To explore the surface state of electrocatalysts , herein we developed a surface laser modification (pulsed laser ablation , PLA) approach for the fabrication of NiCo 2 O 4-δ with substantial inner oxygen vacancies (Vo ·· ) and higher exterior Ni 3+ /Ni 2+ ratio. The separated NiCo 2 O 4 nanoplates were transformed to cross-linked NiCo 2 O 4-δ nanostructure through PLA strategy. As compare with the primordial NiCo 2 O 4 produce, the laser-modificated NiCo 2 O 4-δ exhibits higher capacitance, lower overpotential and better electrocatalytic performance. The first-principles calculation proves that the additional energy level is introduced between the valence band and conduction band of L-NiCo 2 O 4-δ . The additional energy level not only benefits the hopping of electrons, but also inhibits the recombination of electron-hole pairs. The X-ray photoelectron spectrum (XPS) confirms that the active sites of the electrocatalytic reaction are Vo ·· , suggesting that the electron structure of catalyst could be adjusted by PLA. The high electrocatalytic activity of laser-modificated NiCo 2 O 4-δ could be ascribed to the synergistic effect of increased number of inner Vo ·· , higher electrochemically active surface area , and dominated Ni oct . Our findings might inspire new thoughts on the tuning the surface state and electronic structure of electrocatalyst.
NiO x plays a vital role in fabricating efficient and stable inverted perovskite solar cells (PSCs). However, the relatively low conductivity and inefficient hole extraction of NiO x hole transport layer (HTL) due to the low Ni 3+ /Ni 2+ ratio limit its use in high-efficiency PSCs. Here, we report a facile strategy to remarkably enhance the electrical conductivity and hole extraction capability of NiO x HTL by simply introducing the small molecule 4- tert -butylpyridine ( t BP) as additive in the NiO x precursor solution. It is revealed that the t BP efficient improves the charge selectivity of the NiO x interface, inducing the preferable p-type carrier concentration on the surface. Consequently, more oxygen is involved in the process of Ni 2+ to Ni 3+ conversion, and the resulting t BP: NiO x HTL exhibits significantly enhanced hole extraction and transport property. In addition, a thin layer of LiF is applied to passivate the surface of NiO x , which enables improved hole migration ability by the dipole effect of LiF and reduced trap state density of the surface. The inverted PSCs (0.16 cm 2 ) fabricated with t BP: NiO x HTL delivers an enhanced efficiency of 20.2% relative to the control devices (17.5%). t BP: NiO x devices with a large area of 1 cm 2 are also demonstrated, which achieve a decent efficiency of 16% with excellent long-term stability.
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