Phosphorus vacancies enriched Ni2P nanosheets as efficient electrocatalyst for high-performance Li–O2 batteries

Reusable Te-Doped Sn-P-I Catalysts With Anti-Healing P Vacancies and Stable I Sites for Efficient Black Phosphorus Growth

Black phosphorus (BP) holds significant potential for various applications, but its widespread use requires the development of efficient and cost-effective preparation methods. Sn-P-I clathrates are identified as potential catalysts for BP growth; however, the intact Sn-P-I structure leads to prolonged preparation times, rapid deactivation, and an unclear catalytic mechanism. In this study, a Te-doping strategy is proposed to simultaneously improve the activity and stability of Sn-P-I catalysts. Te doping induces the formation of Sn─Te bonds, creates intrinsic anti-healing phosphorus vacancies, while also mitigates iodine loss due to the lower electronegativity of Te compared to P. This doping changes the deactivation mechanism of the Sn-I-P from phosphorus saturation to iodine loss in the Te-doped Sn-I-P. To further improve catalyst reusability, an iodination treatment is introduced to reactivate the Te-Sn-P-I catalysts. The optimized Te-Sn-P-I catalyst reduced the reaction time for BP synthesis from 15 h to just 45 min, achieving a BP yield of 96.7%. The reactivation process restores 100% of the catalytic performance.

Electrocatalytic Hydrogenation and Deuteration of Unsaturated C-N Bonds to Amines with Vacancy-Rich Cu3P Nanowires as Catalysts in Aqueous Solution

Renewable energy driven electrochemically hydrogenation of unsaturated C-N bonds with water as a hydrogen source provides an eco-friendly route for amine production. However, the potential commercial applications of this strategy were limited by the lack of relevant extended research. Here we demonstrate an efficient electrochemical hydrogenation system for the formation of amines from nitriles by a vacancy-rich copper phosphide catalyst. The catalytic system achieves a yield of 99 % and a Faraday efficiency of 99 % for the hydrogenation of benzonitrile. Mechanism study shows that benzonitrile is spontaneously adsorbed on the electrode surface and the electrogenerated active adsorbed hydrogen is the key reactive intermediate for hydrogenation. Theoretical calculation results show that vacancy-induced active sites chemisorb the N atom, thus accelerating C≡N bond activation for hydrogenation. Encouragingly, good yields of amines (≥99 %) are obtained when benzonitrile is replaced by a series of aromatic nitriles, heterocyclic nitriles, aliphatic nitriles, and imines. These results show the general applicability of this method for the synthesis of various amines.

Upgrading of Pyrolysis Bio-Oil by Catalytic Hydrodeoxygenation, a Review Focused on Catalysts, Model Molecules, Deactivation, and Reaction Routes

Biomass can be converted into energy/fuel by different techniques, such as pyrolysis, gasification, and others. In the case of pyrolysis, biomass can be converted into a crude bio-oil around 50-75% yield. However, the direct use of this crude bio-oil is impractical due to its high content of oxygenated compounds, which provide inferior properties compared to those of fossil-derived bio-oil, such as petroleum. Consequently, bio-oil needs to be upgraded by physical processes (filtration, emulsification, among others) and/or chemical processes (esterification, cracking, hydrodeoxygenation, among others). In contrast, hydrodeoxygenation (HDO) can effectively increase the calorific value and improve the acidity and viscosity of bio-oils through reaction pathways such as cracking, decarbonylation, decarboxylation, hydrocracking, hydrodeoxygenation, and hydrogenation, where catalysts play a crucial role. This article first focuses on the general aspects of biomass, subsequent bio-oil production, its properties, and the various methods of upgrading pyrolytic bio-oil to improve its calorific value, pH, viscosity, degree of deoxygenation (DOD), and other attributes. Secondly, particular emphasis is placed on the process of converting model molecules and bio-oil via HDO using catalysts based on nickel and nickel combined with other active elements. Through these phases, readers can gain a deeper understanding of the HDO process and the reaction mechanisms involved. Finally, the different equipment used to obtain an improved HDO product from bio-oil is discussed, providing valuable insights for the practical application of this reaction in pyrolysis bio-oil production.

