Phosphide Catalysts Research Articles

Br‐Induced d‐Band Regulation on Superhydrophilic Isostructural Cobalt Phosphide for Efficient Overall Water Splitting

AbstractHighly efficient novel electrocatalysts for hydrogen/oxygen production are urgently required, for noble metal‐based catalysts substitution. Cobalt phosphides have shown great potential for serving as bifunctional catalysts, owing to the cost effectiveness and high conductivity. However, the water splitting ability of them is still not comparative with commercial noble counterparts. In this work, we reported a Br‐induced strategy, to obtain an ultra‐hydrophilic isostructural Br0.036─Co1.085P@NF catalyst by a gas‐solid reaction method. As a typical halogen element, the introduction of Br can greatly enhance the surficial hydrophilicity and thus further impart ideal adsorption ability for water molecules. Meanwhile, the electronic structure could be regulated to further induce the generation of isostructural cobalt phosphides (CoP/Co2P). As a result, the contact angle of Br0.036─Co1.085P@NF catalysts nearly cannot be caught owing to the ultra‐hydrophilicity. It is also confirmed that, the d‐band center of Co shows apparent negative shift after Br introduction, which reduces the adsorption energy of oxygen‐containing intermediates thereby facilitating the desorption process. Besides, the introduction of Br can also reduce the barrier of O2 formation, show more favorable dynamic behaviors. This work proved the accessibility for an effective design strategy on halogen‐induced isostructural transition metal phosphides catalysts for high‐performance overall water splitting.

Regulating the electronic structure of nickel phosphides via interface engineering and molybdenum doping boosts benzyl alcohol oxidation coupled with hydrogen production

Coupling the electrocatalytic benzyl alcohol oxidation reaction (BAOR) with hydrogen evolution reaction (HER) presents a favorable energy conversion method. However, the development of highly efficient bifunctional electrocatalysts poses significant challenges. In this study, a Mo doped biphasic Ni2P-Ni12P5 heterostructure (Mo-Ni2P/Ni12P5@NF) has been developed to serve as the efficient bifunctional electrocatalyst. The Mo-Ni2P/Ni12P5@NF resulted in exceptional activities for both the BAOR and HER. The electrolyzer cell using Mo-Ni2P/Ni12P5@NF as anode and cathode operates at an impressively low cell voltage of merely 1.38 V to achieve the current density of 10 mA cm−2 in a benzyl alcohol-containing aqueous solution. Experimental results and density functional theory (DFT) calculations indicate that the introduction of Mo can significantly modulate the electronic structure of Ni-based phosphide catalysts and adjust for the d-band center of the active Ni sites. This modulation significantly optimizes the adsorption capabilities for both benzyl alkoxide (Ph-CH2O-) and the H* intermediates on Mo-Ni2P/Ni12P5@NF, thereby increasing electrocatalytic activity toward BAOR and HER respectively. Our work offers a valuable insight into designing bifunctional electrocatalysts and highlights the potential of Mo doping systems to produce hydrogen and value-added products efficiently.

Selective Production of Sorbitol from Glucose over Humic Acid-Derived Carbon-Supported Nickel Phosphide Catalysts

Selective Production of Sorbitol from Glucose over Humic Acid-Derived Carbon-Supported Nickel Phosphide Catalysts

A high-performance porous carbon coated CoxP dual functional catalyst for upgrading of furfuryl alcohol

Cobalt phosphides exhibit dual catalytic characteristics as both metal and acid, rendering them widely employed in the organic chemicals refining. Yet, their utilization in the hydrodeoxygenation of furanic molecules derived from biomass remains underexplored. In this study, we fabricated a porous carbon coated cobalt phosphide catalysts (CoxP@C) by pyrolysis and gas-phosphidation of Co-MOFs, and systemically elucidated the synergistic effect of Co-P on hydrodeoxygenation of furfuryl alcohol to produce 2-methyl furan. Phosphidation generated a substantial quantity of positively-charged Coδ+ species through Co-P bonding, and the intensified charge-transfer from cobalt to phosphorous caused the Coδ+ species more electro-deficiency, and enhanced both hydrogen dissociation centers and acid sites when the P/Co molar ratio reached 1.2, thereby synergically boosting hydrodeoxygenation performance. The optimized CoxP@C achieved a 90 % yield of 2-methyl furan under mild conditions (140 °C and 2.5 MPa), while also demonstrating robust recyclability. This study underscores the potential benefits of cobalt phosphide catalyst for the hydrogenative upgrading of biomass-derived molecules.

