high surface area and versatile electronic and chemical properties. Bulk TMDCs are van der Waals solids that possess strong in-plane bonding and weak inter-layer interactions. In the few-layer 2D TMDCs, several polymorphic structures have been reported as each individual layer can either retain octahedral or trigonal prismatic coordination. Among them, 1T (tetragonal), 2H (hexagonal) and 3R (rhombohedral) phases are very common. These polymorphs can display discrepancies in their catalytic activity as their electronic structure diverges due to different d orbital filling states. The broken inversion symmetry and large exposed edge sites of some of the 3R-phase TMDCS such as MoS2, NbS2 and TaS2 appear to be advantageous for electrocatalytic water reduction and battery applications. We describe recent studies in phase engineering of 2D TMDCs, particularly aiming at the 3R polytype and their electrocatalytic properties. Redox ability primarily depends on a distinct polymorphic phase in which TMDCs are isolated, and hence, with rich polymorphic structures being reported, numerous new catalytic applications can be realized. Phase conversion from 2H to 3R phase in some TMDCs enhances structural integrity and establishes robustness under harsh chemical conditions.

Green fabrication of ultrafine N-Mo x C/CoP hybrids for boosting electrocatalytic water reduction

Developing non-noble-metal electrocatalysts for hydrogen evolution reactions with high activity and stability is the key issue in green hydrogen generation based on electrolytic water splitting. It has been recognized that the stacking of large CoP particles limits the intrinsic activity of as-synthesized CoP catalyst for hydrogen evolution reaction. In the present study, N-Mo x C/CoP-0.5 with excellent electrocatalytic activity for hydrogen evolution reaction was prepared using N-Mo x C as decoration. A reasonable overpotential of 106 mV (at 10 mA cm−2) and a Tafel slope of 59 mV dec−1 in 1.0 M KOH solution was achieved with N-Mo x C/CoP-0.5 electrocatalyst, which exhibits superior activity even after working for 37 h. Uniformly distributed ultrafine nanoclusters of the N-Mo x C/CoP-0.5 hybrids could provide sufficient interfaces for enhanced charge transfer. The effective capacity of the hydrogen evolution reaction could be preserved in the complex, and the enlarged electrocatalytic surface area could be expected to offer more active sites for the reaction.

High-temperature preparation of Ni2P suspended within carbon matrix and its potential as HER electrocatalyst

Hydrogen production via electrocatalytic reduction of water is a promising clean-energy technology. For further advancement of this technology, the exploration of cost-effective and streamlined approaches for producing active phosphide-based catalysts is of great importance. This study presents a new high-temperature preparation method of a microporous Ni2P/C catalyst composed of crystalline Ni2P nanoparticles homogeneously distributed within an amorphous carbon matrix in a weight ratio of 40/60. The redox transformation leading to the formation of Ni2P from not-reduced stable inorganic salts was facilitated during thermal treatment by a polymeric precursor, which, in turn, transformed into microporous carbon matrix that prevented the newly formed phosphide particles from agglomerating and sintering. The microporous structure of the prepared composite was characterised by gas adsorption technique and modelled using density functional theory and statistical thickness methods. The t-plot revealed high micropore surface area of 333.5 m2 g−1 (accounting 97 % of total surface area) and the pore size distribution in the range of 10–12 Å. According to TEM analysis, the size range of the Ni2P inclusions varied from 5 to 200 nm. The evaluation of electrocatalytic properties of the Ni2P/C composite demonstrated its high HER activity and stability under high voltages in alkaline water electrolysis conditions. Furthermore, HER activity of the composite was substantially enhanced by grinding, which opened closed microporosity channels and increased the micropore surface area to 355.2 m2 g−1, thereby increasing the number of catalytically active sites in the sample. The result indicates the exceptional role of the microporous microstructure of the composite in its catalytic performance. The findings of this study may have a significant impact on the practical implementation of efficient hydrogen production by water electrolysis.

