Fe−N−C electrocatalysts have been demonstrated to be the most promising substitutes for benchmark Pt/C catalysts for the oxygen reduction reaction (ORR). Herein, we report that N‐doped carbon materials with trace amounts of iron (0–0.08 wt. %) show excellent ORR activity and durability comparable and even superior to those of Pt/C in both alkaline and acidic media without significant contribution by the metal sites. Such an N‐doped carbon (denoted as N‐HPCs) features a hollow and hierarchically porous architecture, and more importantly, a noncovalently bonded N‐deficient/N‐rich heterostructure providing the active sites for oxygen adsorption and activation owing to the efficient electron transfer between the layers. The primary Zn‐air battery using N‐HPCs as the cathode delivers a much higher power density of 158 mW cm−2, and the maximum power density in the H2−O2 fuel cell reaches 486 mW cm−2, which is comparable to and even better than those using conventional Fe−N−C catalysts at cathodes.

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Platinum (Pt) is an efficient catalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist. The strong metal-support interaction (SMSI) between the metal and carrier causes the charge transfer and mass transport from the support to the metal. Herein, Pt species (0.5 wt.%) with various particle sizes supported on carbon nanotubes (CNTs) have been synthesized by a photo-reduction method. Thẽ 1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions, and the mass activity of it is even 23-36 times that of Pt/C. While for ORR, the~3 nm-sized Pt catalyst exhibits the optimal performance, and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media, respectively. The high HER and ORR performances of the~1.5 nm-and~3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites, which is meaningful for the design of efficient electrocatalysts for renewable energy application.

Given its promising electron transportation ability, excellent electrical conductivity, and larger work function (6.2 eV) disclosed by density functional theory calculations, MXene material, O-terminated Ti 3 C 2 has the potential to serve as a perfect cocatalyst. Herein, a novel Ti 3 C 2 /SrTiO 3 heterostructure based on partly superficial oxidation from precursor multilayered Ti 3 C 2 is developed as a photocatalyst for efficiently photocatalytic reduction and removal of U(VI). Specifically, the composite of 2 wt % Ti 3 C 2 /SrTiO 3 (0.02 Ti 3 C 2 / SrTiO 3 ) exhibits an excellent photocatalytic UO 2 2+ removal rate of 77%, which is nearly 38 times higher than that of the pristine SrTiO 3 . The enhanced photocatalytic performance of 0.02 Ti 3 C 2 /SrTiO 3 is systematically identified by photoluminescence spectroscopy, UV−vis diffuse reflectance spectroscopy, Raman spectroscopy, and electrochemical characterizations. The multilayered Ti 3 C 2 as a cocatalyst can facilitate the charge transportation and inhibit the recombination of electrons in the conduction band. This work establishes the enticing potential for developing doped perovskite oxide crystals based on the MXene Ti 3 C 2 with sun-light responsivity for improving solar energy utilization.

Substituting hydrazine oxidation reaction for oxygen evolution reaction can result in greatly reduced energy consumption for hydrogen production, however, the mechanism and the electrochemical utilization rate of hydrazine oxidation reaction remain ambiguous. Herein, a bimetallic and hetero-structured phosphide catalyst has been fabricated to catalyze both hydrazine oxidation and hydrogen evolution reactions, and a new reaction path of nitrogen-nitrogen single bond breakage has been proposed and confirmed in hydrazine oxidation reaction. The high electro-catalytic performance is attributed to the instantaneous recovery of metal phosphide active site by hydrazine and the lowered energy barrier, which enable the constructed electrolyzer using bimetallic phosphide catalyst at both sides to reach 500 mA cm−2 for hydrogen production at 0.498 V, and offer an enhanced hydrazine electrochemical utilization rate of 93%. Such an electrolyzer can be powered by a bimetallic phosphide anode-equipped direct hydrazine fuel cell, achieving self-powered hydrogen production at a rate of 19.6 mol h−1 m−2.

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