Improved Nitrate-to-Ammonia Electrocatalysis through Hydrogen Poisoning Effects.

Electrochemical conversion from nitrate to ammonia is a key step in sustainable ammonia production. However, it suffers from low productive efficiency or high energy consumption due to a lack of desired electrocatalysts. Here we report nickel cobalt phosphide (NiCoP) catalysts for nitrate-to-ammonia electrocatalysis that display a record-high catalytic current density of -702±7 mA cm-2, ammonia production rate of 5415±26 mmol gcat-1 h-1 and Faraday efficiency of 99.7±0.2 % at -0.3 V vs. RHE, affording the estimated energy consumption as low as 22.7 kWh kgammonia-1. Theoretical and experimental results reveal that these catalysts benefit from hydrogen poisoning effects under low overpotentials, which leave behind catalytically inert adsorbed hydrogen species (HI*) at Co-hollow sites and thereupon enable ideally reactive HII* at secondary Co-P sites. The dimerization between HI* and HII* for H2 evolution is blocked due to the catalytic inertia of HI* thereby the HII* drives nitrate hydrogenation timely. With these catalysts, the continuous ammonia production is further shown in an electrolyser with a real energy consumption of 18.9 kWh kgammonia-1.

Bimetallic MoFe phosphide catalysts for the hydrogen evolution reaction

In this work, highly efficient and stable (bi)metallic phosphides were prepared by a facile, flexible, and controllable sol-gel method followed by sintering. This novel approach allowed to avoid complicated and dangerous phosporization using, e.g. red phosphorus. The doping of the MoP catalysts with Fe was used to further boost their catalytic performance. Monometallic MoP and Mo3P, as well as bimetallic MoFeP were tested in both acidic and alkaline environments and showed remarkable results. The incorporation of Fe enabled the creation of a scalable and cost-effective catalyst for the hydrogen evolution reaction due to the synergy between Fe and Mo in the bimetallic phosphides. Using MoFeP for catalysing the hydrogen evolution reaction, overpotentials of only -132 mV (in an acidic medium) and -142 mV (in an alkaline medium) were needed to reach current density of -10 mA.cm−2, indicating the possibility of use this catalyst in a large pH range. Its high catalytic activity was maintained even at current density of -100 mA.cm−2 as documented by overpotentials of -202 mV and -246 mV in acid and alkaline environment, respectively. This, along with excellent stability and durability confirms its promising potential for incorporation into industrially relevant applications. The experimental data were confirmed by computational (DFT) results, showcasing that incorporation of Fe caused an increase in the number of active sites with Gibbs adsorption energy close to zero.

Regulating Reconstruction-Engineered Active Sites for Accelerated Electrocatalytic Conversion of Urea.

Reconstruction-engineered electrocatalysts with enriched high active Ni species for urea oxidation reaction (UOR) have recently become promising candidates for energy conversion. However, to inhibit the over-oxidation of urea brought by the high valence state of Ni, tremendous efforts are devoted to obtaining low-value products of nitrogen gas to avoid toxic nitrite formation, undesirably causing inefficient utilization of the nitrogen cycle. Herein, we proposed a mediation engineering strategy to significantly boost high-value nitrite formation to help close a loop for the employment of a nitrogen economy. Specifically, platinum-loaded nickel phosphides (Pt-Ni2P) catalysts exhibit a promising nitrite production rate (0.82 mol kWh-1 cm-2), high stability over 66 h of Zn-urea-air battery operation, and 135 h of co-production of nitrite and hydrogen under 200 mA cm-2 in a zero-gap membrane electrode assembly (MEA) system. The in situ spectroscopic characterizations and computational calculations demonstrated that the urea oxidation kinetics is facilitated by enriched dynamic Ni3+ active sites, thus augmenting the "cyanate" UOR pathway. The C-N cleavage was further verified as the rate-determining step for nitrite generation.

