Vertically-stacked W/W2C heterojunctions with high electrocatalytic capability for the hydrogen evolution reaction in a wide pH range.

The hydrogen evolution reaction (HER) in water splitting is among the foremost methods to produce clean and green hydrogen from renewable sources. The practical use of the HER technology is however hindered by the high price and/or the relatively low efficiency of the currently used catalysts. Herein, we report a heterostructured W/W2C electrocatalyst featuring vertically stacked interfaces and embedded in N-doped porous graphitic carbon (denoted as W/W2C@N-PGC) as a high-performance electrocatalyst for the HER in a wide pH range. The catalyst synthesis, accomplished through a straightforward one-pot method, is both facile and highly efficient, involving freeze-drying a suspension of the starting materials followed by pyrolyzing the obtained dry gel. Density functional theory calculations revealed the crucial role of the W/W2C heterojunction in promoting the two key steps of the HER, viz. HOH bond scission and H2 emission. Electrochemical data confirmed the excellent electrocatalytic capability of W/W2C@N-PGC toward the HER process in a wide pH range including alkaline, acidic, and neutral electrolytes. In 1.0 M KOH, we measured a low overpotential of 102 mV to drive a current density of 10 mA cm-2; a long-term stability (up to 24 h) was also realized. The data presented in this work highlight the importance of electrocatalysts with heterojunctions for the HER and the methodology presented in this work may be extended to other contemporary energy-related technologies such as CO2 reduction, oxygen evolution, and oxygen reduction reactions.

P-Doping a Porous Carbon Host Promotes the Lithium Storage Performance of Red Phosphorus.

Red phosphorus (RP) is a promising anode material for use in lithium-ion batteries (LIBs) due to its high theoretical specific capacity (2596 mA h g-1). However, the practical use of RP-based anodes has been challenged by the material's low intrinsic electrical conductivity and poor structural stability during lithiation. Here, we describe a phosphorus-doped porous carbon (P-PC) and disclose how the dopant improves the Li storage performance of RP that was incorporated into the P-PC (designated as RP@P-PC). P-doping porous carbon was achieved using an in situ method wherein the heteroatom was added as the porous carbon was being formed. The phosphorus dopant effectively improves the interfacial properties of the carbon matrix as subsequent RP infusion results in high loadings, small particle sizes, and uniform distribution. In half-cells, an RP@P-PC composite was found to exhibit outstanding performance in terms of the ability to store and utilize Li. The device delivered a high specific capacitance and rate capability (1848 and 1111 mA h g-1 at 0.1 and 10.0 A g-1, respectively) as well as excellent cycling stability (1022 mA h g-1 after 800 cycles at 2.0 A g-1). Exceptional performance metrics were also measured when the RP@P-PC was used as an anode material in full cells that contained lithium iron phosphate as the cathode material. The methodology described can be extended to the preparation of other P-doped carbon materials that are employed in contemporary energy storage applications.

Nonstoichiometric Scandium Oxide Hybridized in N-Doped Porous Graphitic Carbon Promotes the Rate Capability of Lithium-Sulfur Batteries.

Nonstoichiometric compounds are widely used in contemporary energy technologies due to their high surface polarity, tailored electronic structure, high electrical conductivity, and other enhanced properties. However, the preparation of such nonstoichiometric compounds can be complicated and, in some cases, uncontrollable and dangerous. Here, we report a "one-pot" strategy for synthesizing N-doped porous graphitic carbon that is hybridized with nonstoichiometric scandium oxide (denoted as ScO0.95@N-PGC) and show that the composite significantly promotes sulfur cathode kinetics in lithium-sulfur (Li-S) batteries. The synthesis of the ScO0.95@N-PGC composite entails heating a porous dry gel that consists of a C source (glucose), a N source (dicyandiamide), and a Sc source (Sc(NO3)3·H2O). Thermally decomposing the dicyandiamide creates a highly reductive atmosphere that simultaneously affords the hypoxic state of the ScO0.95 and dopes the carbon matrix with nitrogen. Density functional theory reveals the presence of oxygen vacancies that enable the ScO0.95 crystals to function as excellent electrical conductors, exhibit enhanced adsorption toward polysulfides, and accelerate the cathode reactions by lowering the corresponding activation energies. Moreover, Li-S cells prepared from the ScO0.95@N-PGC composite display a high specific capacity (1046 mA h g-1 at 0.5 C), an outstanding cycling stability (641 mA h g-1 after 1000 charge-discharge cycles at 0.5 C, a capacity decay of 0.038% per cycle), and a particularly outstanding rate capability (438 mA h g-1 at 8 C). The methodology described establishes a sustainable approach for synthesizing nonstoichiometric compounds while broadening their potential utility in a broad range of energy technologies.