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Producing molecular hydrogen (H2) using water provides a sustainable approach for developing clean energy technologies. Herein, we report highly active ruthenium (Ru) clusters supported on iron oxide (Ru/Fe3O4) and Fe3O4/multi-walled carbon nanotubes (Ru/Fe3O4/MWCNTs) by simple electrochemical deposition in a neutral aqueous medium. The supported catalyst exhibits good hydrogen evolution reaction (HER) activity in an acidic environment. Cyclic voltammograms (CVs) of potassium ferrocyanide (K4[Fe(CN)6]) confirm that MWCNTs enhance the electron transfer process by decreasing the redox formal potential. The overpotentials of Ru/Fe3O4/MWCNTs and Ru/Fe3O4 electrocatalysts versus the reversible hydrogen electrode (RHE) were found to be 101 mV and 306 mV to reach a current density of 10 mA cm−2. As prepared, the catalyst displays good stability and retain its HER activity even after 1000 cycles. Furthermore, the stability of Ru/Fe3O4/MWCNTs was studied using the chronopotentiometric (CP) technique for 12 h and found negligible loss in the catalytic activity towards the HER. To explore the role of Ru and underneath MWCNTs in improving the catalytic performance of Fe3O4, density functional theory (DFT) calculations were carried out. DFT calculations indicate that the octahedral site of Ru/Fe3O4 favors the HER with a low overpotential. However, Ru/Fe3O4/MWCNTs are more efficient towards the HER, which could be due to the availability of both octahedral and tetrahedral catalytic sites. [ABSTRACT FROM AUTHOR]

In this work, we report a cost-effective electro-catalyst for oxygen reduction reaction (ORR) by developing a composite between graphene oxide and carbon nanotubes and simultaneously doping with a nitrogen atom. The nitrogendoped carbon nanotube/graphene oxide composites were prepared by chemical oxidation method followed by annealing process. Such composite enhances the active adsorption sites, electrical conductivity and corrosion resistance leading to better impact toward ORR. The N-graphene oxide/functionalized carbon nanotube catalyst that furnishes both pyridinic-N and pyridinic-N-O (or oxidic-N) shows higher efficiency toward electrocatalytic ORR performance in alkaline conditions. More interestingly, as-prepared electrocatalyst shows durability test up to 20 000 potential cycles without loss in its half-wave potential (Ehalf) while commercial Pt/C catalyst shows a huge loss in Ehalf value under similar conditions, indicating sustainability in the performance of former, especially compared to the reported metal or metal-free electrocatalysts. The origin of high catalytic activity of oxidic-N is correlated with π-electron density at the Fermi level studied by density functional theory and considered as an electronic descriptor. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) by electrochemical water splitting is one of the most active areas of energy research, yet the benchmark electrocatalysts used for this reaction are based on expensive noble metals. This is a major bottleneck for their large‐scale operation. Thus, development of efficient metal‐free electrocatalysts is of paramount importance for sustainable and economical production of the renewable fuel hydrogen by water splitting. Covalent organic frameworks (COFs) show much promise for this application by virtue of their architectural stability, nanoporosity, abundant active sites located periodically throughout the framework, and high electronic conductivity due to extended π‐delocalization. This study concerns a new COF material, C6‐TRZ‐TFP, which is synthesized by solvothermal polycondensation of 2‐hydroxybenzene‐1,3,5‐tricarbaldehyde (TFP) and 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tris[(1,1′‐biphenyl)‐4‐amine]. C6‐TRZ‐TFP displayed excellent HER activity in electrochemical water splitting, with a very low overpotential of 200 mV and specific activity of 0.2831 mA cm−2 together with high retention of catalytic activity after a long duration of electrocatalysis in 0.5 m aqueous H2SO4. Density functional theory calculations suggest that the electron‐deficient carbon sites near the π electron‐donating nitrogen atoms are more active towards HER than those near the electron‐withdrawing nitrogen and oxygen atoms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Heteroatoms (B, N) doping to switch the CO oxidation mechanism from ER to LH. • A screening criterion is defined to get an efficient catalyst for CO oxidation. • 3B edge doped AGNR is identify as an active catalyst following LH mechanism. • Sabatier activity and TOF values of 0.90 and 2.47, respectively. In heterogeneous catalysis, the LH (Langmuir Hinshelwood) mechanism is more efficient and recommended over any other mechanism adopted for CO oxidation. However, the LH mechanism over a carbon surface is a challenge and is paused to be applied to any carbon surface in practical application. In this work, we carried out density functional theory to study how the incorporation of nitrogen, boron atom (C→N, C→B) and co-doping on graphene nanoribbons can modify the catalytic activity of the surface and the preference between ER (Eley-Ridel) and LH mechanism is explored. Boron plays a crucial role in the adsorption of both CO and O 2 , whereas nitrogen doping can only activate O 2 molecule through altering the triplet ground state. Considering the activation energy for the first CO 2 formation and CO binding strength, we have defined a window to identify the operation of the LH mechanism in the catalysis. 3B edge doped AGNR (armchair graphene nanoribbon doped with three boron atoms at its edge) is identified as an active catalyst for the CO oxidation through the LH mechanism, with the SA (Sabatier activity) and TOF (turnover frequency) values of 0.90 and 2.47, respectively. This approach will help to search for metal-free catalysts for the CO oxidation with the efficient LH mechanism. [ABSTRACT FROM AUTHOR]