CoNi-phosphides with iron incorporation effectively boost hydrogen evolution reaction and oxygen evolution reaction for overall water splitting

Rational design of high-efficiency, durable and cost-effective electrocatalysts for H2 production is essential to accelerate hydrogen production from fundamental experiments to practical industrial applications. Herein, cobalt-nickel-iron phosphides are constructed on Ni foam (CoNiFeP@NF) via a simple one-step electrochemical deposition method as self-supported electrodes for efficiently water splitting. The introduction of Fe element significantly enhances the catalytic properties of CoNiP@NF electrode for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Additionally, the optimal HER and OER electrodes are obtained by adjusting the Fe3+ concentration at 0.1 (CoNiFeP@NF-0.1) and 0.15 M (CoNiFeP@NF-0.15), respectively. Benefiting from the modulation of the electronic structure of CoNiP by the Fe element, CoNiFeP@NF-0.1 and CoNiFeP@NF-0.15 electrodes only require the overpotentials (η) of 48 mV for HER and 223 mV for OER to reach the current density of 10 mA cm−2, superior to the reference CoNiP@NF electrode (η10, HER = 89 mV, η10, OER = 333 mV). Subsequently, the electrolyzer constructed by CoNiFeP@NF-0.1 as cathode and CoNiFeP@NF-0.15 as anode exhibits excellent overall water splitting performance with a cell voltage of 1.56 V at a current density of 10 mA cm−2. This work provides a convenient and effective strategy for regulating the catalytic activity of bifunctional phosphide catalysts for water splitting.

Electrochemical Nitrogen Fixation at Phosphide Catalyst in Alkaline Medium: Electrocatalytic Approach Toward Validation and Determination of Ammonium Product

A catalytic system based on iron phosphide (Fe2P) has exhibited electrocatalytic activity toward N2-reduction reaction in alkaline medium (0.5 mol dm-3 NaOH). Based on voltammetric stripping-type electroanalytical measurements, Raman spectroscopic and spectrophotometric data, it can be stated that the Fe2P catalyst facilitates conversion of N2 to NH3, and the process is fairly selective with respect to the competing hydrogen evolution. A series of diagnostic electrocatalytic experiments (utilizing platinum nanoparticles and HKUST-1) have been proposed and performed to control purity of nitrogen gas and to probe presence of potential contaminants such as ammonia, nitrogen oxo-species and oxygen. On the whole, the results are consistent with the view that the interfacial reduced-iron (Fe0) centers, while existing within the network of P sites, induce activation and reduction of nitrogen, parallel to the water splitting (reduction) to hydrogen. It is apparent from Tafel plots and impedance measurements that mechanism and dynamics of nitrogen reduction depends on the applied electroreduction potential. The catalytic system exhibits certain tolerance with respect to the competitive hydrogen evolution and gives (during electrolysis at -0.4 V vs. RHE) the Faradaic efficiency, namely, the selectivity (molar) efficiency, toward production of NH3 on the level of 60%. Under such conditions, the NH3-yield rate has been found to be equal to 7.5 µmol cm-2 h-1 (21 µmol m-2 s-1). By referring to classic concepts of electrochemical kinetic analysis, the rate constant in heterogeneous units has been found to be on the moderate level of 1-2*10-4 cm s−1 (at -0.4 V). The above mentioned iron-phosphorous active sites, which are generated on surfaces of Fe2P particles, have also been demonstrated to exhibit strong catalytic properties during reductions of other electrochemically inert reactants, such as oxygen, nitrites and nitrates. Supplementary diagnostic experiments have also been carried out to control purity of nitrogen gas and to identify potential contaminants. To comment on general catalytic activity of Fe2P during electroreductions in alkaline medium, we have performed additional comparative measurements using such redox probes as O2, CO2, NO3 - and NO2 -.

