Mechanism Of Hydrogen Evolution Research Articles

Reaction coordinate mapping of hydrogen evolution mechanism on Mg3N2 monolayer

In this work, we have envisaged the hydrogen evolution reaction (HER) mechanism on Mg3N2 monolayer based on electronic structure calculations within the framework of density functional theory (DFT) formalism. The semiconducting nature of Mg3N2 monolayer motivates us to investigate the HER mechanism on this sheet. We have constructed the reaction coordinate associated with HER mechanism after determining the hydrogen adsorption energy on Mg3N2 monolayer, while investigating all possible adsorption sites. After obtaining the adsorption energy, we subsequently obtain the adsorption free energy while adding zero point energy difference (ΔZPE) and entropic contribution (TΔS). We have not only confined our investigations to a single hydrogen, but have thoroughly observed the adsorption phenomena for increasing number of hydrogen atoms on the surface. We have determined the projected density of states (DOS) in order to find the elemental contribution in the valence band and conduction band regime for all the considered cases. We have also compared the work function value among all the cases, which quantifies the amount of energy required for taking an electron out of the surface. The charge transfer mechanism is also being investigated in order to correlate with the HER mechanism with amount of charge transfer. This is the first attempt on this material to the best of our knowledge, where theoretical investigation has been done to mapping the reaction coordinate of HER mechanism with the associated charge transfer process and the work function values, not only for single hydrogen adsorption, but also for increasing number of adsorbed hydrogen.

INVESTIGATION OF THE INHIBITION OF COPPER AND Α-BRASS CORROSION IN NITRIC ACID SOLUTIONS BY PISTACIA ATLANTICA EXTRACT

The detailed study of Pistacia Atlantica Extract (PAE) as corrosion inhibitor for copper and α-brass in nitric acid solution has been performed through potentio dynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) measurements. The effect of inhibitor concentration and immersion time against inhibitor action was investigated. Results show that PAE may be used as an efficient inhibitor for copper and α-brass in nitric acid solutions. Potentiodynamic polarization studies reveal that PAE acts as a mixed type inhibitor without any change in the mechanism of hydrogen evolution.

Synergy between van der waals heterojunction and vacancy in ZnIn2S4/g-C3N4 2D/2D photocatalysts for enhanced photocatalytic hydrogen evolution

Fabricating 2D/2D heterojunction with vacancy is more favorable to the spatial separation and transfer of charge owing to the matching of unique 2D structure and vacancy engineering, but the regulation and observation of interlayer forces and electronic structure is a challenging task for synthesizing heterojunction photocatalyst and studying the photocatalytic hydrogen evolution mechanism. Herein, an original 2D/2D ZnIn2S4/g-C3N4 Van der Waals heterojunction with S vacancies (ZIS-S/CN VDW) photocatalyst are firstly engineered. The optimized 30ZIS-S/g-C3N4 has the highest H2 evolution rate of 6095.1 μmol h−1 g−1, which is primarily attributed to the fact that 2D/2D VDW heterojunction possesses larger contact area and strong electronic interaction to stimulate charge kinetics, and the vacancy engineering can enhance light absorption by regulating the electronic band structure and act as effective active sites for capturing electrons. This work not only enriches 2D/2D heterojunction photocatalytic system based on g-C3N4, but also provides alternative proposal for engineering 2D/2D heterojunction photocatalyst with satisfactory performance.

Surface oxygen vacancy facilitated Z-scheme MoS2/Bi2O3 heterojunction for enhanced visible-light driven photocatalysis-pollutant degradation and hydrogen production

An oxygen-vacancy rich, bismuth oxide (Bi2O3) based MoS2/Bi2O3 Z-scheme heterojunction catalyst (2-BO-MS) was prepared in an autoclave hydrothermal method using ethanol and water. The performance of MoS2/Bi2O3 catalyst was examined for photocatalytic hydrogen evolution, photoelectrochemical activity, and crystal violet (CV) dye degradation by comparing with pristine Bi2O3 and MoS2. The hydrogen evolution performances of 2-BO-MS catalyst exhibited 3075.21 μmol g−1 h−1, which is 7.18 times higher than that of MoS2 (428.14 μmol g−1 h−1). The XPS, XRD and HRTEM analyses covered that the superior photocatalytic performance of 2-BO-MS catalyst might have stemmed out due to the existence of oxygen vacancies, enhanced strong interfacial interaction between MoS2 and Bi2O3 and specific surface area. The in-depth investigation has been performed for MoS2/Bi2O3 Z-scheme heterojunction using several characterization techniques. Moreover, the photocatalytic mechanism for hydrogen evolution and photodegradation were proposed based on trapping experiment results. This results acquired using MoS2/Bi2O3 Z-scheme heterojunction would be stepping stone for developing heterojunction catalyst towards attaining outstanding photocatalytic activity.

