Mo2 C-Based Ceramic Electrode with High Stability and Catalytic Activity for Hydrogen Evolution Reaction at High Current Density.

Developing robust electrodes with high catalytic performance is a key step for expanding practical HER (hydrogen evolution reaction) applications. This paper reports on novel porous Mo2 C-based ceramics with oriented finger-like holes directly used as self-supported HER electrodes. Due to the suitable MoO3 sintering additive, high-strength (55 ± 6 MPa) ceramic substrates and a highly active catalytic layer are produced in one step. The in situ reaction between MoO3 and Mo2 C enabled the introduction of O in the Mo2 C crystal lattice and the formation of Mo2 C(O)/MoO2 heterostructures. The optimal Mo2 C-based electrode displayed an overpotential of 333 and 212 mV at 70 °C under a high current intensity of 1500 mA cm-2 in 0.5 m H2 SO4 and 1.0 m KOH, respectively, which are markedly better than the performance of Pt wire electrode; furthermore, its price is three orders of magnitude lower than Pt. The chronopotentiometric curves recorded in the 50 - 1500 mA cm-2 range, confirmed its excellent long-term stability in acidic and alkaline media for more than 260 h. Density functional theory (DFT) calculations showed that the Mo2 C(O)/MoO2 heterostructures has an optimum electronic structure with appropriate *H adsorption-free energy in an acidic medium and minimum water dissociation energy barrier in an alkaline medium.

Incorporation of Sequence Aza-Substitution and Thiophene Bridge in Linear Conjugated Polymers Toward Highly Efficient Photo-Catalytic Hydrogen Evolution.

The hydrogen evolution performance of organic photo-catalysts is lagged by numerous factors, such as the narrow photon absorption window, low charge transport, and so on. In this paper, four linear conjugated polymers are designed and synthesized based on dibenzothiophene-S,S-dioxide as an acceptor, and aza-substituted thiophene-phenyl-thiophene with different substitution numbers as co-units. The polymers with the thiophene bridge and aza-substitution exhibit broad visible absorption because of the extended conjugated length and improved planar structures resulting from the intramolecular non-covalent interactions (S···N or CH···N). The mono-substitution polymer without the addition of any co-catalysts shows the highest photo-catalytic performances with the hydrogen evolution rates of 8950 and 7388 µmol g-1 h-1 under the UV-vis (>295 nm) and visible (>420 nm) irradiation, respectively. The corresponding apparent quantum yields are as high as 8.34, 5.37, and 1.96% for the 420, 500, and 550 nm monochromatic light irradiation, respectively, which are much higher than those of the classic polymer (P7) without thiophene bridge and aza-substitution. This work indicats that the incorporation of thiophene bridge enhances visible absorption and aza-substitution optimized co-planarity and activate reactive sites, which should be an effective strategy to improve the photo-catalytic performance of linear conjugated polymers.

Robust Porous WC-Based Self-Supported Ceramic Electrodes for High Current Density Hydrogen Evolution Reaction.

Developing an economical, durable, and efficient electrode that performs well at high current densities and is capable of satisfying large-scale electrochemical hydrogen production is highly demanded. A self-supported electrocatalytic "Pt-like" WC porous electrode with open finger-like holes is produced through industrial processes, and a tightly bonded nitrogen-doped WC/W (WC-N/W) heterostructure is formed in situ on the WC grains. The obtained WC-N/W electrode manifests excellent durability and stability under multi-step current density in the range of 30-1000 mA cm-2 for more than 220 h in both acidic and alkaline media. Although WC is three orders of magnitude cheaper than Pt, the produced electrode demonstrates comparable hydrogen evolution reaction performance to the Pt electrode at high current density. Density functional theory calculations attribute its superior performance to the electrode structure and the modulated electronic structure at the WC-N/W interface.