Lanthanum Transition-Metal Sulfide Electrocatalysts for Overall Water Splitting

Hydrogen has been identified as a sustainable energy source for the future with the potential of replacing fossil fuels due to its high gravimetric energy density and zero carbon emissions. Water electrolysis is a promising approach to the clean production of pure hydrogen, however, the benchmark catalysts of the half reactions of water electrolysis are noble-metal based, which limit the application of this technique.1 As well, the high energy barrier and sluggish kinetics of the oxygen evolution reaction limit the efficiency of the system. Therefore, it is crucial to develop robust, stable, and cost-effective materials for water electrolysis to be scalable. Lanthanum transition-metal oxide electrocatalysts have been pursued in the past for water splitting due to the high abundance of lanthanum and transition metals.2 However, these catalysts suffer from low conductivity and inherent instability towards oxygen evolution. Binary sulfides, selenides, and phosphides have also been pursued,3 but the compositional space of these materials is limited. Ternary sulfides offer a wider compositional space that allows fine-tuning for optimal performance. As a result, we have pursued the synthesis and application of the relatively unexplored ternary chalcogenides, LaMS3 (M = Ni, Co, Fe, Mn) towards water electrolysis. The efficiency of water electrolysis and stability of the materials have been tested with linear sweep voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. We found these materials to be active towards both the hydrogen and oxygen evolution reactions, in acidic and alkaline conditions, respectively, with the catalysts exhibiting an activity trend where LaNiS3 > LaCoS3 > LaFeS3 > LaMnS3. For HER, LaNiS3 exhibits an overpotential of 340 mV at 10 mAcm-2 with a Tafel slope of 79 mV/decade. For OER, an overpotential of 373 mV at 10 mAcm-2 and a low Tafel slope of 48 mV/decade are observed. In addition, LaNiS3 proved to be highly stable with minimal change in potential over a period of 18 hours. The high activity and stability of LaNiS3 towards both half reactions of water electrolysis make it a promising candidate for a bifunctional water splitting electrocatalyst.References Wang, S.; Lu, A.; Zhong, C.-J. Hydrogen Production from Water Electrolysis: Role of Catalysts. Nano Convergence 2021, 8 (1), 4.Dias, J. A.; Andrade, M. A. S.; Santos, H. L. S.; Morelli, M. R.; Mascaro, L. H. Lanthanum‐Based Perovskites for Catalytic Oxygen Evolution Reaction. ChemElectroChem 2020, 7 (15), 3173–3192.Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6 (12), 8069–8097.