Dioxygen adsorption and activation on metal-ligand systems are the key elements for biological oxidative metabolisms and also catalyst design for the oxygen reduction reaction (ORR). We show, through first-principles calculations, that similar dioxygen adducts can form on metal-free n -type doped hexagonal boron nitride ( h-BN ) nanostructures. The density of electron donors determines the charge state of dioxygen, either in superoxo and peroxo, which exactly correlates with the ‘end-on’ and ‘side-on’ configurations, respectively. Activated O 2 in the superoxo state shows a better catalytic performance possibly mediating the direct four-electron reduction. The formation of hydrogen peroxide (H 2 O 2 ) is practically eliminated, and thus we suggest that a surface coated with the n -type doped h-BN can be the basis for an ORR catalyst with increased stability. [ABSTRACT FROM AUTHOR]

The electrocatalytic activity of T6[100] surface containing both sp 3 (C 1 ) and sp 2 (C 2 ) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C 1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C 2 atom. This is attributed to the presence of dangling σ bond in the corresponding C 1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C 2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C 1 is considered as the active site and the final step i.e desorption of final OH − ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp 2 (maintains the high metallicity needed to reduce ohmic loss) and sp 3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR. [ABSTRACT FROM AUTHOR]

Development of an inexpensive electrocatalyst for hydrogen evolution (HER) and oxygen evolution reactions (OER) receives much traction recently. Herein, we report a facile one-pot ethyleneglycol (EG) mediated solvothermal synthesis of orthorhombic Co 2 P with particle size ~20–30 nm as an efficient HER and OER catalysts. Synthesis parameters like various solvents, temperatures, precursors ratios, and reaction time influences the formation of phase pure Co 2 P. Investigation of Co 2 P as an electrocatalyst for HER in acidic (0.5 M H 2 SO 4) and alkaline medium (1.0 M KOH), furnishes low overpotential of 178 mV and 190 mV, respectively to achieve a 10 mA cm−2 current density with a long term stability and durability. As an OER catalyst in 1.0 M KOH, Co 2 P shows an overpotential of 364 mV at 10 mA cm−2 current density. Investigation of Co 2 P NP by XPS analysis after OER stability test under alkaline medium confirms the formation of amorphous cobalt oxyhydroxide (CoOOH) as an intermediate during OER process. [Display omitted] • Co 2 P nanoparticles synthesized by one step solvothermal method. • HRTEM confirms the formation of nanoparticles with ~20–30 nm in size. • The Co 2 P catalyst exhibits high catalytic activity for HER and OER. • Co 2 P electrode shows excellent stability and durability during HER and OER. [ABSTRACT FROM AUTHOR]

Using state-of-the-art density functional theory (DFT) based approach; we investigated the catalytic activity of electron doped C 2 N monolayer (O → N) for CO oxidation. Large surface-to-volume ratio and uniformly distributed holes of recently synthesized planar 2D C 2 N have made it a potential candidate as noble metal-free catalyst. However, pristine C 2 N monolayer is chemically inert and hinders the adsorption of O 2 and CO molecule on it. Oxygen doping in C 2 N brings additional electrons to the system and introduces donor state below E F . Thus the reactivity of O-doped C 2 N (2OC 2 N) monolayer gets significantly enhanced, thereby opening up the possibility of its usage as a catalyst. This reactive 2OC 2 N surface adsorbs an incoming O 2 molecule along with the elongation of O O bond, making it chemically active. Presence of this pre-adsorbed active O 2 greatly impedes the adsorption of another incoming CO, favoring Eiley-Rideal (ER) mechanism for CO oxidation. [ABSTRACT FROM AUTHOR]

• Third reaction step (ΔG OOH -ΔG O) proposed to define the catalytic activity for OER. • Role of Oxygen intermediate is identified. • Simple and general electronic descriptor is identified. • Predictive models are developed using machine learning algorithms. Descriptor based model can be efficient in identifying an optimal carbon-based catalyst for oxygen evolution reaction (OER). Here, we correlate the O-atom adsorption strength with the OER activity of graphene nanoribbon systems and define the energy parameters (ΔG O -ΔG OH) to identify the overpotential (ɳ). The π electron based descriptor can predict the catalytic activity of the graphene surfaces. Machine learning algorithms like Multiple Linear Regression, Random Forest Regression and Support Vector Regression (SVR) are trained on the data generated by density functional theory to predict the overpotential. An optimal active site for OER using proposed SVR model is identified with overpotential (0.29 V) and then validate through DFT calculations. To generalize the study, we used SVR model on N doped GNR to predict the site-specific activity towards OER. Such a combined approach can be extended to estimate the site-specific OER activity of different carbon catalysts at a dramatically reduced computational cost. [ABSTRACT FROM AUTHOR]

• A unique site dependent descriptor is defined to express the origin of catalytic activity. • Solution to lower the CO poisoning and enhance the catalytic activity of Pt based catalyst. • Competition between the different configurations of O 2 and O as intermediates. • The role of back-donation in the binding strength of CO. The design of stable, highly active heterogeneous nanocatalyst with no CO poisoning is a challenge for the catalytic converter industry. This can be achieved by defining electronic descriptor and by understanding the bonding mechanism. We present results using density functional theory to design optimal metal nanoalloy catalysts for CO oxidation. The adsorption configuration of O 2 and O on different active sites is studied in detail to find the efficient reaction pathway for CO oxidation. The varying extent of back-donation of charge is found to be the factor deciding the CO tolerance. The trade-off between the activity and CO tolerance signifies that there is an upper limit for alloying Pt with Ni and Co. An electronic descriptor based on the occupancy of the d orbital and d band center of the host atom is defined to explain the site dependent activity of nanocatalysts. The role of underneath carbon surface on the CO oxidation activity of metal sites and CO poisoning is described. [ABSTRACT FROM AUTHOR]