Reversible, carbon dioxide mediated chemical hydrogen storage was first demonstrated using a heterogeneous Pd catalyst supported on mesoporous graphitic carbon nitride (Pd/mpg-C 3 N 4 ). The Pd nanoparticles were found to be uniformly dispersed onto mpg-C 3 N 4 with an average size of 1.7 nm without any agglomeration and further exhibit superior activity for the dehydrogenation of formic acid with a turnover frequency of 144 h À1 even in the absence of external bases at room temperature. Initial DFT studies suggest that basic sites located at the mpg-C 3 N 4 support play synergetic roles in stabilizing reduced Pd nanoparticles without any surfactant as well as in initiating H 2 -release by deprotonation of formic acid, and these potential interactions were further confirmed by X-ray absorption near edge structure (XANES). Along with dehydrogenation, Pd/mpg-C 3 N 4 also proves to catalyze the regeneration of formic acid via CO 2 hydrogenation. The governing factors of CO 2 hydrogenation are further elucidated to increase the quantity of the desired formic acid with high selectivity.

For efficient water splitting, it is essential to develop inexpensive and super-efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, we report a phosphate-based electrocatalyst [Fe3Co(PO4)4@reduced-graphene-oxide(rGO)] showing outstanding OER performance (much higher than state-of-the-art Ir/C catalysts), the design of which was aided by first-principles calculations. This electrocatalyst displays low overpotential (237 mV at high current density 100 mA cm−2 in 1 M KOH), high turnover frequency (TOF: 0.54 s−1), high Faradaic efficiency (98%), and long-term durability. Its remarkable performance is ascribed to the optimal free energy for OER at Fe sites and efficient mass/charge transfer. When a Fe3Co(PO4)4@rGO anodic electrode is integrated with a Pt/C cathodic electrode, the electrolyzer requires only 1.45 V to achieve 10 mA cm−2 for whole water splitting in 1 M KOH (1.39 V in 6 M KOH), which is much smaller than commercial Ir-C//Pt-C electrocatalysts. This cost-effective powerful oxygen production material with carbon-supporting substrates offers great promise for water splitting.

Computational calculations and experimental studies reveal that the CoOOH phase and the intermediate-spin (IS) state are the key factors for realizing efficient Co-based electrocatalysts for the oxygen evolution reaction (OER). However, according to thermodynamics, general cobalt oxide converts to the CoO2 phase under OER condition, retarding the OER kinetics. Herein, we demonstrate a simple and scalable strategy to fabricate electrodes with maintaining Fe-CoOOH phase and an IS state under the OER. The changes of phase and spin states were uncovered by combining in-situ/operando X-ray based absorption spectroscopy and Raman spectroscopy. Electrochemical reconstruction of chalcogenide treated Co foam affords a highly enlarged active surface that conferred excellent catalytic activity and stability in a large-scale water electrolyzer. Our findings are meaningful in that the calculated results were experimentally verified through the operando analyses. It also proposes a new strategy for electrode fabrication and confirms the importance of real active phases and spin states under a particular reaction condition.

CuO nanoparticles (NPs), Cu 2 O/CuO and CuO/TiO 2 nanocomposites (NCs) have been synthesized by using modified co-precipitation method with three different schemes of synthesis.Crystal structure and morphology of the samples have been investigated by the synchrotron Xray diffraction and transmission electron microscopy, respectively. The detailed local electronic structure of NPs and NCs has been determined by the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) spectroscopy. O K-edge, Cu K-and Cu L-edge XANES spectra revealed the dominating +2 valence state of Cu in case of CuO NPs and CuO/TiO 2 NCs, although Cu +1 was dominated in the Cu 2 O/CuO NCs. A comparison of local atomic structure around the Cu sites revealed the shorter Cu -O bond distances in the as-synthesized samples with respect to the bulk CuO or Cu 2 O. The Ti K-edge EXAFS fittings for CuO/TiO 2 NCs revealed that the local anatase TiO 2 phase has been formed, with Ti -O bond distance of 1.98 Å. We further demonstrated that the CuO NPs, Cu 2 O/CuO and CuO/TiO 2 NCs can serve as effective photocatalyst towards the degradation of two novel water 2 pollutants, (i) methyl orange (MO) and (ii) potassium dichromate (PD), under the visible lightirradiation. It was found that the Cu 2 O/CuO NCs exhibit higher photocatalytic activity towards the degradation of MO and PD than the CuO NPs or CuO/TiO 2 NCs. The mechanism of the photodegradation of MO and PD is also discussed in terms of possible chemical reactions, along with the electronic structure and surface properties of the samples.

Electrocatalytic conversion of CO2 into value-added products offers a new paradigm for a sustainable carbon economy. For active CO2 electrolysis, the single-atom Ni catalyst has been proposed as promising from experiments, but an idealized Ni–N4 site shows an unfavorable energetics from theory, leading to many debates on the chemical nature responsible for high activity. To resolve this conundrum, here we investigated CO2 electrolysis of Ni sites with well-defined coordination, tetraphenylporphyrin (N4–TPP) and 21-oxatetraphenylporphyrin (N3O–TPP). Advanced spectroscopic and computational studies revealed that the broken ligand-field symmetry is the key for active CO2 electrolysis, which subordinates an increase in the Ni redox potential yielding NiI. Along with their importance in activity, ligand-field symmetry and strength are directly related to the stability of the Ni center. This suggests the next quest for an activity–stability map in the domain of ligand-field strength, toward a rational ligand-field engineering of single-atom Ni catalysts for efficient CO2 electrolysis.

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A new solid-state Li ion conductor composed of LiBH 4 and Al 2 O 3 was synthesized by a simple ball-milling process. The element distribution map obtained by transmission electron microscopy demonstrates that the LiBH 4 and Al 2 O 3 are well mixed and form a large interface after ballmilling. The ionic conductivity of the mixture reaches as high as 2 × 10 −4 S cm −1 at room temperature when the volume fraction of Al 2 O 3 is approximately 44%. The ionic conductivity of the interface between LiBH 4 and Al 2 O 3 was extracted by using a continuum percolation model, which turns out to be about 10 −3 S cm −1 at room temperature, being 10 5 times higher than that of pure LiBH 4 . This remarkable rise in conductivity is accompanied by the lowered activation energy for the Li ion conduction in the mixture, indicating that the interface layer facilitates Li ion conduction. Near-edge X-ray absorption fine structure analysis reveals the presence of B− O bondings in the mixture, which was not detected by X-ray diffraction. This disruption of the chemical bondings at the interface may allow an increase in carrier concentration and/or mobility thereby resulting in the pronounced enhancement in conductivity. This result provides a guideline for designing fast Li ion conductor through interface engineering.

Despite highly promising characteristics of three-dimensionally (3D) nanostructured catalysts for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWEs), universal design rules for maximizing their performance have not been explored. Here we show that woodpile (WP)-structured Ir, consisting of 3D-printed, highly-ordered Ir nanowire building blocks, improve OER mass activity markedly. The WP structure secures the electrochemically active surface area (ECSA) through enhanced utilization efficiency of the extended surface area of 3D WP catalysts. Moreover, systematic control of the 3D geometry combined with theoretical calculations and various electrochemical analyses reveals that facile transport of evolved O2 gas bubbles is an important contributor to the improved ECSA-specific activity. The 3D nanostructuring-based improvement of ECSA and ECSA-specific activity enables our well-controlled geometry to afford a 30-fold higher mass activity of the OER catalyst when used in a single-cell PEMWE than conventional nanoparticle-based catalysts.