Surface engineering of non-platinum-based electrocatalysts for sustainable hydrogen production: Encapsulation, doping, and decoration approach

The hydrogen evolution reaction's electrocatalytic reduction of water to molecular hydrogen may one day provide a long-term sustainable source of energy. However, the use of precious platinum catalysts makes it difficult to commercialize. So far, all alternatives to platinum are based on non-precious metals and transition metals. Hence, tuning the catalytic activity of nanomaterials through surface engineering might offer significant advantages. Herein, we step-wisely modulate the surface of all carbon fullerene nanomaterial by encapsulation, doping and decoration with alkali and transition metals to produce a hybrid catalyst which demonstrated excellent hydrogen evolution activity with comparable Gibbs free energy with both experimentally developed and theoretically modelled electrocatalyst. The adsorption of H* intermediate on the doped and decorated metal sites has been investigated in comparison with the pristine C24 fullerene structure. The electronic properties, the density of state (PDOS), reaction-free energy (ΔG) and transition states have all been carefully considered at appropriate theoretical levels. The ΔG of hydrogen adsorption on H@IndecNidopMgencC24 was found to be closer to zero (0.0328 eV) because of the concomitant effect of the encapsulation, doping and decoration with transition metals thus, demonstrating the effectiveness of this approach to tuning catalytic activity. The encapsulated metal enhanced the catalyst surface's conductivity and electronic attributes, leading to improved HER activity. The catalytic HER was also found to follow the Volmer-Tafel pathways, resulting in a lower free energy barrier. Overall, this work demonstrates a simple structure-activity relationship between metallic effects and substrate engineering and could open new dimensions for the development of novel non-platinum-based electrocatalysts.

Vacancy engineering in tungsten induced electronic structure optimization of MoSe2 for enhanced electrocatalytic hydrogen evolution reaction

Hydrogen (H2) is a clean and sustainable energy source, and it plays an integral part in lowering the world's reliance on fossil fuels. H2 evolution by the electrocatalytic reduction of water is a key step toward protecting the environment, and the development of cost-effective electrocatalysts is required for the production of huge quantities. In this article, metal (Tungsten)-doped molybdenum selenide (MoSe2) electrocatalysts for the hydrogen evolution process are proposed. MoSe2 activity in the hydrogen evolution process not only promotes the (selenium) Se vacancies and generation of phase shift from 2H to 1T but also optimizes the electronic structure of the material, which is favorable for hydrogen adsorption. Compared to pure P–MoSe2, engineered V–WMoSe2 nanosheets exhibit a low overpotential of ∼247 mV at a current density of 10 mA cm−2 and a lowered Tafel slope and decent turnover frequency (TOF). This technology not only explains the process behind the enhanced hydrogen evolution capabilities but also provides low-cost and effective Mo-based electrocatalysts by stimulating metal cations.

Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst

The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(–) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V.

Barrel-Shaped-Polyoxometalates Exhibiting Electrocatalytic Water Reduction at Neutral pH: A Synergy Effect.