Preparation of PtAuFe/C composite catalyst and performance for hydrogen evolution reaction

In this paper, PtAuFe/C composite catalyst and Pt/C catalyst are prepared by sodium borohydride direct reduction method. The physical properties of the catalysts are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The electrocatalytic hydrogen evolution performance of the prepared catalysts is tested by linear scanning voltammetry (LSV) in H2SO4 solution. The results show that the PtAuFe/C composite catalyst has larger specific surface area, smaller overpotential, higher polarization current density and better stability than that of the Pt/C catalyst. The hydrogen evolution mechanism of PtAuFe/C composite catalyst is determined by Tafel curve, and the results show that PtAuFe/C composite catalyst is of composite desorption mechanism. In addition, the effect of temperature and electrolyte concentration on the performance of PtAuFe/C composite catalyst is also studied.

Buffer pKa Impacts the Mechanism of Hydrogen Evolution Catalyzed by a Cobalt Porphyrin-Peptide.

The effect of buffer pKa on the mechanism of electrochemical hydrogen evolution catalyzed by a cobalt porphyrin peptide (CoMP11-Ac) at constant pH is presented. The addition of buffer to CoMP11-Ac in water and KCl leads to an enhancement of the catalytic current of up to 200-fold relative to its value in the absence of a buffer. Two distinct catalytic regimes are identified as a function of the buffer pKa. In the presence of buffers with pKa ≤ 7.4, a fast catalysis regime limited by diffusion of buffer is reached. The catalytic half-wave potential (Eh) shifts anodically (from -1.42 to -1.26 V vs Ag/AgCl/KCl(1M)) as the buffer pKa decreases from 7.4 to 5.6, proposed to result from fast Co(III)-H formation following the catalysis-initiating Co(II/I) reduction. With higher-pKa buffers (pKa > 7.7), an Eh = -1.42 V, proposed to reflect the Co(II/I) couple, is maintained independent of the buffer pKa, consistent with rate-limiting Co(III)-H formation under these conditions. We conclude that the buffer species pKa impacts catalytic current and potential and the rate-determining step of the reaction.

Facile synthesis of sulfur-doped Ni(OH)2 as an efficient co-catalyst for g-C3N4 in photocatalytic hydrogen evolution

Abstract In this study, sulfur-doped Ni(OH)2 was prepared by an immersion method at room temperature and used as an efficient co-catalyst for g-C3N4 in photocatalytic hydrogen evolution. The structure, morphology, and elemental composition of the sulfur-doped Ni(OH)2/g-C3N4 were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. These results proved that the sulfur-doped Ni(OH)2 was successfully synthesized and combined with g-C3N4 at the heterojunction. The photocatalytic hydrogen generation results of Ni(OH)2/g-C3N4 (0 μmol g−1 h−1) and that of sulfur-doped Ni(OH)2/g-C3N4 (1573.7 μmol g−1 h−1) indicate that the sulfur doping resulted in significant improvement in the catalytic activity of co-catalyst Ni(OH)2. Moreover, the possible mechanism of photocatalytic hydrogen evolution catalyzed by the sulfur-doped Ni(OH)2/g-C3N4 was proposed. The results of photoluminescence, ultraviolet–visible diffuse reflectance spectroscopy, and electrochemical analysis demonstrated that the sulfur doping provided more active sites in Ni(OH)2, leading to the efficient hydrogen evolution reaction, thus indirectly enhancing the separation efficiency of electron–hole pairs and the migration efficiency of photogenerated electrons by the photocatalyst g-C3N4.