CoSex and CoSex/Reduced GO Composites as Electrocatalysts for Water Splitting

Hydrogen stands as an attractive energy source, offering a way to meet increasing energy demands without the reliance on fossil fuels and thus harming the environment. Renewable energy sources such as wind, wave and solar power can be used to generate inexpensive electricity, which we can then use to power water electrolysis.1 The generated hydrogen can then be converted back into electricity by using fuel cells, leaving only water as a by-product, rendering this technology clean and devoid of harmful emissions. The electrolysis cell can be operated at normal room temperatures without the need for high pressure rectors. At present, the practical application of hydrogen production using electrochemical water splitting is hindered by electrocatalyst limitations. Currently, the best electrocatalytic materials for water splitting are Platinum-based for the hydrogen evolution reaction (HER) and Ruthenium-based for the oxygen evolution reaction (OER). These materials are expensive and have limited reserves, 2 and therefore cost-effective alternatives must be developed. Transition metal dichalcogenides (TMDs) are of particular interest due to their tuneable structures. 3,4 Herein we have chosen to investigate CoSe2 as a potential electrocatalyst for overall water splitting (OWS). We describe both the electrochemical and solvothermal synthesis of CoSex. The CoSex was then combined with a carbon substrate to create a total of four electrocatalysts. Reduced graphene oxide (rGO) was employed as the carbon substrate and was synthesised via modified Hummer’s method, drop casted on to a GCE and electrochemically reduced to create a rGO modified GCE. The electrodeposited CoSex/rGO composite (ED-CoSex/rGO) was prepared by immersing a rGO modified GCE in an electrodeposition solution and deposited by holding the electrode at a fixed potential for a period of time (Figure 1). The solvothermal/rGO composite ST-CoSex/rGO was prepared by drop casting the solvothermally prepared CoSex ink on top of a rGO modified GCE. While most of the investigation on these electrocatalysts was done using simple glassy carbon electrode (GCE), the best performing material was then screened on a more porous electrode such as Nickel Foam (NF).Materials were characterised using a combination of HR-SEM, XRD, Raman and XPS, while cyclic voltammetry, linear sweep voltammetry and chronoamperometry were employed to examine catalytic activity of the materials. SEM unveiled distinct morphologies, with the electrochemically formed CoSex appearing as flower-like deposits, while sheet-like morphology was seen with the solvothermal synthesis. The solvothermally produced CoSex was more crystalline, as evidenced from XRD. Despite the morphological differences, both CoSex variants exhibited commendable electrochemical attributes.Materials also showed good stability over a period of 18 hours with the ED-CoSex material showing the best performance over 18 hours. Interestingly, all materials showed improved HER performance when subsequently tested after 18 hours via polarisation curves. All materials exhibited high electrochemical active surface areas (ECSA), stability, and favourable low overpotentials for both the hydrogen evolution reaction (HER) and the Oxygen evolution (OER) in alkaline media, however. It is worth noting that while the introduction of rGO significantly lowers the overpotential of electrodeposited and solvothermally synthesised materials, following chronoamperometry, it appears the beneficial effect of the rGO addition is less evident. These results underscore the potential efficacy of CoSex and CoSex composites in facilitating efficient water splitting for hydrogen production, with the potential to rival the performance of platinum-based electrocatalysts. The significance of this research lies in offering sustainable alternatives to platinum in electrolysers, a crucial step toward establishing a more accessible and eco-friendly hydrogen economy.References(1) Jacobson, M. Z.; Delucchi, M. A.; Bazouin, G.; Bauer, Z. A. F.; Heavey, C. C.; Fisher, E.; Morris, S. B.; Piekutowski, D. J. Y.; Vencill, T. A.; Yeskoo, T. W. 100% Clean and Renewable Wind, Water, and Sunlight (WWS) All-Sector Energy Roadmaps for the 50 United States. Energy Environ Sci 2015, 8 (7). https://doi.org/10.1039/c5ee01283j.(2) Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catalysis. 2016. https://doi.org/10.1021/acscatal.6b02479.(3) Minadakis, M. P.; Tagmatarchis, N. Exfoliated Transition Metal Dichalcogenide-Based Electrocatalysts for Oxygen Evolution Reaction. Advanced Sustainable Systems. 2023. https://doi.org/10.1002/adsu.202300193.(4) Sukanya, R.; da Silva Alves, D. C.; Breslin, C. B. Review—Recent Developments in the Applications of 2D Transition Metal Dichalcogenides as Electrocatalysts in the Generation of Hydrogen for Renewable Energy Conversion. J Electrochem Soc 2022, 169 (6). https://doi.org/10.1149/1945-7111/ac7172. Figure 1

Carbon-Monoxide Assisted Synthesis of Cobalt-Nickel Phosphides for Hydrogen Evolution Reaction

Alkaline water electrolysis is a method for production of hydrogen as an alternative source for renewable energy. This method can be completely free of greenhouse gas emissions if it is paired with another alternative energy source, such as solar energy or wind power, to provide the necessary electricity to drive the reaction. Water electrolysis requires catalysts to make that necessary amount of electricity low enough for competitive hydrogen production in the current market. Vast numbers of studies have been performed in an attempt to fill this need for cost-effective catalysts for water electrolysis. This work focuses on the development of synthesis methods for cobalt-nickel phosphide catalysts for the hydrogen evolution reaction (HER) for water electrolysis in alkaline media. The methods for preparation of the catalysts are explored for cobalt, nickel, and cobalt-nickel alloy phosphides in the presence of carbon monoxide as a shape-controlling capping agent. Depending on the condition of carbon monoxide addition, the reaction results in high vs. low-aspect ratio nanorods or nanospheres for mono- or bimetallic cobalt-nickel phosphide nanostructures. These phosphides are then subjected to evaluation for HER via cyclic voltammetry and linear sweep voltammetry to study the effects of morphology on their HER activity. Materials characterization such as XRD, TEM, and ICP-MS are performed before the HER electrochemical evaluation for better understanding of the structure-activity relationship. The catalytic activities of these phosphides are also compared to the noble metal benchmark HER catalyst Pt/C in the same environment at their equal mass loadings. The best-performing phosphide is further tested for HER at increased mass loadings to study the effects of catalyst loadings on the mass transport and thus the activity. Further TEM characterization is performed on the most active catalyst after HER to evaluate morphological stability. It is found that in order to achieve an overpotential at the current density of 100 mA/cm2 comparable to Pt/C for 50 μg/cm2, the necessary loading for the phosphide is 250 µg/cm2.

