We report a facile synthetic protocol to prepare mesoporous FeS without the aid of hard template as an electrocatalyst for the hydrogen evolution reaction (HER). The mesoporous FeS materials with high surface area were successfully prepared by a sol-gel method following a sulfurization treatment in an HS atmosphere. A remarkable HER catalytic performance was achieved with a low overpotential of 96 mV at a current density of 10 mA·cm and a Tafel slope of 78 mV per decade under alkaline conditions (pH 13). The theoretical calculations indicate that the excellent catalytic activity of mesoporous FeS is attributed to the exposed (210) facets. The mesoporous FeS material might be a promising alternative to the Pt-based electrocatalysts for water splitting.

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Theoretical studies on M 13 (M = Fe, Co, Ni) and M 13 Pt n (for n = 3, 4, 5, 20) clusters including the spin-orbit coupling are done using density functional theory. The magnetic anisotropy energy (MAE) along with the spin and orbital moments are calculated for M 13 icosahedral clusters. The angle-dependent energy differences are modelled using an extended classical Heisenberg model with local anisotropies. From our studies, the MAE for Jahn-Teller distorted Fe 13 , Mackay distorted Fe 13 and nearly undistorted Co 13 clusters are found to be 322, 60 and 5 µeV/atom, respectively, and are large relative to the corresponding bulk values, (which are 1.4 and 1.3 µeV/atom for bcc Fe and fcc Co, respectively.) However, for Ni 13 (which practically does not show relaxation tendencies), the calculated value of MAE is found to be 0.64 µeV/atom, which is approximately four times smaller compared to the bulk fcc Ni (2.7 µeV/atom). In addition, MAE of the capped cluster (Fe 13 Pt 4 ) is enhanced compared to the uncapped Jahn-Teller distorted Fe 13 cluster.

First-principles theoretical studies enable an electronic and magnetic characterization of the recently synthesized Ni9Te6(PEt3)8C60 ionic material consisting of Ni9Te6(PEt3)8 superatoms and C60. The PEt3 ligands are shown to create an internal coulomb well that lifts the quantum states of the Ni9Te6 cluster, lowering its ionization potential to 3.39 eV thus creating a superalkali motif. The metallic core has a spin magnetic moment of 5.3 μB in agreement with experiment. The clusters are marked by low magnetic anisotropy energy (MAE) of 2.72 meV and a larger intra-exchange coupling exceeding 0.2 eV, indicating that the observed paramagnetic behavior around 10K is due to superparamagnetic relaxations. The magnetic motifs separated by C60 experience a weak superexchange that stabilizes a ferromagnetic ground state as observed around 2 K. The calculated MAE is sensitive to the charged state that could account for the observed change in magnetic transition temperature with size of the ligands or anion.

Hydrogen oxidation reaction (HOR) is one of the critical processes in clean and sustainable energy conversion devices such as anion-exchange membrane fuel cells (AEMFCs). There is significant interest in the design of highly active anode catalysts for such fuel cells. Here, we present the results of an ab initio study that explores the mechanism of HOR for palladium-ceria anode catalysts. This combination of materials has been shown to display excellent HOR performance experimentally. We use density functional theory with exchange− correlation functionals described by the generalized gradient approximation and the necessary Hubbard corrections. This allows us to accurately capture the electronic structure and the associated functional properties of all the components of the catalyst. The computations are carried out for multiple palladium concentrations on ceria surfaces. The reaction pathway for HOR is investigated via the Tafel reaction for the dissociation of hydrogen molecules and Volmer reaction for the formation of water molecules. Our findings show that palladium-ceria bifunctional systems have improved HOR activity compared to their individual components. Specifically, an enhanced catalytic activity is predicted for 10 at. % (7 wt %) palladium on ceria. We explain this behavior using multiple activity descriptors including hydrogen, OH, and H 2 O binding energies, and hybridization and charge transfer between the catalyst, the substrate, and adsorbents. The results suggest that the high HOR activity can be attributed to the delicate balance between the H and OH interactions with the palladium-ceria support as well as the interaction between the individual components that make up the heterostructure. The detailed ab initio analysis provides invaluable insights toward electronic, atomistic, and molecular mechanisms of HOR and paves the way for the development of catalysts that use significantly reduced amounts of precious metals.

Figure 7. (a) and (b) denote the hybridized dxz/yz and d z 2 orbitals, respectively.(c) The position of threedorbitals and their averagep ositionsa re showninb lue (d z 2 ), black (d xz ), green (d yz )a nd red (average positions of d xz and d yz )orbitals, respectively.(d) The E A for free (black circle), Embedded (blue circles) and adsorbed (red circles)T Ms ystems.

The electrolysis of water provides a powerful pathway for the storage and conversion of clean and renewable energy. Therefore, the development of earth-abundant, inexpensive, highly efficient electrocatalysts contributes a great deal to the overall efficiency of a water electrolytic system. Here, inspired by the low charge transfer resistance of mixed-valence cations, the favorable H atom binding energy of cobalt, and high electrical conductivity of graphene, we report a facile synthesis strategy to synthesize a spinel ternary oxide material consisting of nickel, manganese, and cobalt supported on reduced graphene oxide (rGO/NMC) with further conversion into a spinel ternary sulfide via a gaseous sulfurization protocol. The rGO/NMC-312 oxide material is found to be an efficient OER electrocatalyst with an overpotential as low as 320 mV for a current density of 10 mA cm −2 , which is comparable to that of the state of the art OER catalysts. In addition, when used as HER electrocatalysts, the as-converted rGO/ NMC-312 sulfide materials exhibit a low overpotential of 151 mV to reach a current density of 10 mA cm −2 , a small Tafel slope of 52 mV/decade, and a remarkable long-term stability. Impressively, a voltage of 1.56 V is required to achieve a current density of 20 mA cm −2 in an alkaline medium at room temperature by applying rGO/NMC-312 oxide and sulfide as an alkaline water electrolysis anode and cathode, respectively. Our work offers a strategy to apply spinel ternary oxides and sulfides as electrocatalysts in water electrolysis.

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