New Insights of the pH Effect on Hydrogen Evolution and Oxidation Reactions Mechanisms in Alkaline Solutions

The sluggish kinetics of the hydrogen evolution and oxidation reactions (HER/HOR) of Pt in alkaline solutions than in acid remains elusive. Elucidation of the mechanisms of the HER/HOR in alkaline can not only deepen our understandings of alkaline electrochemistry, but also help to rationalize the design of highly active catalysts for alkaline fuel cells and electrolyzers. Herein, we investigate the HER/HOR kinetics of a variety of catalysts including monometallic catalysts (Ni, Pt, Ru, Au) and bimetallic catalysts (NiMo, Pt-M) by comparing their HER/HOR performance in 0.1 M KOH and 1 M KOH. We found that the HER/HOR kinetics of these systems are not always slower in 1 M KOH (pH =14) than in 0.1 M KOH (pH = 13). These observations do not follow the general trend that the HER/HOR kinetics of a wide range of elements slows down with increasing pH1. We propose to resolve this inconsistency by pointing out that the pH is only one of the factors that affect the transport of the HER/HOR intermediates (hydroxyl for HER, Had for HOR) throughout the double layer region, among other factors such as the oxophicility of the surface sites, the cation environment, etc. These factors co-determine the HER/HOR kinetics of catalysts (such as Pt/C) that is limited by the transport of reactions throughout the double layer region. As the electrolyte changes from 0.1 M KOH to 1 M KOH, the pH shifts from 13 to 14, slowing down the HER/HOR kinetics. Meanwhile, the K+ concentration increases one order of magnitude, which promotes the transport of OHad according to the hard-soft acid-base (HSAB) mechanism we proposed recently2, thereby improving the HER but not the HOR until the K+ saturates. The change of the HER/HOR kinetics of a catalyst as the electrolyte changes from 0.1 M KOH to 1 M KOH is a counterbalance between these two effects, and thus varies case by case. Acknowledgements.This work was supported by the Department of Energy (DOE) under award number DE-EE0008082, Office of Naval Research (ONR) under award number N00014-18-1-2155 and the Graduate Thesis/Dissertation Grant of Northeastern University. This research used beamline 7-BM (QAS) and 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. References (1) Herranz, J.; Durst, J.; Fabbri, E.; Patru, A.; Cheng, X.; Permyakova, A. A.; Schmidt, T. J. Interfacial Effects on the Catalysis of the Hydrogen Evolution, Oxygen Evolution and CO2-Reduction Reactions for (Co-)Electrolyzer Development. Nano Energy 2016, 29, 4–28.(2) Liu, E.; Li, J.; Jiao, L.; Doan, H. T. T.; Liu, Z.; Zhao, Z.; Huang, Y.; Abraham, K. M.; Mukerjee, S.; Jia, Q. Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation Adducts. J. Am. Chem. Soc. 2019, 141 (7), 3232–3239.

Buffer Pka Impacts the Mechanism of Hydrogen Evolution in Water Catalyzed By a Cobalt Porphyrin-Peptide

A detailed study of the impact of buffer pKa (pKa 5.6 to 10.5) on electrochemical hydrogen evolution at constant pH catalyzed by CoMP11-Ac, a cobalt porphyrin peptide, is presented. The addition of buffer leads to a significant enhancement of the catalytic current of up to 20-fold relative to its value in absence of buffer. Two distinct catalytic regimes are identified based on the buffer pKa . In the presence of buffers with pKa ≤ 7.4 a fast catalysis regime limited by diffussion of buffer is reached. The catalytic half-wave potential (Eh ) shifts anodically (from -1.42 to -1.26 V vs Ag/AgCl/KCl(1M)) as the buffer pKa decreases from 7.4 to 5.6, proposed to result from fast Co(III)-H formation following the catalysis-initiating Co(II/I) reduction. With higher-pKa buffers (pKa > 7.7), an Eh = -1.42 V reflecting the potential of the Co(II/I) couple is maintained independent of the buffer pKa , consistent with a rate-limiting Co(III)-H formation under these conditions. We conclude that the buffer species pK a, even at constant pH, can have a large effect on both catalytic current and potential, as well as the rate-determining step of the reaction. Thus, buffer is a factor to consider in optimizing reaction conditions for hydrogen-evolving catalysis and for other proton-requiring reactions in water. Finally, buffer acids are shown to be a probe for studying hydrogen evolution mechanism in water.

Efficient photocatalytic hydrogen evolution over MoS2/activated carbon composite sensitized by Erythrosin B under LED light irradiation

MoS2 is a promising catalyst for hydrogen evolution reaction, whereas the inherent defects of limited active sites for H2 evolution and poor conductivity impede its practical application. Herein, low-cost and available activated carbon (denoted as C) was introduced and MoS2/C composite was prepared via a facile one-pot liquid-phased reaction. The MoS2/C exhibits an excellent photocatalytic hydrogen evolution activity (872.3 μmol/h) sensitized by Erythrosin B under LED light irradiation, which is about 1.8 times that of pure MoS2. Moreover, hydrogen evolution mechanism and reasons for the enhanced performance of MoS2/C were proposed based on the results of photoluminescence spectra and photoelectrochemical tests.