Two copper-based barrel-shaped polyoxometalates (POMs), namely, [{H3O}4{Na6(H2O)22}][{CuI (H2O)3}2{CuII (H2O)}3{B-α-BiIIIWVI9O33}2]·7H2O (NaCu-POM) and Li4[{NH4}2{H3O}3{Li(H2O)5}][{CuII(SH)}{(CuIICuI1.5)(B-α-BiIIIWVI9O33)}2]·9H2O (LiCu-POM) have been synthesized and structurally characterized. The single-crystal X-ray diffraction analyses of NaCu-POM and LiCu-POM reveal the presence of penta- and hexa-nuclear copper wheels per formula units, respectively; these copper wheels are sandwiched between two lacunary Keggin anions {B-α-BiIIIWVI9O33}9- (BiW9) to form the barrel-shaped title POM compounds. In both the compounds NaCu-POM and LiCu-POM, the mixed-valent copper centers are present in their respective penta- and hexa-nuclear copper wheels, established by X-ray photoelectron spectroscopy (XPS) as well as by bond valence sum (BVS) calculations. Compound LiCu-POM additionally shows the presence of a sulfhydryl ligand (SH-), coordinated to one of the copper centers of its {Cu6}-wheel, that is expected to be generated from the in situ reduction of sulfate anion present in the concerned reaction mixture (lithium-ion in ammonia solution may be the reducing agent). Interestingly, the title compounds, NaCu-POM and LiCu-POM exhibit an efficient electrocatalytic hydrogen evolution reaction (HER) by reducing water at neutral pH. Detailed electrochemical studies including controlled experiments indicate that the active sites for this electrocatalysis are the W(VI) centers of the title compounds, not the copper centers. However, a relevant tri-lacunary Keggin cluster anion {PVWVI9O33}7- (devoid of copper ion) does not show comparable HER as shown by the title compounds. The intra-cluster cooperative interactions of the mixed-valent copper centers (CuII/CuI) with the tungsten centers (W6+) make the overall system electrocatalytically active toward water reduction to molecular hydrogen at neutral pH. High Faradaic efficiencies (89 and 92%) and turnover frequencies (1.598 s-1 and 1.117 s-1) make the title compounds NaCu-POM and LiCu-POM efficient catalysts toward electrochemical water reduction to molecular hydrogen.

Nanoblackberries of {W72Fe33} and {Mo72Fe30}: Electrocatalytic Water Reduction.

The reversible self-assembly of a {Mo72Fe30} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O ({Mo72Fe30}cryst) was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, {M72Fe30} (M = W, Mo) can be self-assembled into nanoblackberries irreversibly, leading to their solid-state isolation as the nanomaterials Fe3[W72Fe30O252(CH3COO)2(OH)25(H2O)103]·180H2O ({W72Fe33}NM) and Na2[Mo72Fe30O252(CH3COO)4(OH)16(H2O)108]·180H2O ({Mo72Fe30}NM), respectively (NM stands for nanomaterial). The formulations of these one-pot-synthesized nanoblackberries of {W72Fe33}NM and {Mo72Fe30}NM have been established by spectral analysis including Raman spectroscopy, elemental analysis including ICP metal analysis, volumetric analysis (for iron), microscopy techniques, and DLS studies. The thermal stability of the tungsten nanoblackberries {W72Fe33}NM is much higher than that of its molybdenum analogue {Mo72Fe30}NM. This might due to the extra three ferric (Fe3+) ions per {W72Fe30} cluster in {W72Fe33}NM, which are not part of the {W72Fe30} cluster cage but are placed between two adjacent clusters (i.e., each cluster has six surrounding 0.5Fe3+) to form this self-assembly. The isolated blackberries behave like an inorganic acid, a water suspension of which shows pH values of 3.9 for {W72Fe33}NM and 3.7 for {Mo72Fe30}NM because of the deprotonation of the hydroxyl groups in them. We have demonstrated, for the first time, a meaningful application of these inexpensive and easily synthesized nanoblackberries by showing that they can act as electrocatalysts for the hydrogen evolution reaction (HER) by reducing water. We have performed detailed kinetic studies for the electrocatalytic water reduction catalyzed by {W72Fe33}NM and {Mo72Fe30}NM in a comparative study. The relevant turnover frequencies (TOFs) of {W72Fe33}NM and {Mo72Fe30}NM (∼0.72 and ∼0.45 s-1, respectively), the overpotential values of {W72Fe33}NM and {Mo72Fe30}NM (527 and 767 mV, respectively at 1 mA cm-2), and the relative stability issues of the catalysts indicate that {W72Fe33}NM is reasonably superior to {Mo72Fe30}NM. We have described a rationale of why {W72Fe33}NM performs better than {Mo72Fe30}NM in terms of catalytic activity and stability.