Defect engineering associated with cationic vacancies for promoting electrocatalytic water splitting in iron-doped Ni2P nanosheet arrays

Transition metal phosphides are highly efficient catalysts that do not rely on noble metals, which have shown great potential in replacing noble metal catalysts and contributing to the advancement of the electrocatalytic hydrogen production industry. To further enhance the catalytic performance of transition metal phosphides, researchers have discovered that cationic vacancy defects can be utilized to regulate their electronic structure, thereby improving their catalytic properties. In this research, we present the successful synthesis of a bifunctional Ni2P electrocatalyst (VFe-Ni2P) with cationic vacancy defects through electrodeposition and acid etching techniques. The introduction of cationic vacancies after acid etching is confirmed by electron paramagnetic resonance (EPR) spectroscopy. The VFe-Ni2P electrocatalyst demonstrates excellent catalytic performance in alkaline environments, achieving a current density of 10 mA∙cm-2 at an overpotential of 52 mV for the hydrogen evolution reaction (HER), and the same current density with an overpotential of 154 mV for the oxygen evolution reaction (OER). Additionally, the VFe-Ni2P/NF electrode exhibits remarkable stability over 1000 cyclic voltammetric cycles for both HER and OER. This study presents a novel approach for the synthesis and performance control of highly-efficient transition metal phosphide electrocatalysts, which holds significant importance in the development and design of new energy materials.

Fabrication of CoSe2/CoP with rich selenium- and phosphorus-vacancies and heterogeneous interfaces for asymmetric supercapacitors

CoSe2/CoP with rich Se- and P-vacancies and heterogeneous interfaces (v-CoSe2/CoP) is grown on the surface of nickel foam via a two-step strategy: electrodeposition and NaBH4 reduction, which can be used as the cathode material in asymmetric supercapacitors. The SEM characterization reveals the honeycomb-like structure of the v-CoSe2/CoP, and the results of EPR, XPS and HRTEM reveal the existence of anionic vacancies and heterogeneous interfaces in the v-CoSe2/CoP. The as-fabricated v-CoSe2/CoP exhibits high specific capacitance (3206 mF cm-2 at 1.0 mA cm-2) and cyclic stability (91 % capacitance retention after 2000 cycles). An asymmetric supercapacitor is assembled by using the v-CoSe2/CoP and activated carbon (AC) as cathode and anode materials, respectively, which displays a high energy density of 40.6 Wh kg-1 at the power density of 211.5 W kg-1. The outstanding electrochemical performances of the v-CoSe2/CoP might be ascribed to the synergistic effects of Se- and P-vacancies and the heterogeneous interfaces in the v-CoSe2/CoP.

Nickel Phosphonate MOF Derived N-Doped Carbon-Coated Phosphorus-Vacancies-Rich Ni2 P Particles as Efficient Bifunctional Oxygen Electrocatalyst

The design of non-noble metal bifunctional electrocatalysts with outstanding performance and remarkable stability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most essential issues to the realization of rechargeable zinc-air battery, and transition metal phosphides (TMPs) have emerged as robust candidates for oxygen electrocatalysts. Herein, N-doped carbon-coated phosphorus-vacancies-rich Ni2 P particles (Vp -Ni2 P@NC) is proposed via simple carbonization and following Ar plasma treatment from a single nickel phosphonate metal-organic framework (MOF) without extra phosphine and nitrogen sources. The facile and rapid plasma treatment can achieve phosphorus vacancies which could modulate the electronic structure to enhance the inherent active and electrical conductivity. Meanwhile, the pyridine-N and graphitized-N produced during calcination also could provide more active sites and increase the electrical conductivity. The resultant Vp -Ni2 P@NC catalyst shows excellent bifunctional electrocatalytic activity (OER/ORR) based on synergistic effect of introducing P vacancies into Ni2 P and N-doped carbon. Vp -Ni2 P@NC catalyst shows more advantageous ΔE value (0.70 V) compared to Pt/C+RuO2 (0.73 V) and most reported catalysts. Additionally, the zinc-air bbatterie (ZAB) employing Vp -Ni2 P@NC as air cathode shows excellent performance. The maximum power density of 203.48 mW cm-2 , the cycling stability of more than 150 h at 10 mA cm-2 .

