Introducing High-Valence Iridium Single Atoms into Bimetal Phosphides toward High-Efficiency Oxygen Evolution and Overall Water Splitting

A bi-functional S-scheme cobalt-porphyrin conjugated polymer/C3N4 heterojunction for cooperative CO2 reduction and tetracycline degradation

The design of bifunctional photocatalysts for the removal of contaminants and the reduction of CO2 is of significant practical importance in addressing pollution and energy challenges. However, the photocatalytic efficiency is limited by the inadequate redox ability, high carrier recombination rate, and insufficient reactive sites of existing photocatalysts. Herein, a 2D/2D S-scheme heterojunction composed of cobalt-porphyrin conjugated polymer nanoflakes and C3N4 nanosheets (CoPor-DBE/CN) was rationally synthesized, exhibiting matched redox ability and favorable CO2 adsorption properties. The layered structure and functional groups of CoPor-DBE/CN provide numerous active sites, thereby enhancing the separation and transfer of charge carriers as well as the adsorption of reactants. Under visible light illumination, the optimized 50CoPor-DBE/CN hybrid achieved a CO production rate of 16.7 μmol g-1 h-1 and a tetracycline removal rate of 93.8%, which are significantly higher than those of the individual CN material. By employing X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and photo-irradiated Kelvin probe force microscopy (KPFM), we demonstrate that the transfer of charge carriers within the CoPor-DBE/CN system follows the S-scheme heterojunction mechanism. This work offers a promising blueprint for the design of multifunctional S-scheme photocatalysts aimed at the simultaneous efficient reduction of CO2 and degradation of organic pollutants.

Atomically Dispersed Mn-Ir Sites on 2D Amorphous Carbon Materials Synergistically Boost Electrochemical Overall Water Splitting

Enhancing the activity and durability of noble-metal-based catalysts for overall water splitting is crucial for advancing sustainable energy conversion. In this study, a novel catalyst, PBN-Ir/Mn, is reported, developed through a self-healing process of the polyhexabenzocoronene network (PBN) that incorporates both Mn and Ir atoms. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and X-ray absorption spectroscopy (XAS) characterizations confirm a unique atomic-scale Ir-Ir-Mn triangular structure on the porous PBN substrate. The synergy between Mn and Ir atoms leads to superior water electrolysis performance, with ultra-low overpotentials of 11 mV for the hydrogen evolution reaction (HER) and 220 mV for the oxygen evolution reaction (OER) at 10 mA cm-2. PBN-Ir/Mn also achieves outstanding mass activities, reaching 425.92 A mg-1 for HER and 152.28 A mg-1 OER. Moreover, PBN-Ir/Mn demonstrates exceptional durability in overall water splitting, maintaining stable performance over 100 h in a full-cell setup, surpassing commercial benchmarks. Density functional theory (DFT) calculations reveal that Mn doping modifies the d-band center of Ir, reducing the activation energy barriers and significantly enhancing both activity and stability. The high performance and stability of PBN-Ir/Mn, combined with its scalability for gram-scale synthesis, highlight its potential for industrial applications and multifunctional catalysis.

Ruthenium Clusters Modification Carbon Layer-Encapsulated NiCoP Nanoneedles as Advanced Electrocatalyst for Efficient Seawater Splitting Application

Developing efficient and durable electrocatalyst for seawater splitting is crucial in hydrogen production. Herein, a multi-scale design strategy was employed to fabricate ruthenium clusters modification carbon layer-encapsulated nickel-cobalt-phosphorus (Ru/C/NiCoP) nanoneedles electrocatalyst supported on nickel foam (NF). We demonstrated that Ru/C/NiCoP/NF exhibited exceptional oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances, with low overpotential, Tafel slope and superior stability. Furthermore, the electrocatalytic mechanism of Ru/C/NiCoP was elucidated through the combination of ex-situ and in-situ characterizations, along with comprehensive electrochemical tests. Strikingly, Ru clusters and the NiCoP with carbon layer engendered robust electronic interaction reaction, accelerated the charge transfer rate, provided more active sites, and enhanced intrinsic catalytic activity, thus substantially promoting the OER kinetics and HER reaction steps as well as stability. In addition, the two-electrode system constructed with Ru/C/NiCoP/NF achieved current density of 10 mA cm-2 in both pure water and seawater at ultra-low potential of 1.46/1.47 V, with Faraday efficiency close to 100 %. Even at higher current density of 100 mA cm-2, the required driving voltage remained low at 1.75/1.77 V, maintaining stable operation for 150 h, outperforming most reported non-noble catalysts. This innovative strategy provides facile and versatile approach for developing advanced electrocatalysts in seawater electrolysis application.