Sulfur Doped Carbon-Rich g-C3N4 for Enhanced Photocatalytic H2 Evolution: Morphology and Crystallinity Effect

Molecular design for the intercalation of S and C in the framework of g-C3N4 is a promising strategy to increase visible light harvesting and facilitate the separation of photoinduced electron/hole pairs. Herein, we reported a facial method to prepare porous S doped g-C3N4 nanotubes by thermal polymerization of urea and 2-thiobarbituric acid. The obtained catalysts contain certain carbon and sulfur atoms in the aromatic rings substituting the nitrogen atoms in g-C3N4, which narrows down the band gap, and increases the separation of photoinduced charge carriers. Meanwhile, nanotube formation increases the specific surface area of catalyst. The synergistic effect of S doped carbon rich g-C3N4 and nanostructure forming results in superior photocatalytic H2 evolution from water splitting. The study shows that the photocatalytic H2 evolution is correlated with the crystallinity of S doped g-C3N4. Schematic illustration for framework of 0.3S-CN and its photocatalytic hydrogen evolution mechanism.

Neutral heteroleptic nickel complexes incorporating maleonitriledithiolate and bis(diphenylphosphanyl)amine as robust molecular electrocatalysts for hydrogen evolution

Five neutral heteroleptic maleonitriledithiolate nickel complexes [RN(PPh2)2Ni(mnt)] bearing bis(diphenylphosphanyl)amine ligands (where mnt2− = maleonitriledithiolate; R = CH3O(CH2)3 (1), CH3S(CH2)3 (2), (S)-CH3CHPh (3), (CH3)2CH(CH2)2 (4), and p-CH3C6H4 (5)) have been synthesized and fully characterized by elemental analysis, FTIR, NMR (1H, 13C, and 31P) spectroscopy, UV–Vis spectrum, single crystal X-ray diffraction, thermogravimetric analysis, and density functional theory (DFT) calculation. The nickel atom in 1, 2, 4, and 5⋅1.5CH2Cl2 adopts a slightly distorted square-planar coordination environment with two phosphorus atoms of RN(PPh2)2 and two sulfur atoms of mnt2−, respectively, while the nickel atom in 3 exhibits a pseudo square pyramid with HP2S2 chromophore. Furthermore, the electrochemical properties for 1–5 were also investigated by cyclic voltammetry. With the addition of 120 mM trifluoroacetic acid (TFA) to 1–5 in MeCN, the turnover frequency (TOF) values are estimated to be 368.59–585.17 s−1 with the corresponding overpotential (η) values of 0.59–0.73 V. The electrochemical studies indicate that all complexes can be used as low-cost robust molecular eletrocatalysts for the reduction protons to hydrogen in the presence of TFA and a possible ECEC mechanism for electrocatalytic hydrogen evolution has been also proposed.

Consciously Constructing the Robust NiS/g-C3N4 Hybrids for Enhanced Photocatalytic Hydrogen Evolution

Selective growth of cocatalyst on the surface of photocatalyst has been attracted considerable attention due to their efficient charges transfer property. In this study, the robust NiS modified graphitic carbon nitride (g-C3N4) hybrids were successfully synthesized by a facile surface photochemical deposition process. The structure and composition characterization results revealed that the NiS is highly dispersed loading on the surface of g-C3N4 nanosheets, and the NiS/g-C3N4 hybrids possess large surface areas and excellent optical properties. Under the visible light illumination, the NiS/g-C3N4 hybrids with 1.0% weight content of NiS cocatalyst exhibits the highest hydrogen evolution rate of 1346.1 μmol h−1 g−1 with an apparent quantum efficiency (AQE) of 7.67%. On the basis of photoluminescence (PL) spectra and photoelectrochemical methodology, the photocatalytic hydrogen evolution mechanism was proposed. The results demonstrated that the excellent activity arises from the strong electronic coupling, highly efficient charges separation and migration. This work demonstrates a facile photochemical deposition method to consciously construct the robust two-dimensional (2D) hybrids, so as to realize accurate deposition of cocatalyst and efficient migration of photo-generated carriers.

Mechanism for hydrogen evolution from water splitting based on a MoS2/WSe2 heterojunction photocatalyst: a first-principle study.