Electrochemical sensor for sensitive detection of bisphenol A based on molecularly imprinted TiO2 with oxygen vacancy

Bisphenol A (BPA) is an endocrine disrupting chemical and broadly used in plastics. The leakage of BPA in food and water cycles poses a significant risk to the environment and human health. Thus, monitoring the concentration of BPA to avoid its potential risk is highly important. In this work, a simple and efficient oxygen deficient molecularly imprinted TiO2 electrochemical sensor was proposed for the detection of BPA. The introduction both oxygen vacancies and molecular imprinting evidently enhanced the electrochemical oxidation signal of BPA. The sensor had a good linear response ranging from 0.01 μM to 20 μM with a limit of detection of 3.6 nM. Additionally, the sensor showed remarkable stability, reproducibility and interference resistant ability. It also exhibits excellent recovery during the detection of real water. These findings suggested that the sensor has the potential to be developed as a simple, efficient and low-cost monitoring system for the monitoring of BPA in water.

Electron transfer and surface activity of NiCoP-wrapped MXene: cathodic catalysts for the oxygen reduction reaction

NiCoP constructed on a conductive substrate can achieve efficient oxygen reduction reaction (ORR) catalytic activity. Herein, we report the in-situ growth of NiCoP on the surface of an MXene nanosheet (MXene@NiCoP). The MXene nanosheet accelerated the electron transfer and enhanced the surface activity of the NiCoP. Density functional theory calculations indicated that MXene@NiCoP possessed the advantages of a low overpotential and high OH* adsorption energy in the ORR process. MXene@NiCoP proved to be a highly active catalyst for the ORR with a half-wave potential of 0.71 V vs. RHE. The assembled single-chamber air-cathode microbial fuel cell obtained high electricity generation performance.

Phosphorus vacancy-engineered Ce-doped CoP nanosheets for the electrocatalytic oxidation of 5-hydroxymethylfurfural

The electrooxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furanedioic acid (FDCA) has received increasing attention. To achieve satisfactory electrooxidation of HMF, the development of an efficient electrocatalyst is particularly critical. Herein, porous Ce-CoP nanosheets integrating Ce doping and P vacancies are designed through a deep eutectic solvent approach, and they allow the excellent electrocatalytic oxidation of HMF to FDCA in 1 M KOH electrolyte with 100% HMF conversion, 98% FDCA yield, and a faradaic efficiency of 96.4% at low potential.

Hexamethylenetetramine induced multidimensional defects in Co2P nanosheets for efficient alkaline hydrogen evolution

Crystal engineering is an important way to improve the catalytic performance of transition-metal phosphides. In this work, we propose a strategy for constructing multi-dimensional defects induced by hexamethylenetetramine, which effectively introduces grain boundaries, N doping and P vacancies into Co₂P nanosheets, and improves the activity and stability of the catalyst. Due to the synergistic effect of the multi-dimensional defects, the Co₂P nanosheets exhibit excellent HER catalytic performance, especially at a large current density of 100 mA cm^-2 with an overpotential of only 159 mV. Under 1 M KOH electrolyte and current density of 10 mA cm^-2, the long-term test for 36 h shows that the catalyst maintains a very high stability.

Interfacial Electron Redistribution of Hydrangea-like NiO@Ni2 P Heterogeneous Microspheres with Dual-Phase Synergy for High-Performance Lithium-Oxygen Battery

Lithium-oxygen batteries (LOBs) with ultra-high theoretical energy density (≈3500 Wh kg^-1 ) are considered as the most promising energy storage systems. However, the sluggish kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) can induce large voltage hysteresis, inferior roundtrip efficiency and unsatisfactory cyclic stability. Herein, hydrangea-like NiO@Ni₂ P heterogeneous microspheres are elaborately designed as high-efficiency oxygen electrodes for LOBs. Benefitting from the interfacial electron redistribution on NiO@Ni₂ P heterostructure, the electronic structure can be modulated to ameliorate the chemisorption of the intermediates, which is confirmed by density functional theory (DFT) calculations and experimental characterizations. In addition, the interpenetration of the PO bond at the NiO@Ni₂ P heterointerface leads to the internal doping effect, thereby boosting electron transfer to further improve ORR and OER activities. As a result, the NiO@Ni₂ P electrode shows a low overpotential of only 0.69 V, high specific capacity of 18254.1 mA h g^-1 and superior long-term cycling stability of over 1400 h. The exploration of novel bifunctional electrocatalyst in this work provides a new solution for the practical application of LOBs.