Development of Fe-Doped Ni2P-POx Electrocatalyst for Oxygen Evolution Reaction

Water electrolysis is extensively researched as a next-generation energy storage method to overcome the intermittency of renewable energy. Electricity generated from renewable sources such as solar and wind power can be converted into pure green hydrogen through water electrolysis. Despite the potential of green hydrogen as a renewable energy storage/carrier medium, the high overpotential resulting from the slow kinetics of oxygen evolution reaction (OER) and the use of expensive noble metals make cost-competitive hydrogen production a significant challenge. Anion exchange membrane water electrolysis (AEMWE) is one method for hydrogen production, offering economic advantages over proton exchange membrane systems as it allows for the use of relatively inexpensive transition metal catalysts like Ni, Fe, and Co due to its alkaline environment.Nickel phosphide (Ni2P)-based catalysts have emerged as highly promising candidates to accelerate the electrocatalytic OER. In particular, the introduction of Fe into Ni2P has been found to induce charge transfer, optimizing the electronic structure and accelerating the OER process. OER catalysts based on transition metal phosphides often exhibit a core-shell structure with phosphide at the core and oxide at the shell during OER measurements. This core-shell structure enhances OER performance through the oxide shell, complementing the deficient electrical conductivity of the phosphide core, resulting in superior catalytic activity and durability. From this perspective, transition metal phosphates are also being studied as electrocatalysts for OER. Phosphates, such as PO3 -, not only promote oxygen adsorbate adsorption but also induce a distorted local metal center geometry that favors OH- adsorption and further oxidation.To address these challenges, this study develops a facile and scalable synthesis of iron-doped nickel phosphide-phosphate (Fe-doped Ni2P-POx) nano-hybrid system as a superior noble-metal free OER powder-catalyst. The utilization of self-filling and pyrolysis approaches facilitates economically viable production of the highly porous phosphide catalyst with a high specific surface area and rough surfaces. X-ray diffractometer, X-ray photoelectron spectroscopy, and electron paramagnetic resonance elucidates the electronic structure modulation, resulting in phosphide-phosphate nano-hybrid structures. Consequently, the catalyst demonstrates excellent OER activity in 1 M KOH, with a significantly low overpotential of 283 mV at 20 mA cm-2, a small Tafel slope of 28.4 mV dec-1, and a superior exchange current density of 8.22 mA cm-2, surpassing state-of-the-art PGM catalysts. Furthermore, its durability over 20 hours indicates its excellent stability, mass transport properties, and mechanical robustness in alkaline media, underscoring its potential as an efficient OER catalyst to facilitate electrocatalytic hydrogen production. Figure 1

Probing Mixed Phase Metallic Ni/Amorphous Nickel Phosphide Nanocatalysts during Oxygen Evolution Reaction Using Operando X-Ray Absorption Spectroscopy

Metal phosphide-containing nanomaterials have demonstrated remarkable efficacy as non-precious metal-based catalysts for the alkaline oxygen evolution reaction (OER). While it is widely acknowledged that various OER catalysts undergo structural reconstruction under applied OER potentials, monitoring these changes is challenging because they are often rapid and require instrumentation not typically found in the typical lab setting. In this study, we utilize operando X-ray absorption spectroscopy (XAS) to determine the structural reconstruction of nickel-based metal phosphide catalysts during OER. We have developed the synthesis of nickel-based phosphide nanoparticles with a range of phosphorus incorporation. These nanoparticles are composed of metallic nickel and amorphous nickel phosphide phases as determined by XRD, TEM and XAS. At low levels of P incorporation, from 2% to 15%, the synthesis results in the mixture of metallic nickel and amorphous phosphide phases. At higher levels of phosphorus incorporation, from 20% to 30%, amorphous nickel phosphide is the predominant phase. Electrochemical characterization of this nickel phosphide series for OER revealed that the catalysts with 20% phosphorus incorporation exhibited superior OER activity. The phosphides with lower phosphorus content, such as 2%, had smaller Ni2+/Ni3+ redox peaks which has been shown to suppress the conversion to Ni(OH)2, leading to lowered OER activity. Increased amorphous nickel phosphide phase led to greater activity, suggesting that the active component in the catalyst comes from the amorphous nickel phosphide phase. Meanwhile, higher phosphorus content (20-30%) where the amorphous phosphide is the predominate phase resulted in larger redox peaks, signifying greater conversion to Ni(OH)2. Operando XAS will be applied to investigate these metallic nickel/nickel phosphide nanocatalysts to elucidate their structural reconstruction during OER

