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Tantalum oxynitride (TaOxN1−x) fibers were synthesized and evaluated for their electrocatalytic hydrogen activity using an in‐house developed centrifugal spinning setup. By tailoring the composition of the spinning solution and optimizing collector distance and rotation speed of the spinneret, bead‐free TaOxN1−x fibers with a diameter of 800 nm were obtained. The fibers were structurally characterized through phase and elemental analysis, confirming the formation of monoclinic TaOxN1−x with clear splitting of the X‐ray photoelectron spectroscopy peaks indicating Ta was in +5 oxidation state. The resulting oxynitride fibers exhibited superior electrocatalytic performance with low overpotentials (250 mV) to generate 10 mA/cm2 compared to Ta2O5 oxide fibers. Interestingly, the enhanced activity of oxynitride fibers was observed to be suppressed in basic medium due to the high oxophilicity of tantalum ions and a negative Gibbs adsorption‐free energy, leading to poisoning of the active sites. This work demonstrates a facile pathway for the fabrication of high‐performance electrocatalysts, based on TaOxN1−x fibers, from a cost‐effective and energy‐efficient centrifugal spinning technique. [ABSTRACT FROM AUTHOR]

Highlights: Inducing a localized crystalline iron pyrophosphate in amorphous iron phosphate overlayer. Enhanced photoelectrochemical water oxidation activity with long-term durability. The heterogeneous hybrid structure overcoming the energy barrier in water oxidation. A rational regulation of the solar water splitting reaction pathway by adjusting the surface composition and phase structure of catalysts is a substantial approach to ameliorate the sluggish reaction kinetics and improve the energy conversion efficiency. In this study, we demonstrate a nanocrystalline iron pyrophosphate (Fe4(P2O7)3, FePy)-regulated hybrid overlayer with amorphous iron phosphate (FePO4, FePi) on the surface of metal oxide nanostructure with boosted photoelectrochemical (PEC) water oxidation. By manipulating the facile electrochemical surface treatment followed by the phosphating process, nanocrystalline FePy is localized in the FePi amorphous overlayer to form a heterogeneous hybrid structure. The FePy-regulated hybrid overlayer (FePy@FePi) results in significantly enhanced PEC performance with long-term durability. Compared with the homogeneous FePi amorphous overlayer, FePy@FePi can improve the charge transfer efficiency more significantly, from 60% of FePi to 79% of FePy@FePi. Our density-functional theory calculations reveal that the coexistence of FePi and FePy phases on the surface of metal oxide results in much better oxygen evolution reaction kinetics, where the FePi was found to have a typical down-hill reaction for the conversion from OH* to O2, while FePy has a low free energy for the formation of OH*. [ABSTRACT FROM AUTHOR]

A versatile use of a sulfur self‐doped biochar derived from Camellia japonica (camellia) flowers is demonstrated as a multifunctional catalyst for overall water splitting and a supercapacitor. The native sulfur content in the camellia flower facilitates in situ self‐doping of sulfur, which highly activates the camellia‐driven biochar (SA‐Came) as a multifunctional catalyst with the enhanced electron‐transfer ability and long‐term durability. For water splitting, an SA‐Came‐based electrode is highly stable and shows reaction activities in both hydrogen and oxygen evolution reactions, with overpotentials of 154 and 362 mV at 10 mA cm−2, respectively. For supercapacitors, SA‐Came achieves a specific capacitance of 125.42 F g−1 at 2 A g−1 and high cyclic stability in a three‐electrode system in a 1 M KOH electrolyte. It demonstrated a high energy density of 34.54 Wh kg−1 at a power density of 1600 W kg−1 as a symmetric hybrid supercapacitor device with a wide working potential range of 0–1.6 V. [ABSTRACT FROM AUTHOR]

Summary: The roles of amorphous phases in photochemical water splitting of semiconductors are still in debate, as the effects of the amorphous phase are largely irregular even in a single material. We presumed that the photochemistry of crystal‐amorphous mixed semiconductor systems would be governed by the interface characteristics, and conducted a systematic study to understand the origins of the largely varying photochemical reaction of semiconductors having an amorphous phase. First‐principles calculations on crystalline anatase and amorphous TiO2 showed that the coexistence of crystalline and amorphous TiO2 and the exposure of the phase boundary are advantageous due to the accelerated charge separation by interface dipole moment and the parallelizable oxygen evolution reaction at the boundary. Our computation‐based strategies were demonstrated in our experiments: only the TiO2 nanoparticle and nanotube having partial amorphization on surfaces have highly enhanced photocatalytic water splitting performances (approximately 700%) compared to the pristine and completely amorphized TiO2 systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D/2D heterostructure of two well-defined carbon matrices. • Interfacial activity of the g-C 3 N 4 film on the rGO layer. • Modified electronic states on the interface for superior OER and HER activity. • DFT simulation on the plane-averaged charge density difference. • Resolving the local pH reduction problem and electron transport. To increase the productivity of hydrogen and oxygen generation, the carbon-based electrocatalyst with 2D/2D structure, graphitic carbon nitride with reduced graphene oxide (g-C 3 N 4 /rGO), was synthesized via a facile electrostatic self-assembly method and was used as electrocatalyst for full water-splitting. In the alkaline electrolyte, g-C 3 N 4 /rGO showed lower overpotential and Tafel slope of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, than the other 2D structured materials. The DFT calculation simulates the spontaneous electron transfer, low charge transfer resistance, and internal electric field of g-C 3 N 4 /rGO electrocatalysts. Especially, the internal electric field between the g-C 3 N 4 and rGO is beneficial in solving the local pH reduction problem and electron transport. Consequentially, our study elucidates that 2D/2D structure, inducing the internal electric field, is an effective way to enhance the performance of the full water-splitting system. [ABSTRACT FROM AUTHOR]

• Boron was incoporated in situ into N-doped carbon by a one-step plasma synthesis. • Boron incorporation has significant boosted the OER performance in N-doped carbon. • DFT indentified boron as a major OER active sites in B,N-codoped carbon. • The OH* chemisorption energy on B,N-codoped carbon is more negatively than N-doped carbon. • The B,N-codoped carbon catalyst outperformed commercial Ru/C in OER performance. The exploration of high-efficiency electrocatalysts for water splitting is significant for large-scale hydrogen production. Herein, boron atoms were incorporated into nitrogen-doped carbon as electrocatalyst through a one-step plasma synthesis route. The obtained B,N-codoped catalyst presented superior electrocatalytic performance, with an onset potential of 1.46 V vs RHE and corresponding overpotentials of 270 mV and 509 mV at current densities of 10 and 100 mA cm−2, which were significantly lower than that of N-doped carbon (1.56 V vs RHE, 331 mV and 554 mV), and even outperformed the commercial 5 wt% Ru/C (1.48 V vs RHE, 275 mV and 547 mV). Moreover, it exhibited higher stability than Ru/C in 9-h durability test and remained relatively high OER catalytic activities. Density functional theory has verified the OH molecule was firstly adsorbed on the top side of B atom in the B,N-codoped carbon. The OH* chemisorption energy on B,N-codoped carbon was less than that on N-doped carbon catalyst system by 0.281 eV, which translated into a higher kinetic OER activity of B,N-codoped carbon. Combined with the electrochemical performance, boron as OER active sites in B,N-codoped carbon should be considered as a valid strategy to boost the performance of heteroatom-doped carbon OER electrocatalysts. [ABSTRACT FROM AUTHOR]