Polyoxometalate based hybrid compound as a pre-catalyst for electrocatalytic water reduction at neutral pH

Polyoxometalate based hybrid compound as a pre-catalyst for electrocatalytic water reduction at neutral pH

Unusual Formation of CoS0.61Se0.25 Anion Solid Solution with Sulfur Defects to Promote Electrocatalytic Water Reduction

Defects engineering is an effective strategy to promote electrocatalytic performance. Herein, cobalt binary chalcogenide hollow spheres (CBC HSs) with sulfur (S) defects were prepared by selenium (...

Tuning Cu Overvoltage for a Copper-Telluride System in Electrocatalytic Water Reduction and Feasible Feedstock Conversion: A New Approach.

Highly efficient and earth-abundant elements capable of water reduction by electrocatalysis and are attractive for the sustainable generation of fuels. Among the earth-abundant metals, copper is one of the cheapest but often the most neglected choice for the hydrogen evolution reaction (HER) due to its high overvoltage. Herein, for the first time we have tuned the overpotential of copper by tellurizing it by two different methodologies, viz. hydrothermal and wet chemical methods, which form copper telluride nanochains and aggregates. The application of copper telluride as an electrocatalyst for the HER gave fruitful results in terms of both activity and stability. The hydrothermally synthesized catalyst Cu2-xTe/hyd shows a low overpotential (347 mV) at 10 mA cm-2 toward the HER. In addition, the catalyst showed a very low charge transfer resistance (Rct) of 24.4 Ω and, as expected, Cu2-xTe/hyd exhibited a lower Tafel slope value of 188 mV/dec in comparison to Cu2-xTe/wet (280 mV/dec). A chronoamperometry study reveals the long-term stability of both catalysts even up to 12 h. The Faradaic efficiency of Cu2-xTe/hyd was calculated and found to be 95.06% by using gas chromatographic (GC) studies. Moreover, with the idea of utilizing produced hydrogen (H2) from electrocatalysis, for the first time we have carried out feedstock conversion to platform chemicals in water under eco-friendly green conditions. We have chosen cinnamaldehyde, 2-hydroxy-1-phenylethanone, 4-(benzyloxy)benzaldehyde, and 2-(3-methoxyphenoxy)-1-phenylethanone (β-O-4) as model compounds for feedstock conversion by hydrogenation and/or hydrogenolysis reactions in aqueous medium using external hydrogen pressure. This protocol could also be scaled up for large-scale conversion and the catalyst is likely to find industrial application since it requires an inexpensive catalyst and an easily available, mild reducing agent. The robustness of the developed catalyst is proven by recyclability experiments and its possibility of use in real-life applications.

Hydrophilic/Aerophobic Hydrogen-Evolving Electrode: NiRu-Based Metal-Organic Framework Nanosheets In Situ Grown on Conductive Substrates.

Electrocatalytic reduction of water via hydrogen evolution reaction (HER) is considered one of the most ideal avenues to produce high-purity hydrogen (H2) in large quantities, which always requires active electrocatalysts to overcome the high energy barrier. It is of significance yet challenging to design and construct effective HER electrocatalysts of an acceptable cost. In this study, a highly efficient metal-organic framework (MOF)-based electrochemical HER system based on NiRu-based binary MOF (Ru-doped Ni2(BDC)2TED MOF, BDC = 1,4-benzenedicarboxylic acid; TED = triethylenediamine) nanosheets grown on conductive substrates (e.g., Ni foam, carbon cloth) is fabricated by a facile solvothermal method. The resultant NiRu-MOF-based composites possess enhanced electron transport ability and water stability, accompanied by increased electrochemically active areas and hydrophilic/aerophobic properties. With these advantages, the optimized NiRu-MOF nanosheet arrays on Ni foam substrate (NiRu-MOF/NF) with a Ru/Ni molar ratio of 6/94 in the MOF structure could exhibit efficient catalytic performance for HER in alkaline conditions, requiring a small overpotential of 51 mV at -10 mA cm-2. This study could provide a feasible way for the design and synthesis of two-dimensional (2D) MOF-based materials with controllable interface properties for energy catalysis and beyond.