Electron Delocalization Disentangles Activity-Selectivity Trade-Off of Transition Metal Phosphide Catalysts in Oxidative Desulfurization.

Breaking the activity-selectivity trade-off has been a long-standing challenge in catalysis. Here, we proposed a nanoheterostructure engineering strategy to overcome the trade-off in metal phosphide catalysts for the oxidative desulfurization (ODS) of fuels. Experimental and theoretical results demonstrated that electron delocalization was the key driver to simultaneously achieve high activity and high selectivity for the molybdenum phosphide (MoP)/tungsten phosphide (WP) nanoheterostructure catalyst. The electron delocalization not only promoted the catalytic pathway transition from predominant radicals to singlet oxygens in H2O2 activation but also simultaneously optimized the adsorption of reactants and intermediates on Mo and W sites. The presence of such dual-enhanced active sites ideally compensated for the loss of activity due to the nonradical catalytic pathway, consequently disentangling the activity-selectivity trade-off. The resulting catalyst (MoWP2/C) unprecedentedly achieved 100% removal of thiophenic compounds from real diesel at an initial concentration of 2676 ppm of sulfur with a high turnover frequency (TOF) of 105.4 h-1 and a minimal O/S ratio of 4. This work provides fundamental insight into the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire the development of high-performance catalysts for ODS and other catalytic fields.

Regulating Reconstruction‐Engineered Active Sites for Accelerated Electrocatalytic Conversion of Urea

AbstractReconstruction‐engineered electrocatalysts with enriched high active Ni species for urea oxidation reaction (UOR) have recently become promising candidates for energy conversion. However, to inhibit the over‐oxidation of urea brought by the high valence state of Ni, tremendous efforts are devoted to obtaining low‐value products of nitrogen gas to avoid toxic nitrite formation, undesirably causing inefficient utilization of the nitrogen cycle. Herein, we proposed a mediation engineering strategy to significantly boost high‐value nitrite formation to help close a loop for the employment of a nitrogen economy. Specifically, platinum‐loaded nickel phosphides (Pt‐Ni2P) catalysts exhibit a promising nitrite production rate (0.82 mol kWh−1 cm−2), high stability over 66 h of Zn‐urea‐air battery operation, and 135 h of co‐production of nitrite and hydrogen under 200 mA cm−2 in a zero‐gap membrane electrode assembly (MEA) system. The in situ spectroscopic characterizations and computational calculations demonstrated that the urea oxidation kinetics is facilitated by enriched dynamic Ni3+ active sites, thus augmenting the “cyanate” UOR pathway. The C−N cleavage was further verified as the rate‐determining step for nitrite generation.

Robust iron-doped nickel phosphides in membrane-electrode assembly for industrial water electrolysis

Water electrolysis, a pivotal process for the production of green hydrogen, is a crucial step toward realizing the hydrogen economy. To advance its industrialization, it is essential to develop a highly efficient and economical catalyst along with a low-resistance electrolyzers. In pursuit of this goal, we synthesize a cost-effective iron-doped nickel phosphide electrocatalyst through a hydrothermal synthesis followed by post-phosphorization process. This catalyst exhibits exceptional performance, with an overpotential at 10 mA cm-2 (η10) of 216 mV for oxygen evolution reaction, the rate-determining step for water electrolysis. It overperforms the that of pristine nickel phosphide (NiPx, η10 = 284 mV). Operando X-ray absorption spectroscopy reveals the robust nature of the iron-doped nickel phosphide catalyst during water electrolysis, in stark contrast to the pristine nickel phosphide, which undergoes oxidation, thereby impacting overall catalytic activity. When integrated into a membrane-electrode assembly (MEA) system, our iron-doped nickel phosphide displays voltages of 1.51 V at 10 mA cm-2 (EE = 81.5%) and 1.66 V at 100 mA cm-2 (EE = 76.4%) without iR-correction. Moreover, it achieves a current density of 345 mA cm-2 at an applied voltage of 2 V without iR-correction, meeting industrial criteria. These findings underscore the superior catalytic activity of the robust phosphide phase for water electrolysis.

