Theoretical Investigation of HER and OER Electrocatalysts Based on the 2D R-graphyne Completely Composed of Anti-Aromatic Carbon Rings

Based on the DFT calculations, two-dimensional (2D) R-graphyne has been demonstrated to have high stability and good conductivity, which can be conducive to the relevant electrocatalytic activity of the material. Different from the poor graphene, R-graphyne, which is completely composed of anti-aromatic structural units, can exhibit certain HER catalytic activity. In addition, doping the TM atoms in Group VIIIB can be considered an effective strategy to enhance the HER catalytic activity of R-graphyne. Particularly, Fe@R-graphyne, Os@R-graphyne, Rh@R-graphyne and Ir@R-graphyne can exhibit higher HER catalytic activities due to the formation of more active sites. Usually, the shorter the distance between the TM and C atoms is, the better the HER activity of the C-site is. Furthermore, doping Ni and Rh atoms of Group VIIIB can significantly improve the OER catalytic performance of R-graphyne. It can be found that ΔG_O* can be used as a good descriptor for the OER activities of TM@R-graphyne systems. Both Rh@R-graphyne and Ni@R-graphyne systems can exhibit bifunctional electrocatalytic activities for HER/OER. In addition, all the relevant catalytic mechanisms are analyzed in detail. This work not only provides nonprecious and highly efficient HER/OER electrocatalysts, but also provides new ideas for the design of carbon-based electrocatalysts.

Doping P atom with a lone pair: an effective strategy to realize high HER catalytic activity and avoid deactivation under wide H* coverage on 2D silicene and germanene by increasing the structural rigidity

In view of the weak aromatic characteristic resulting from the weak π-bonding ability (different from the analogous graphene), employing two-dimensional (2D) silicene and germanene monolayers could be one of the most promising ways to realize a new type of highly efficient and nonprecious catalyst for the hydrogen evolution reaction (HER). However, the HER activity of pristine silicene and germanene has to be improved, although both of them can exhibit a good change trend. Particularly, the hydrogen phenomenon can occur under moderate or high H* coverage on 2D silicene and germanene. To overcome these bottlenecks, in this study we identify the most effective strategy through doping P with a lone pair to significantly improve the HER catalytic activity under a high H* coverage, by screening a series of IIIA (i.e., B, Al, Ga, In and Tl) and VA (i.e., N, P, As, Sb and Bi) heteroatoms with different electronegativity under detailed DFT calculations. It is revealed that the doped P atoms and almost all the Si/Ge atoms can uniformly serve as highly active sites. Especially, in view of the existence of the lone pair, doping P effectively prevents hydrogenation (even under full H* coverage) by increasing the structural rigidity. Moreover, the P-doping concentration also plays a crucial role in obtaining high HER activity. The relevant mechanisms have been analyzed in detail. Clearly, all these fascinating findings are beneficial for realizing new HER electrocatalysts based on the excellent silicene or germanene nanomaterials, and even other Si/Ge-related materials in the near future.

Polyvinylpyrrolidone assisted transformation of Cu-MOF into N/P-co-doped Octahedron carbon encapsulated Cu3P nanoparticles as high performance anode for lithium ion batteries

The large volume expansion and poor electrical conductivity of copper phosphide (Cu₃P) during the cycle limit their further application as anode of lithium-ion batteries. Therefore, polyvinylpyrrolidone (PVP) modified Cu₃(BTC)₂-derived (BTC = 1, 3, 5-Benzentricarboxylic acid) in-situ N/P-co-doped Octahedron carbon encapsulated Cu₃P nanoparticles (Cu₃P@NPC) are successfully prepared through a two-step process of carbonization and phosphating. The N/P-co-doped Octahedron carbon matrix improves the conductivity of Cu₃P and moderates the volume expansion during the lithiation/delithiation process. Meanwhile, the interaction between the Cu₃P and the doped carbon matrix is methodically explored by using density functional theory (DFT). Through the analysis of the partial charge density, the density of states and the Bader charge, and the calculation results verify the correctness of the experimental observation results, that is, Cu₃P@NPC has good electrochemical performance. The results show that Cu₃P@NPC, as the anode of Lithium-ion batteries, has excellent electrochemical performance: it exhibits satisfactory rate performance (251.9 mAh g^-1 at 5.0 A g^-1) and excellent cycle performance (336.4 mAh g^-1 at 1 A g^-1 over 1000 cycles). This article provides an effective strategy for the encapsulation of metal phosphide nanoparticles in a doped carbon matrix.

Achieving low-energy consumption water-to-hydrogen conversion via urea electrolysis over a bifunctional electrode of hierarchical cuprous sulfide@nickel selenide nanoarrays

Replacing sluggish oxygen evolution reaction with thermodynamically favorable urea oxidation reaction is a promising strategy for hydrogen-generation from water with low-energy consumption. However, the involved six-electron transfer process makes it formidable and seems critical. Hence, exploring high-efficient and low-cost bifunctional catalysts toward urea electrolysis is highly desirable. Herein, hierarchical cuprous sulfide@nickel selenide nanowire arrays were grown on copper foam (termed as Cu₂S@Ni₃Se₂) via a developed method composed of in situ chemical deposition, ion exchange and electrodeposition. The as-prepared bifunctional Cu₂S@Ni₃Se₂ not only shows remarkable hydrogen evolution reaction (HER) activity but also affords excellent urea oxidation reaction (UOR) activity. A subsequently configured Cu₂S@Ni₃Se₂//Cu₂S@Ni₃Se₂ full-cell (Cu₂S@Ni₃Se₂ working as both anode and cathode) only requires a low voltage of 1.48 V to launch a current density of 10 mA cm^-2, not only surpassing the routine water electrolysis (1.70 V), but also outperforming the state-of-the-art Pt/C//IrO₂ for urea electrolysis (1.65 V). Moreover, the performance is superior to most recently reported ones that configured with other catalysts. This work presents a solid step for hydrogen-generation from water with low-energy consumption.