Triple Regulations via Fe Redox Boosting Nitrate Reduction to Ammonia at Industrial Current Densities

Electrochemical nitrate reduction reaction (NO3 -RR) has promising prospects for green synthesis of ammonia and environmental remediation. However, the performance of catalysts at high current density usually suffers from the high energy barrier for the nitrate (NO3 -) to nitrite (NO2 -) and the competitive hydrogen evolution. Herein, we proposed a two-step relay mechanism through spontaneous redox reaction followed electrochemical reaction by introducing low-valence Fe species into Ni2P nanosheets to significantly enhance the NO3 -RR performance at industrial current density. The existence of low-valence Fe species bypasses the NO3 - to NO2 - step through the spontaneous redox with NO3 - to produce NO2 - and Fe2O3, regulates the electronic structure of Ni2P to reduce the barrier of NO2 - to NH3, thirdly prohibits the hydrogen evolution by consuming the excess active hydrogen through reduction of Fe2O3 to recover low-valence Fe species. The triple regulations via Fe redox during the two-step relay reactions guarantee the Fe-Ni2P@NF high ammonia yield of 120.1 mg h-1 cm-2 with Faraday efficiency of more than 90% over a wide potential window and a long-term stability of more than 130 h at ~1000 mA cm-2. This work provides a new strategy to realize the design and synthesis of nitrate reduction electrocatalysts at high current densities.

Trace Amount of Ir Decorated NiFe Phosphide In-Situ Grown on Carbon Cloth as Cost-Effective Electrocatalyst for Oxygen Evolution Reaction

Cost-effective electrocatalysts is a key constituent to establish the balance of cost and catalytic efficiency for oxygen evolution reaction (OER) via water electrolysis in the area of energy conversion and storage. NiFe phosphide decorated with trace amount of iridium (Ir) species in-situ grown on carbon cloth was prepared by a facile wet chemistry approach followed by a phosphorization post-treatment at a relative low temperature. The optimal electrocatalyst, Ir2-NiFePx/CC, exhibits excellent OER activity, with an low overpotential of 190 mV at 10 mA cm-2 for alkaline OER, and a desirable long-term durability over 90 h. The outstanding OER performance stems from the structural evolution via phosphorization process, Ir decoration with more high-valence stated Ir4+ species, and tight connection between individual components of the electrode, which gives rise to the strong activity to the active sites and faster reaction kinetics in the alkaline OER process. Mover, the Ir loading was as low as approximately ~1.7 wt % (0.29 mg cm-2), showing promissing propective in cost-effective OER.

Electronic transfer and structural reconstruction in porous NF/FeNiP-CoP@NC heterostructure for robust overall water splitting in alkaline electrolytes

Multimetal phosphides derived from metal-organic frameworks (MOFs) have garnered significant interest owing to their distinct electronic configurations and abundant active sites. However, developing robust and efficient catalysts based on metal phosphides for overall water splitting (OWS) remains challenging. Herein, we present an approach for synthesizing a self-supporting hollow porous cubic FeNiP-CoP@NC catalyst on a nickel foam (NF) substrate. Through ion exchange, the reconstruction chemistry transforms the FeNi-MOF nanospheres into intricate hollow porous FeNi-MOF-Co nanocubes. After phosphorization, numerous N, P co-doped carbon-coated FeNiP-CoP nanoparticles were tightly embedded within a two-dimensional (2D) carbon matrix. The NF/FeNiP-CoP@NC heterostructure retained a porous configuration, numerous heterogeneous interfaces, distinct defects, and a rich composition of active sites. Moreover, incorporating Co and the resulting structural evolution facilitated the electron transfer in FeNiP-CoP@NC, enhancing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. Consequently, the NF/FeNiP-CoP@NC catalyst demonstrated very low overpotentials of 78 mV for OER and 254 mV for HER in an alkaline medium. It also exhibited excellent long-term stability at various potentials (@10 mA cm-2, @20 mA cm-2, and @50 mA cm-2). As an overall water splitting cell, it required only 1.478 V to drive a current density of 50 mA cm-2 and demonstrated long-term stability. Density functional theory (DFT) calculations revealed a synergistic effect between multimetal phosphides, enhancing the intrinsic OER and HER activities of FeNiP-CoP@NC. This work not only elucidates the role of heteroatom induction in structural reconstruction but also highlights the importance of electronic structure modulation.