In this study, density functional theory and hybrid functional theory are used to calculate the work function and energy band structure of MoS2 and WSe2, as well as the binding energy, work function, energy band structure, density of states, charge density difference, energy band alignment, Bader charge, and H adsorption free energy of MoS2/WSe2. The difference in work function led to the formation of a built-in electric field from WSe2 to MoS2, and the energy band alignment indicated that the redox reactions were located on the MoS2 and WSe2 semiconductors, respectively. The binding energy of MoS2 and WSe2 indicated that the thermodynamic properties of the heterogeneous structure were stable. MoS2 and WSe2 gathered electrons and holes, respectively, and redistributed them under the action of the built-in electric field. The photogenerated electrons and holes were enriched on the surface of WSe2 and MoS2, which greatly improved the efficiency of hydrogen production by photocatalytic water splitting.

Photocatalytic properties and energy band offset of a tungsten disulfide/graphitic carbon nitride van der Waals heterojunction.

Semiconductor heterojunctions have higher photocatalytic performance than a single photocatalytic material. However, the energy band offset and the photocatalytic reaction mechanism of these heterojunctions remain controversial. Here, tungsten disulfide (WS2)/graphitic carbon nitride (GCN) heterojunction photocatalytic water splitting is investigated with the hybrid density functional method. The band structures and the density of states (DOS) indicate that the WS2/GCN heterojunction is a type-II heterojunction, and its valence band offset and conduction band offset are 0.27 and 0.04 eV, respectively. The differential charge density distribution and the work function calculation indicate that a built-in electric field is formed in the WS2/GCN heterojunction. The potential of the built-in electric field is 0.16 V, and its direction is from the GCN surface to the WS2 surface. The built-in electric field separates the photogenerated electrons and the holes in space, effectively improving the photocatalytic efficiency of the WS2/GCN heterojunction. Our work provides insights into the electronic properties and the photocatalytic hydrogen evolution mechanism of the WS2/GCN heterojunction.

Synthesis of novel tetrazine based D-π-A organic dyes for photoelectrochemical and photocatalytic hydrogen evolution

Two novel donor-π-acceptor (D-π-A) dyes, called as MK-2 and MK-8, are synthesized. Their structural, optical and electrochemical properties are investigated by NMR, absorption/photoluminescence spectroscopies and cyclic voltammetry techniques, respectively. Photocatalytic and photoelectrochemical hydrogen evolution properties of these D-π-A dyes are explored by using triethanolamine (TEOA) as a sacrificial electron donor under anaerobic conditions and visible light irradiation with or without co-catalysts (Cu2WS4 and Pt) for the first time. Photoelectrochemical and photocatalytic hydrogen evolution reaction (HER) activities of these dyes are studied by using TiO2 coated FTO electrodes and powdered TiO2 (Degussa P25), respectively. Photoelectrochemical response of MK-2/TiO2 and MK-8/TiO2 are figured out in the order of 180 μA cm−1 and 80 μA cm−1. The photocatalytic hydrogen evolution amounts of MK-2/TiO2, MK-2/TiO2/Cu2WS4, MK-2/TiO2/Pt, MK-8/TiO2, MK-8/TiO2/Cu2WS4 and MK-8/TiO2/Pt are turned out to be 565, 920, 1828, 374, 522 and 1260 μmolg−1h−1, respectively. Dye/TiO2 photocatalysts are displayed good stability in the both photochemical HER experiments. The alteration in the HER activities of MK-2 and MK-8 is explained by molecule structures of dyes. The proposed mechanism of photocatalytic hydrogen evolution is clarified by using electrochemical band levels of each constituent.

Stress corrosion cracking behavior of rusted X100 steel under the combined action of Cl− and HSO3− in a wet–dry cycle environment

X100 steel is an important material used to construct marine pipelines; hence, understanding its stress corrosion cracking (SCC) behavior is important. Herein, we investigated the SCC mechanism of rusted X100 steel in a wet–dry cycle environment at various Cl− and HSO3− contents. Slow strain-rate testing revealed brittle fracture features at high HSO3− content, while electrochemical studies showed that HSO3− promotes increased cathode current density that contributes to stress corrosion cracking. We conclude that SCC cracking is initiated at pits formed by anodic dissolution, while the hydrogen-evolution mechanism dominates in a high HSO3− concentration environment.