Heteroatom-Doping of Non-Noble Metal-Based Catalysts for Electrocatalytic Hydrogen Evolution: An Electronic Structure Tuning Strategy

Electrocatalytic water splitting for hydrogen production is an appealing way to reduce carbon emissions and generate renewable fuels. This promising process, however, is limited by its sluggish reaction kinetics and high-cost catalysts. Construction of low-cost and high-performance non-noble metal-based catalysts have been one of the most effective approaches to address these grand challenges. Notably, the electronic structure tuning strategy, which could subtly tailor the electronic states, band structures, and adsorption ability of the catalysts, has become a pivotal way to further enhance the electrochemical water splitting reactions based on non-noble metal-based catalysts. Particularly, heteroatom-doping plays an effective role in regulating the electronic structure and optimizing the intrinsic activity of the catalysts. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the hetero-dopants in catalysts yet remains ambiguous. Herein, the recent progress is comprehensively reviewed in heteroatom doped non-noble metal-based electrocatalysts for hydrogen evolution reaction, particularly focus on the electronic tuning effect of hetero-dopants in the catalysts and the corresponding synthetic pathway, catalytic performance, and activity origin. This review also attempts to establish an intrinsic correlation between the localized electronic structures and the catalytic properties, so as to provide a good reference for developing advanced low-cost catalysts.

Electrospinning metal Phosphide/Carbon nanofibers from Phytic Acid for hydrogen evolution reaction catalysts

This paper reports a general electrospinning method to prepare various metal phosphide/carbon nanofibers composite for electrochemical hydrogen evolution reaction (HER) catalysts. An earth-abundant organic acid-phytic acid is successfully incorporated into a conventional electrospinning precursor as the phosphorus source, and continuous nanofibers can be obtained through spinning. After heat treatment, metal phosphide/carbon composite nanofibers can be obtained, with fine phosphide nanoparticles well dispersed on the surface of an interconnected carbon backbone network. Such fibrous structures offer fast charge transfer pathways and enlarged active surface area, which are beneficial for electrocatalysts. As a result, enhance HER catalytic activity can be achieved.

Embedding tetrahedral 3d transition metal TM4 clusters into the cavity of two-dimensional graphdiyne to construct highly efficient and nonprecious electrocatalysts for hydrogen evolution reaction

Coupled with the high structural stability and good conductivity, all the new 2D composite nanostructures TM₄@GDY (TM = Sc, Ti, Mn, Fe, Co, Ni and Cu) can uniformly exhibit considerably high catalytic activity for hydrogen evolution reaction.

Vertically aligned MoS2 nanosheets on N-doped carbon nanotubes with NiFe alloy for overall water splitting

Schematic illustration of the formation process and performance of overall water splitting for NiFe-NCNT@MoS₂ samples.

Theoretical predication of the high hydrogen evolution catalytic activity for the cubic and tetragonal SnP systems

Both the cubic and tetragonal SnP systems, with a layered structure similar to phosphorene, can exhibit a considerably high HER catalytic activity over a wide range of hydrogen coverage.

Theoretical design of a series of 2D TM–C3N4 and TM–C3N4@graphene (TM = V, Nb and Ta) nanostructures with highly efficient catalytic activity for the hydrogen evolution reaction

Coupled with high structural stability and metallic conductivity, all of the new composite systems TM–C₃N₄ and TM–C₃N₄@graphene (TM = V, Nb and Ta) can possess considerably high catalytic activity for the hydrogen evolution reaction.

Earth-Abundant Transition-Metal-Based Electrocatalysts for Water Electrolysis to Produce Renewable Hydrogen

Fundamentals of water electrolysis, and recent research progress and trends in the development of earth-abundant first-row transition-metal (Mn, Fe, Co, Ni, Cu)-based oxygen evolution reaction (OER) and hydrogen evolution (HER) electrocatalysts working in acidic, alkaline, or neutral conditions are reviewed. The HER catalysts include mainly metal chalcogenides, metal phosphides, metal nitrides, and metal carbides. As for the OER catalysts, the basic principles of the OER catalysts in alkaline, acidic, and neutral media are introduced, followed by the review and discussion of the Ni, Co, Fe, Mn, and perovskite-type OER catalysts developed so far. The different design principles of the OER catalysts in photoelectrocatalysis and photocatalysis systems are also presented. Finally, the future research directions of electrocatalysts for water splitting, and coupling of photovoltaic (PV) panel with a water electrolyzer, so called PV-E, are given as perspectives.

Highly efficient catalytic activity for the hydrogen evolution reaction on pristine and monovacancy defected WP systems: a first-principles investigation

A deep understanding of HER catalytic activity of tungsten phosphide at the atomic level and its effective improvement by introducing a monovacancy.