Ir-Doped Core-Shell Hollow Heterogeneous Nanospindles for Electrocatalytic Oxygen Evolution Reaction

By utilizing Metal-organic framework (MOF) materials as a base, constructing electrocatalysts with heterogeneous structures offers advantages for catalyzing water splitting. In this study, a hollow heterogeneous nanocatalyst, Ir-MIL-88A@NiFe-LDHs, was prepared by growing a layered double hydroxides (LDHs) shell on MIL-88A substrate. The catalyst shows excellent oxygen evolution reaction (OER) performance in a 1.0 M KOH solution, requiring only 217 mV overpotential to achieve a current density of 10 mA cm-2 with a Tafel slope of 62.18 mV dec-1, indicating significant electrocatalytic performance and reaction kinetics characteristics. Furthermore, long-term OER testing also demonstrates the catalyst's outstanding stability. Emphasizing the interfacial interaction between MOF and LDHs, as well as the synergistic effect among Ni, Fe, and Ir elements, the study highlights how these factors collaboratively control the local electronic structure of the hollow Ir-MIL-88A@NiFe-LDHs, resulting in an efficient MOF-derived electrocatalyst.

Universal Synthesis of Single-Atom Catalysts by Direct Thermal Decomposition of Molten Salts for Boosting Acidic Water Splitting

Single-atom catalysts (SACs) are considered prominent materials in the field of catalysis due to their high metal atom utilization and selectivity. However, the wide-ranging applications of SACs remain a significant challenge due to their complex preparation processes. Here, a universal strategy is reported to prepare a series of noble metal single atoms on different non-noble metal oxides through a facile one-step thermal decomposition of molten salts. By using a mixture of non-noble metal nitrate and a small-amount noble metal chloride as the precursor, noble metal single atoms can be easily introduced into the non-noble metal oxide lattice owing to the cation exchange in the in situ formed molten salt, followed by the thermal decomposition of nitrate anions during the heating process. Analyses using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy confirm the formation of the finely dispersed single atoms. Specially, the as-synthesized Ir single atoms (10.97 wt%) and Pt single atoms (4.60 wt%) on the Co3O4 support demonstrate outstanding electrocatalytic activities for oxygen evolution reaction and hydrogen evolution reaction, respectively.

Reversing the Interfacial Electric Field in Metal Phosphide Heterojunction by Fe-Doping for Large-Current Oxygen Evolution Reaction

Developing non-precious-metal electrocatalysts that can operate with a low overpotential at a high current density for industrial application is challenging. Heterogeneous bimetallic phosphides have attracted much interest. Despite high hydrogen evolution reaction (HER) performance, the ordinary oxygen evolution reaction (OER) performance hinders their practical use. Herein, it is shown that Fe-doping reverses and enlarges the interfacial electrical field at the heterojunction, turning the H intermediate favorable binding sites for HER into O intermediate favorable sites for OER. Specifically, the self-supported heterojunction catalysts on nickel foam (CoP@Ni2P/NF and Fe-CoP@Fe-Ni2P/NF) are readily synthesized. They only require the overpotentials of 266 and 274 mV to drive a large current density of 1000 mA cm-2 (j1000) for HER and OER, respectively. Furthermore, a water splitting cell equipped with these electrodes only requires a voltage of 1.724 V to drive j1000 with excellent durability, demonstrating the potential of industrial application. This work offers new insights on interfacial engineering for heterojunction catalysts.

CoFeBP Micro Flowers (MFs) for Highly Efficient Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

Hydrogen is one of the most promising green energy alternatives due to its high gravimetric energy density, zero-carbon emissions, and other advantages. In this work, a CoFeBP micro-flower (MF) electrocatalyst is fabricated as an advanced water-splitting electrocatalyst by a hydrothermal approach for hydrogen production with the highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The fabrication process of the CoFeBP MF electrocatalyst is systematically optimized by thorough investigations on various hydrothermal synthesis and post-annealing parameters. The best optimized CoFeBP MF electrode demonstrates HER/OER overpotentials of 20 mV and 219 mV at 20 mA/cm2. The CoFeBP MFs also exhibit a low 2-electrode (2-E) cell voltage of 1.60 V at 50 mA/cm2, which is comparable to the benchmark electrodes of Pt/C and RuO2. The CoFeBP MFs demonstrate excellent 2-E stability of over 100 h operation under harsh industrial operational conditions at 60 °C in 6 M KOH at a high current density of 1000 mA/cm2. The flower-like morphology can offer a largely increased electrochemical active surface area (ECSA), and systematic post-annealing can lead to improved crystallinity in CoFeBP MFs.

