friendly approach as a zero-carbon emission process. Recently, transition metal phosphides, carbides, nitrides, and chalcogenides have been extensively studied as cost-effective candidates to replace precious-metal-based materials, such as Pt, Pd, Ir, Ru, and their alloys, which are the most efficient catalysts for the hydrogen evolution reaction (HER). [1][2][3][4][5] Non-noble metal-based phosphides such as nickel phosphide (Ni 2 P) have been exploited as an excellent HER catalyst due to their outstanding activity related to the exposed (001) surface. [6,7] Although the use of nickel phosphides as efficient nonprecious electrocatalysts has rapidly become a hot topic, the electrocatalytic activity of Ni 2 P is still far from satisfactory for replacing precious-metal-based catalysts due to their intrinsically poor conductivity and durability, particularly in acidic electrolysis. [6,8] A promising approach for overcoming these limitations is to couple Ni 2 P with highly conductive substrates such as carbon nanotubes (CNTs), carbon cloth/ paper, and graphene for faster electron transport. [9][10][11] Despite all these efforts, the full catalytic activity of Ni 2 P-based electrocatalysts is yet unrealized in comparison with that of noble metals. Hence, a hybridization between Ni 2 P nanospheres (NSs) and a high conductive Mxene substrate Interface modulation of nickel phosphide (Ni 2 P) to produce an optimal catalytic activation barrier has been considered a promising approach to enhance the hydrogen production activity via water splitting. Herein, heteronucleimediated in situ growth of hollow Ni 2 P nanospheres on a surface defectengineered titanium carbide (Ti 3 C 2 T x ) MXene showing high electrochemical activity for the hydrogen evolution reaction (HER) is demonstrated. The heteronucleation drives intrinsic strain in hexagonal Ni 2 P with an observable distortion at the Ni 2 P@Ti 3 C 2 T x MXene heterointerface, which leads to charge redistribution and improved charge transfer at the interface between the two components. The strain at the Ni 2 P@Ti 3 C 2 T x MXene heterointerface significantly boosts the electrochemical catalytic activities and stability toward HER in an acidic medium via a combination between experimental results and theoretical calculations. In a 0.5 m H 2 SO 4 electrolyte, the Ni 2 P@Ti 3 C 2 T x MXene hybrid shows excellent HER catalytic performance, requiring an overpotential of 123.6 mV to achieve 10 mA cm −2 with a Tafel slope of 39 mV dec −1 and impressive durability over 24 h operation. This approach presents a significant potential to rationally design advanced catalysts coupled with 2D materials and transition metal-based compounds for state-of-the-art high efficiency energy conversions.

In this study, a solution-processable compact vanadium oxide (V2O5) film with a globular nanoparticulate structure is introduced to the hole transport layer (HTL) of polymer bulk-heterojunction based solar cells comprised of PTB7:PC70BM by using a facile metal-organic decomposition method to replace the conventionally utilized poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). For this, a biocompatible structure-determining agent, polyethylene glycol (PEG, Mn 300), is used as an additive in the precursor to form the nanoparticulate compact V2O5 (hereafter referred to as NP-V2O5) film, which possesses an outstandingly smooth surface morphology. The introduction of NP-V2O5 HTL via the solution process with a neutral pH condition successfully improved the stability by preventing the decomposition of indium tin oxide (ITO) glass and the penetration of heavy-metal components and moisture, which are considered as the crucial drawbacks of using PEDOT:PSS. Over 1440 h (60 days) of the stability test, an organic solar cell (OSC) with NP-V2O5 showed a significant durability, maintaining 82% of its initial power conversion efficiency (PCE), whereas an OSC with PEDOT:PSS maintained 51% of its initial PCE. Furthermore, due to the positive effects of the modified surface properties of NP-V2O5, the PCE was slightly enhanced from 7.47% to 7.89% with a significant improvement in the short-circuit current density and fill factor.

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