Visible-light-enhanced electrocatalytic hydrogen production on semimetal bismuth nanorods

Controlling the compositions and morphologies of the electrocatalysts were conventionally used for improving the catalytic activities. Here, visible-light-enhanced electrocatalytic water reduction reactions on semimetal bismuth (Bi) nanorods were achieved. The Bi catalyst not only exhibited an ideal Faradaic efficiency of 98% for electrocatalytic hydrogen production, but also acted as a light absorber for improving the activity even under light irradiation up to 740 nm. As a result, the solar-to‑hydrogen conversion efficiency under simulated AM 1.5G illumination was reached to 0.82%, which is 2.7 times higher than that induced by plasmon Au nanoparticles. This conversion efficiency is attributed to the excellent solar light absorption property of Bi and the enhanced electron-transfer at the interface of Bi/electrolyte under irradiation. The low-cost Bi catalyst with the dual function could open a venue toward designing more-energy-efficient electrocatalysts for hydrogen production assisted by sunlight.

Hydrogenase Enzyme like Nanocatalysts FeS2 and FeSe2 for Molecular Hydrogen Evolution Reaction

Hydrogen generation through electrocatalytic water reduction using copious and scalable electrocatalyst is one of the potential method to produce clean energy. Transition metal dichalcogenides with appropriate band potential have been demonstrated as potential electrocatalysts for hydrogen evolution reaction (HER). Here in we have synthesized nanostructured FeS2 and FeSe2 that possess defined and irregular shaped flower like morphology using solvothermal reduction method. X-ray powder diffraction (XRD) confirms the pyrite FeS2 (iron disulfide) and orthorhombic phase FeSe2 (iron diselenide) and compared it’s HER catalytic performance. FeSe2 exhibited lower over potential of 113 mV with a current of 2 mA/cm2 (10 mA/cm2 current at 244 mV) compared to FeS2 with over potential 453 mV. The improved catalytic behavior of FeSe2 can be attributed to favourable bond strength between selenide and hydrogen (276 kJ/mol) which is about 87 kJ/mol lesser than FeS2 (363 kJ/mol).

The mechanistic role of a support-catalyst interface in electrocatalytic water reduction by Co3O4 supported nanocarbon florets.

Comprehending the mechanistic involvement of a support-catalyst interface is critical for effective design of industrially relevant electrocatalytic processes such as the alkaline hydrogen evolution reaction (alHER). The understanding of the kinetically sluggish alHER exhibited by both Pt and Pt-group-metal-free catalysts is primarily derived from indirect electrochemical parameters such as the Tafel slope. To address these issues, we establish the critical role of a nanocarbon floret (NCF) based electrochemical support in generating a key cobalt-oxohydroxo (OH-Co[double bond, length as m-dash]O) intermediate during the alHER through operando Raman spectro-electrochemistry. Specifically, interfacial nano-engineering of a newly designed carbon support (NCF) with a spinel Co3O4 nanocube catalyst is demonstrated to achieve a facile alHER (-0.46 V@10 mA cm-2). Such an efficient alHER is mainly attributed to the unique lamellar morphology with a high mesoporous surface area (936 m2 g-1) of the NCF which catalyses the rate-determining water dissociation step and facilitates rapid ion diffusion. The dissociated water drives the formation of the OH-Co[double bond, length as m-dash]O intermediate, spectroscopically captured for the first time through the emergence of a νOH-Co[double bond, length as m-dash]O Raman peak (1074 cm-1). The subsequent alHER proceeds through the Volmer-Heyrovsky route (119 mV dec-1) via the Td Co2+↔ Co3+↔ Co4+ oxidative pathway. Concomitant graphitization of the NCF through the disappearance of νsp3C-H (2946 cm-1) supports the co-operative dynamics at the Co3O4-NCF interface. Thus, the NCF positively contributes towards the lowering of the overpotential with a low charge-transfer resistance (Rct = 35.8 Ω) and high double layer capacitance (Cdl = 410 mF cm-2).