Control of the substituent at the nitrogen atom in a 2,4,6-triphenylpyridinium perchlorates tunes the electrocatalytic hydrogen evolution mechanism and efficiency

Electrochemical properties and electrocatalytic activity in of hydrogen evolution reaction (HER) in new members of the family of homogeneous organic metal-free catalysts based on N-methyl and N-phenyl - 2,4,6-triphenylpyridinium perchlorates were studied using electrochemical methods. With a similar structure and electrochemical properties, the electrocatalytic behavior differs dramatically. The main reason for this is the “nature” of the substituent in the nitrogen atom. It is shown for the first time that by varying the potential of the electrocatalytic process, it is possible to control the mechanism (switch) and the efficiency of the process. Foot-of-the-wave analysis (FOWA) was performed to measure the kinetics of the process. The calculated value of kobs = 155.2 s−1 for N-methyl-2,4,6-triphenylpyridinium perchlorate is a record among all homogeneous metal-free electrocatalysts.

Molecular Control of Heterogeneous Electrocatalysis through Graphite Conjugation.

The efficient interconversion of electrical and chemical energy requires catalysts capable of accelerating multielectron reactions at or near electrified interfaces. These reactions can be performed at metallic surface sites on heterogeneous electrocatalysts or through redox mediation at molecular electrocatalysts. The relative ease of synthesis and characterization for homogeneous catalysts has allowed for molecular-level control over the active site and permitted systematic tuning of activity and selectivity. Similar control is difficult to achieve with heterogeneous electrocatalysts, because they typically exhibit a distribution of active site geometries and local electronic structures, which are challenging to modify with molecular precision. However, metallic heterogeneous electrocatalysts benefit from a continuum of electronic states that distribute the redox burden of multielectron transformations, enabling more efficient catalysis. We envisioned that we could combine the attractive properties of molecular and heterogeneous catalysts by integrating tunable molecular active sites into the delocalized band states of a conductive solid. The Surendranath group has developed a class of electrocatalysts in which molecules are strongly electronically coupled to graphitic electrodes through a conductive, aromatic pyrazine linkage such that they behave like metallic surface active sites. In this Account, we discuss the dual role of these graphite-conjugated catalysts (GCCs) as a platform with which to answer molecular-level questions of metallic active sites and as a tool with which to fundamentally alter the mechanism and enhance the performance of molecular active sites. We begin by describing the electrochemical and spectroscopic studies that demonstrated that GCC sites behave like metallic active sites rather than simply as redox mediators attached to electrode surfaces. We then discuss how electrochemical studies of a series of graphite-conjugated acids enabled the construction of a molecular model for the thermochemistry of proton-coupled electron transfer reactions at GCC sites based on the pKa of the molecular analogue of the conjugated site and the potential of zero free charge of the electrode. In the final section, we discuss the effects of graphite conjugation on the mechanism and rate of oxygen reduction, hydrogen evolution, and carbon dioxide reduction catalysis across four different GCC platforms involving N-heterocycle, organometallic, and metalloporphyrin active sites. We discuss how molecular-level tuning at graphite-conjugated active sites directly correlates to changes in catalytic activity for the oxygen reduction reaction. We demonstrate that graphite-conjugated porphyrins show enhanced catalytic oxygen reduction activity over amide-linked porphyrins. Lastly, we describe how catalysis at graphite-conjugated sites proceeds through mechanisms involving concerted electron transfer and substrate activation, in stark contrast to the mechanisms observed for molecular analogues. Overall, we showcase how GCCs provide a rich platform for controlling heterogeneous catalysis at the molecular level.

Water splitting catalysis beginning with FeCo2S4@Ni(OH)2: Investigation of the true catalyst with favorable stability

Highly active and earth-abundant dual functional electrocatalyst have been developed to resolve energy conversion and storage from water splitting. Herein, for the first time, synthesis of morphology-controllable for the electrocatalytic active Ni(OH)2 nanosheets deposited on the periphery of FeCo2S4 nanorods on the porous nickel foams was designed through two step hydrothermal process. For water splitting, FeCo2S4@Ni(OH)2/NF-3h//FeCo2S4@Ni(OH)2/NF-3h required cell voltage of 1.52 V to drive 20 mA cm−2, which is one of the smallest value reported compared with previous literature for electrochemistry water splitting through a large number of literature research. Density functional theory calculations and experimental characterization are done to calculate the surface adsorption energy of water molecules on the catalyst surface and explore the hydrogen evolution mechanism of synergistic catalysis. What is noteworthy is that FeCo2S4@Ni(OH)2/NF-3h remain a current intensity of 15 mA cm−2 for 140 h in 1.0 M KOH solution with a slight increment of the overpotential.