Green diesel synthesis from palm fatty acid distillate using a nickel phosphide catalyst: Optimization by box behnken design

The persistent global energy crisis is propelling significant innovations, including the use of palm fatty acid distillate (PFAD) as a renewable resource for producing green diesel (GD). Therefore, this study aimed to intensify GD synthesis from PFAD by optimizing the process using a Response Surface Methodology-Box Behnken Design (RSM-BBD). Optimization was achieved with a nickel phosphide catalyst supported by natural zeolite through hydrodeoxygenation method. RSM-BBD was used to design the process, considering time (1−3 h), temperature (300–350 °C), catalyst concentration (5–15 %), and pressure (20–60 bar). The results showed that the optimum conditions consisted of 11 % catalyst concentration, 3 h of reaction time, 342 °C temperature, and 29 bar pressure, leading to a 96.35 % GD yield. All conversion parameters, except pressure, significantly influenced GD yield. The quality of the synthesized GD showed high quality and compliance with Indonesian as well as European diesel fuel standards.

Enhanced water‐splitting performance: Interface‐engineered tri‐metal phosphides with carbon dots modification

AbstractDesigning integrated overall water‐splitting catalysts that maintain high efficiency and stability under various conditions is an important trend for future development, yet it remains a significant challenge. Herein, novel nanoflower‐like tri‐metallic Ni–Ru–Mo phosphide catalyst ((Ni–Ru–Mo)P@F‐CDs), integrated with F‐doped carbon dots (F‐CDs), were synthesized via a straightforward hydrothermal process and subsequent phosphatization. Attributable to precise interface engineering and electronic structure optimization, (Ni–Ru–Mo)P@F‐CDs exhibit exceptional bi‐functional catalytic activity in alkaline conditions, achieving remarkably low overpotentials of 231 and 123 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, at a current density of 100 mA cm−2. Industrially, only 1.426 V is needed for the same efficacy. Additionally, the catalyst requires merely 1.508 and 1.564 V for overall water splitting in 1 M KOH and simulated seawater, respectively, at 100 mA cm−2. The catalyst also shows excellent stability, with minimal performance decline over 100 h within 100–200 mA cm−2. Density functional theory calculations indicate that the interface structure synergistically optimizes Gibbs free energy for H* and O* intermediates during HER and OER, respectively, accelerating electrochemical water‐splitting kinetics.

Elucidating the mechanism on carbon nanotube-coated cobalt phosphide catalyst activating PMS to degrade norfloxacin contaminants

Transition metal phosphides have shown great potentials in persulfate activation for eliminating organic contaminants, while the understanding of the activation mechanism still remains fragmentary. Herein, a series of nitrogen-phosphorus-doped carbon nanotube-coated cobalt phosphide catalysts (Co/P-CNTs) were synthesized for activating peroxymonosulfate (PMS) to degrade norfloxacin (NOR). The optimal Co/P-CNTs-0.3 could eliminate NOR up to 97 % within 60 min in the presence of PMS. Results confirm that the synergistic interaction between multi-valent Co species in the Co/P-CNTs significantly contributes to the excellent PMS activation performance. The contribution of reactive oxygen species (ROS) to pollutant removal and the steady-state concentration of free radicals were quantitatively analyzed by means of chemical probe and reaction kinetics. A free radical mechanism dominated by SO4•– and NOR degradation pathway were identified, and the effect of coexisting inorganic anions was systematically evaluated. This study offers profound insights into the activation mechanism of metal phosphides towards environmental remediation.