Virus-templated Pt–Ni(OH)2 nanonetworks for enhanced electrocatalytic reduction of water

Clean hydrogen production via water electrolysis is incumbent upon the development of high-performing hydrogen evolution reaction electrocatalysts. Despite decades of commercial maturity, however, alkaline water electrolyzers continue to suffer from limitations in electrocatalytic activity and stability, even with noble metal catalysts. In recent years, combining platinum with oxophilic materials, such as metal hydroxides, has shown great promise for improving performance potentially by enabling stronger water dissociation at the surface of electrocatalysts. In this work, we leveraged the nanoscopic proportions and surface programmability of the filamentous M13 bacteriophage in the design, synthesis, and exceptional performance of 3D nanostructured biotemplated electrocatalysts for alkaline hydrogen evolution. We developed a facile synthesis method for phage-templated, Pt–Ni(OH)2 nanonetworks, relying on scalable techniques like electroless deposition. After optimization of the platinum content, our materials display –4.9 A mg–1Pt at −70 mV versus the reversible hydrogen electrode, the highest reported mass activity in 1 M KOH to date, and undergo minimal changes in overpotential under galvanostatic operation at −10 mA cm–2geo. Looking forward, the performance of these catalysts suggests that biotemplating nanostructures with M13 bacteriophage offers an interesting new route for developing high-performing electrocatalysts.

Influence of Applied Potential, Water Content and Forced Convection on the Electrodeposition of Ni Films on Steel from Choline Chloride Based Deep Eutectic Solvents

Electrochemically deposited Ni coatings are widely used in the aviation, automotive, telecommunication and electronic industry because of their unique mechanical, protective and decorative properties. These films are commonly deposited from aqueous electrolytes due to the simplicity and cost-effectiveness of the processes. However, the use of water-based baths is related to several issues, i.e. water reduction and hydrogen gas formation that lead to the formation of pores and cracks which result into more brittle coatings. A promising alternative to avoid these problems is to use non-aqueous electrolytes such as Deep Eutectic Solvents (DESs). The feasibility of electroplating Ni and its alloys from choline chloride based DESs has been reported by several research groups [1–3]. In this context, recent studies have been focusing on the use of water as an additive. In most of the cases, just a small addition of water to those non-aqueous electrolytes is beneficial due to a decrease of viscosity and an increase of conductivity [3,4]. However, the electrocatalytic reduction of water during electrodeposition from DESs has also been shown to result into complex chemical and electrochemical processes that have a strong influence in the structure and morphology of the electrodeposited metallic phase [5]. Moreover, industrial electroplating processes are always carried out under forced convection to increase process efficiency and reduce deposition time. The interplay between electrodeposition kinetics and the mass transport of reactants and byproducts of the Ni electrodeposition from DESs has not been evaluated in detail yet. Similarly, the influence of applied potential on the structure and morphology of Ni coatings electrodeposited from DESs, as well as the effect on the electrochemical reduction processes are so far not fully understood. In this presentation, we report on the inter-related effects of water content, applied potential and forced convection in Ni electrodeposition on steel from 1 choline chloride (ChCl): 2 urea (U) DESs. Electrochemical methods such as cyclic voltammetry (CV) and chronoamperommetry (CA) were combined with surface analysis techniques (field emission scanning microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy) in order to understand the occurring phenomena under both stagnant and forced convection conditions. The influence of mass transport on Ni electrodeposition process was studied by linear sweep voltammetry in combination with a rotating disk electrode (LSV-RDE). The obtained results allowed a better understanding of the complex chemical and electrochemical processes occurring at the electrode surface depending on the mass transport conditions, applied potential and water content, which may result into the formation of NiO-OH and incorporation of DES decomposition by-products in the growing films. [1] A.P. Abbott, A. Ballantyne, R.C. Harris, J.A. Juma, K.S. Ryder, G. Forrest, "A Comparative Study of Nickel Electrodeposition Using Deep Eutectic Solvents and Aqueous Solutions", Electrochim. Acta. 176 (2015) 718–726. [2] L. Anicai, A. Florea, T. Visan, "Studies Regarding the Nickel Electrodeposition from Choline Chloride Based Ionic Liquids", Appl. Ion. Liq. Sci. Technol. (2011) 261–286. [3] V.S. Protsenko, A.A. Kityk, D.A. Shaiderov, F.I. Danilov, "Effect of water content on physicochemical properties and electrochemical behavior of ionic liquids containing choline chloride, ethylene glycol and hydrated nickel chloride", J. Mol. Liq. 212 (2015) 716–722. [4] C. Du, B. Zhao, X.-B. Chen, N. Birbilis, H. Yang, "Effect of water presence on choline chloride-2urea ionic liquid and coating platings from the hydrated ionic liquid", Sci. Rep. 6 (2016) 29225. [5] E.A. Mernissi Cherigui, K. Sentosun, P. Bouckenooge, H. Vanrompay, S. Bals, H. Terryn, J. Ustarroz, "Comprehensive Study of the Electrodeposition of Nickel Nanostructures from Deep Eutectic Solvents: Self-Limiting Growth by Electrolysis of Residual Water", J. Phys. Chem. C. 121 (2017) 9337–9347.

