Crystalline Phase Engineering to Modulate the Interfacial Interaction of the Ruthenium/Molybdenum Carbide for Acidic Hydrogen Evolution.

Ruthenium (Ru) is an ideal substitute to commercial Pt/C for the acidic hydrogen evolution reaction (HER), but it still suffers from undesirable activity due to the strong adsorption free energy of H* (ΔGH*). Herein, we propose crystalline phase engineering by loading Ru clusters on precisely prepared cubic and hexagonal molybdenum carbide (α-MoC/ß-Mo2C) supports to modulate the interfacial interactions and achieve high HER activity. Advanced spectroscopies demonstrate that Ru on ß-Mo2C shows a lower valence state and withdraws more electrons from the support than that of Ru on α-MoC, indicative of a strong interfacial interaction. Density functional theory reveals that the ΔGH* of Ru/ß-Mo2C approaches 0 eV, illuminating an enhancement mechanism at the Ru/ß-Mo2C interface. The resultant Ru/ß-Mo2C exhibits an encouraging performance in a proton exchange membrane water electrolyzer with a low cell voltage (1.58 V@ 1.0 A cm-2) and long stability (500 h@ 1.0 A cm-2).

Second-Shell N Dopants Regulate Acidic O2 Reduction Pathways on Isolated Pt Sites.

Pt is a well-known benchmark catalyst in the acidic oxygen reduction reaction (ORR) that drives electrochemical O2-to-H2O conversion with maximum chemical energy-to-electricity efficiency. Once dispersing bulk Pt into isolated single atoms, however, the preferential ORR pathway remains a long-standing controversy due to their complex local coordination environment and diverse site density over substrates. Herein, using a set of carbon nanotube supported Pt-N-C single-atom catalysts, we demonstrate how the neighboring N dopants regulate the electronic structure of the Pt central atom and thus steer the ORR selectivity; that is, the O2-to-H2O2 conversion selectivity can be tailored from 10% to 85% at 0.3 V versus reversible hydrogen electrode. Moreover, via a comprehensive X-ray-radiated spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy analysis coupled with theoretical modeling, we reveal that a dominant pyridinic- and pyrrolic-N coordination within the first shell of Pt-N-C motifs favors the 4e- ORR, whereas the introduction of a second-shell graphitic-N dopant weakens *OOH binding on neighboring Pt sites and gives rise to a dominant 2e- ORR. These findings underscore the importance of the chemical environment effect for steering the electrochemical performance of single-atom catalysts.

Oxygen Functional Groups Regulate Cobalt-Porphyrin Molecular Electrocatalyst for Acidic H2O2 Electrosynthesis at Industrial-Level Current.

Electrosynthesis of hydrogen peroxide (H2O2) based on proton exchange membrane (PEM) reactor represents a promising approach to industrial-level H2O2 production, while it is hampered by the lack of high-efficiency electrocatalysts in acidic medium. Herein, we present a strategy for the specific oxygen functional group (OFG) regulation to promote the H2O2 selectivity up to 92% in acid on cobalt-porphyrin molecular assembled with reduced graphene oxide. In-situ X-ray adsorption spectroscopy, in-situ Raman spectroscopy and Kelvin probe force microscopy combined with theoretical calculation unravel that different OFGs exert distinctive regulation effects on the electronic structure of Co center through either remote (carboxyl and epoxy) or vicinal (hydroxyl) interaction manners, thus leading to the opposite influences on the promotion in 2e- ORR selectivity. As a consequence, the PEM electrolyzer integrated with the optimized catalyst can continuously and stably produce the high-concentration of ca. 7 wt% pure H2O2 aqueous solution at 400 mA cm-2 over 200 h with a cell voltage as low as ca. 2.1 V, suggesting the application potential in industrial-scale H2O2 electrosynthesis.

Overall Design of Anode with Gradient Ordered Structure with Low Iridium Loading for Proton Exchange Membrane Water Electrolysis.

Insufficient catalyst utilization, limited mass transport, and high ohmic resistance of the conventional membrane electrode assembly (MEA) lead to significant performance losses of proton exchange membrane water electrolysis (PEMWE). Herein we propose a novel ordered MEA based on anode with a 3D membrane/catalytic layer (CL) interface and gradient tapered arrays by the nanoimprinting method, confirmed by energy dispersive spectroscopy. Benefiting from the maximized triple-phase interface, rapid mass transport, and gradient CL by overall design, such an ordered structure with Ir loading of 0.2 mg cm-2 not only greatly increases the electrochemical active area by 4.2 times but also decreases the overpotentials of both mass transport and ohmic polarization by 13.9% and 8.7%, respectively, compared with conventional MEA with an Ir loading of 2 mg cm-2, thus ensuring a superior performance (1.801 V at 2 A cm-2) and good stability. This work provides a new strategy of designing MEA for high-performance PEMWE.