Constructed Interfacial Oxygen-Bridge Chemical Bonding in Core-Shell Transition Metal Phosphides/Carbon Hybrid Boosting Oxygen Evolution Reaction

A designed structure which CoP nanoparticles (NPs) ingeniously connected with graphene-like carbon layer via in-situ generated interfacial oxygen-bridge chemical bonding was achieved by a mild phosphorization treatment. The results proved that the presence of phosphorus vacancies is a crucial factor enabling formation of Co-O-C bonds. The direct coupling of edge Co of CoP with the oxygen from functional groups on the carbon layer was proposed. As a catalyst for electrocatalytic water splitting, the manufactured Fe₂ O₃ @C@CoP core-shell structure manifested a low overpotential of 230 mV, a low Tafel slope of 55 mV dec^-1 , and long-term stability. Density functional theory calculations verified that the Co-O-C bond played a critical role in decreasing the thermodynamic energy barrier of reaction rate-determining step for the oxygen evolution reaction (OER). This synthetic route might be extended to construct metal-O-C bonds in other transition metal phosphides (or selenides, sulfides)/carbon composites for highly efficient OER catalysts.

Structure-regulated Ru particles decorated P-vacancy-rich CoP as a highly active and durable catalyst for NaBH4 hydrolysis

NaBH₄ is considered the best hydrogen storage material due to its high hydrogen content of 10.6 wt% and good stability. However, NaBH₄ hydrolysis requires an efficient catalyst because of the sluggish reaction kinetics. In this work, we have demonstrated a process of preparing a cobalt phosphide-supported Ru particulate nanocatalyst with abundant phosphorus vacancies for the first time. Electron paramagnetic resonance and transmission electron microscopy revealed that the synthesized Ru_9.8/r-CoP catalyst has ample phosphorus vacancies, and Ru species are small particles (~2.5 nm) with uniform dispersion, respectively. More importantly, the optimized Ru_9.8/r-CoP catalyst has the lowest activation energy (45.3 kJ mol^-1) and exhibits excellent catalytic performance for NaBH₄ hydrolysis with a high hydrogen generation rate 9783.3 mLH₂ min^-1 g_cat^-1 at 25 °C, which is higher than most of the cobalt-based catalysts. Moreover, the Ru_9.8/r-CoP catalyst also shows good reusability. For example, the catalytic performance only declined by ca. 14% after five cycles. The excellent catalytic performance of Ru_9.8/r-CoP is attributed to the abundant phosphorus vacancies along with a large specific surface area of r-CoP, which makes the Ru particles smaller and more uniformly dispersed on the surface, thereby exposing more active sites to show improved performance.

Defect engineering and characterization of active sites for efficient electrocatalysis

Electrocatalysis plays a decisive role in various energy-related applications. Engineering the active sites of electrocatalysts is an important aspect to promote their catalytic performance. In particular, defect engineering provides a feasible and efficient approach to improve the intrinsic activities and increase the number of active sites in electrocatalysts. In this review, recent investigations on defect engineering of a wide range of electrocatalysts such as metal-free carbon materials, transition metal oxides, transition metal dichalcogenides and metal-organic frameworks (MOFs) will be summarized. Different defect creation strategies will be outlined, for example, heteroatom doping and removal, plasma irradiation, hydrogenation, amorphization, phase transition and reduction treatment. In addition, we will overview the commonly used advanced characterization techniques that could confirm the existence and identify the detailed structures, types and concentration of defects in electrocatalysts. The defect characterization tools are beneficial for gaining an in-depth understanding of defects on electrocatalysis and thus could reveal the structure-performance relationship. Finally, the major challenges and future development directions on defect engineering of electrocatalysts will be discussed.