Synergistic engineering of P, N-codoped carbon-confined bimetallic cobalt/nickel phosphides with tailored electronic structures for boosting urea electro-oxidation

Bimetallic phosphides exhibit superior electrocatalytic activities and synergistic effects that make them ideal electrocatalysts for the urea oxidation reaction (UOR). Herein, P, N-codoped carbon-encapsulated cobalt/nickel phosphides derived from NiCo-MOF-74 (NiCoP@PNC) and anchored on P-doped carbonized wood fiber (PCWF) for UOR were prepared through synchronous carbonization and phosphorization. By benefiting from the synergistic effect of structural and electronic modulation, NiCoP@PNC/PCWF exhibits excellent UOR electrocatalytic performance under alkaline conditions, achieving a current density of 50 mA cm-2 with a potential of only 1.34 V (vs reversible hydrogen electrode, RHE) and continuous operation for more than 72 h. In addition, for the overall urea splitting, an electrolyzer using UOR replaced OER, which required only 1.50 V to achieve a current density of 50 mA cm-2 with excellent stability, 230 mV less than that required for the HER||OER system. In-depth theoretical analysis further proves that the strong synergistic effect between Co and Ni optimizes electronic structures, yielding excellent UOR properties. The synergistic strategy of structural and electrical modulation provides broad prospects for the design and synthesis of excellent UOR electrocatalysts for energy-saving hydrogen production by using renewable resources.

Doping Ru on FeNi LDH/FeII/III-MOF heterogeneous core-shell structure for efficient oxygen evolution

Noble metal-based catalysts such as RuO2 and IrO2 are widely used in the catalysis of the OER. However, because of their high price and poor stability, it is urgent to develop transition metal-based electrocatalysts with low precious metal doping as an alternative. Layered double hydroxides (LDHs) grown on 3D metal-organic frameworks (MOFs) are ideal for doping precious metals owing to abundant defects at the heterointerface, large surface area, and intrinsic oxygen evolution activity. In this study, a novel FeNi LDH/MOF heterostructure was prepared via a two-step solvothermal method using Fe-soc-MOFs as the substrate. Subsequently, Ru was introduced through a hydrothermal process. The as-synthesized Ru@FeNi LDH/MOF has an overpotential of only 242 mV at a current density of 10 mA cm-2 and can be used in continuous electrolysis for 48 h. Its unique nanocubic core-shell structure and flower-like LDHs on its surface provide a large number of active sites, which become the key to ensuring high activity and stability. With the doping of Ru, the electronic structure was adjusted and electron transfer was accelerated, further improving electrochemical activity. This study provides a new idea for developing transition metal-based catalysts with low noble metal loading.

Electronic Structure Regulated Nickel-Cobalt Bimetal Phosphide Nanoneedles for Efficient Overall Water Splitting

Transition metal phosphides (TMPs) have been widely studied for water decomposition for their monocatalytic property for anodic or cathodic reactions. However, their bifunctional catalytic activity still remains a major challenge. Herein, hexagonal nickel-cobalt bimetallic phosphide nanoneedles with 1-3 μm length and 15-30 nm diameter supported on NF (NixCo2-xP NDs/NF) with adjusted electron structure have been successfully prepared. The overall alkaline water electrolyzer composed of the optimal anode (Ni0.67Co1.33P NDs/NF) and cathode (Ni1.01Co0.99P NDs/NF) provide 100 mA cm-2 at 1.62 V. Gibbs Free Energy for reaction paths proves that the active site in the hydrogen evolution reaction (HER) is Ni and the oxygen evolution reaction (OER) is Co in NixCo2-xP, respectively. In the HER process, Co-doping can result in an apparent accumulation of charge around Ni active sites in favor of promoting HER activity of Ni sites, and ΔGH* of 0.19 eV is achieved. In the OER process, the abundant electron transfer around Co-active sites results in the excellent ability to adsorb and desorb *O and *OOH intermediates and an effectively reduced ∆GRDS of 0.37 eV. This research explains the regulation of electronic structure change on the active sites of bimetallic materials and provides an effective way to design a stable and effective electrocatalytic decomposition of alkaline water.