Design of Boron Doped C2N-C3N Coplanar Conjugated Heterostructure for Efficient HER Electrocatalysis

Hydrogen evolution reaction (HER) via the electrocatalytic reduction of water on metal-free catalysts may become a promising method for a sustainable energy supply in the future. However, compared with noble metals or transition metals, the carbon-based metal-free electrocatalysts show poor activity. Here, a novel coplanar metal-free catalyst (C2N-C3N) was designed for the first time to achieve better efficiency for electron transfer and water reduction. Through the DFT calculations, we discovered that the unique coplanar C2N-C3N structure can promote the directional transfer of electrons from C3N to C2N under the drive of built-in electric potential in the π-conjugated plane. To achieve higher performance in HER, the single atom doping by the substitution of boron is carried out. Remarkably, after the boron is doped, the barrier in the Tafel step decreases from 2.35 eV to 0.86 eV. Our results indicate that the novel B-doped coplanar C2N-C3N structure is a promising metal-free catalyst for HER.

A cobalt complex of a pentadentate aminopyridine ligand as an efficient catalyst for photocatalytic hydrogen generation

A linear pentadentate aminopyridine ligand 2,6-bis[(methyl(pyrid-2-ylmethyl)amino)-N-methyl]pyridine (PyMepam) has been prepared and characterized. This ligand readily coordinates with Co(II) or Zn(II) ions, and the resulting complexes of general formula [M(PyMepam)](BF4)2 (M=Co (1) and M=Zn (2)) have been thoroughly characterized and investigated for electro- and photocatalytic water reduction in acetonitrile. Electrochemical studies reveal that the complex 1 is active for electrocatalytic water reduction in acetonitrile. Under visible-light irradiation (λ>400nm), the complex 1 displays hydrogen evolution activity when in presence of [Ir(ppy)2(bpy)]PF6 as photosensitizer and triethylamine (TEA) as electron donor, whereas 2 shows negligible catalytic activity under the same conditions. Highest turnover numbers (TONs) of 290 for H2 evolution are achieved from an optimized system containing 1 (0.1mM), [Ir(ppy)2(bpy)](PF6) (0.5mM), and 10vol% TEA in CH3CN-H2O (1/1, v/v) mixed solvents at pH10.