Coupling a Low Loading of IrP2, PtP2, or Pd3P with Heteroatom-Doped Nanocarbon for Overall Water-Splitting Cells and Zinc-Air Batteries

Metallic Glass Nanoparticles Synthesized via Flash Joule Heating

Metallic glass (MG) nanoparticles have attracted intensive research interest for their promising mechanical and catalytic applications. However, current production methods lack the ability to precisely control phase, composition, and morphology, making it challenging to explicitly study their structure-property relationship. Here, we report a direct one-step synthesis of MG nanoparticles using flash Joule heating (FJH) that allows us to produce nanoparticles with desired phase, composition, and morphology. With the fast and controllable cooling attainable through FJH, we can produce fully amorphous Pd-P, Pd-Ni-P, and Pd-Cu-P nanoparticles with precise control in alloy composition and particle size (2.33 nm ± 0.83 nm). As a demonstration of potential application, we show the improved oxygen evolution activity (∼300 mV lower onset potential) of the MG nanoparticles over their crystalline counterparts and long-term stability in 60-h testing.

Creating Bridged-H* Bond Structure for Boosting Electrocatalytic Hydrogen Evolution via Phosphorus-Doped Iridium Nanosheets

Iridium (Ir) is recognized to have extremely high catalytic activity in the hydrogen evolution reaction (HER). However, there are still technical challenges in maximizing the utilization of Ir atoms in the catalytic reaction process through dimensional regulation strategies. Herein, an innovative strategy is utilized to fabricate porous phosphorus-doped iridium (P-Ir) with a 2D structure, specifically the reduction of 1T phase-IrO2 (1T-IrO2) nanosheets using phosphine gas. The optimized P-Ir achieves an overpotential of 17.2 mV (vs RHE without iR-correction) in 0.5 m H2SO4 during the HER process, outperforming benchmark Pt/C (27.0 mV) and most reported Ir-based electrocatalysts. During the long-term stability tests, P-Ir maintains stable operation for more than 100 h at both -10 and -100 mA cm-2, respectively. Moreover, the HER activity and transient potential scanning results of Ir-based phosphides prove that doping P atoms in the Ir lattice promotes the reaction kinetic rate and charge transport capacity during hydrogen evolution. Theoretical calculations reveal that P atoms doping weakens the adsorption energy of H intermediates (H*) by regulating the d-band center of the Ir sites. Simultaneously, the desorption process of H* is also facilitated by forming a special bridged-H* bond structure, eventually accelerating the HER kinetics.

Decoding the Hume-Rothery Rule in a Bifunctional Tetra-metallic Alloy for Alkaline Water Electrolysis

The 90-year-old Hume-Rothery rule was adapted to design an outstanding bifunctional tetra-metallic alloy electrocatalyst for water electrolysis. Following the radius mismatch principles, Fe (131 pm) and Ni (124 pm) are selectively incorporated at the Pd (139 pm) site of Mo0.30Pd0.70 nanosheets. Analogously, Cu (132 pm) alloys with only Pd, while Ag (145 pm) alloys with both Pd and Mo (154 pm). The face-centered cubic Mo0.30Pd0.35Ni0.23Fe0.12 nanosheets with 10-12 atomic layers, featuring in-plane compressive strain along the {111} basal plane, show 1/3 (422) reflection from local hexagonal symmetry. The more electronegative Pd attracts electron density from Ni/Fe in Mo0.30Pd0.35Ni0.23Fe0.12, synergistically boosting the mass activities for hydrogen and oxygen evolution reactions to 89 ± 5 and 38.6 ± 3.1 A g-1 at ±400 mV versus RHE, respectively. Full water electrolysis continues for ≥550 h, requiring cell voltages of 1.51 and 1.63 V at 10 and 100 mA cm-2, delivering 45 mL h-1 green H2.

Noble Metal Phosphides: Robust Electrocatalysts toward Hydrogen Evolution Reaction

Facing with serious carbon emission issues, the production of green H2 from electrocatalytic hydrogen evolution reaction (HER) has received extensive research interest. Almost all kinds of noble metal phosphides (NMPs) consisting of Pt-group elements (i.e., Ru, Rh, Pd, Os, Ir and Pt) are all highly active and pH-universal electrocatalysts toward HER. In this review, the recent progress of NMP-based HER electrocatalysts is summarized. It is further take typical examples for discussing important impact factors on the HER performance of NMPs, including crystalline phase, morphology, noble metal element and doping. Moreover, the synthesis and HER application of hybrid catalysts consisting of NMPs and other materials such as transition metal phosphides, oxides, sulfides and phosphates, carbon materials and noble metals is also reviewed. Reducing the use of noble metal is the key idea for NMP-based hybrid electrocatalysts, while the expanded functionality and structure-performance relationship are also noticed in this part. At last, the potential opportunities and challenges for this kind of highly active catalyst is discussed.

Promoting Electrocatalytic Oxygen Reactions Using Advanced Heterostructures for Rechargeable Zinc-Air Battery Applications

In order to facilitate electrochemical oxygen reactions in electrically rechargeable zinc-air batteries (ZABs), there is a need to develop innovative approaches for efficient oxygen electrocatalysts. Due to their reliability, high energy density, material abundance, and ecofriendliness, rechargeable ZABs hold promise as next-generation energy storage and conversion devices. However, the large-scale application of ZABs is currently hindered by the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of heterostructure-based electrocatalysts has the potential to surpass the limitations imposed by the intrinsic properties of a single material. This Account begins with an explanation of the configurations of ZABs and the fundamentals of the oxygen electrochemistry of the air electrode. Then, we summarize recent progress with respect to the variety of heterostructures that exploit bifunctional electrocatalytic reactions and overview their impact on ZAB performance. The range of heterointerfacial engineering strategies for improving the ORR/OER and ZAB performance includes tailoring the surface chemistry, dimensionality of catalysts, interfacial charge transfer, mass and charge transport, and morphology. We highlight the multicomponent design approaches that take these features into account to create advanced highly active bifunctional catalysts. Finally, we discuss the challenges and future perspectives on this important topic that aim to enhance the bifunctional activity and performance of zinc-air batteries.

Interfacial Engineering of Polycrystalline Pt5 P2 Nanocrystals and Amorphous Nickel Phosphate Nanorods for Electrocatalytic Alkaline Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is important for hydrogen economy but suffers from sluggish reaction kinetics due to a large water dissociation energy barrier. Herein, Pt₅ P₂ nanocrystals anchoring on amorphous nickel phosphate nanorods as a high-performance interfacial electrocatalyst system (Pt₅ P₂ NCs/a-NiPi) for the alkaline HER are demonstrated. At the unique polycrystalline/amorphous interface with abundant defects, strong electronic interaction, and optimized intermediate adsorption strength, water dissociation is accelerated over abundant oxophilic Ni sites of amorphous NiPi, while hydride coupling is promoted on the adjacent electron-rich Pt sites of Pt₅ P₂ . Meanwhile, the ultra-small-sized Pt₅ P₂ nanocrystals and amorphous NiPi nanorods maximize the density of interfacial active sites for the Volmer-Tafel reaction. Pt₅ P₂ NCs/a-NiPi exhibits small overpotentials of merely 9 and 41 mV at -10 and -100 mA cm^-2 in 1 M KOH, respectively. Notably, Pt₅ P₂ NCs/a-NiPi exhibits an unprecedentedly high mass activity (MA) of 14.9 mA µg_Pt ^-1 at an overpotential of 70 mV, which is 80 times higher than that of Pt/C and represents the highest MA of reported Pt-based electrocatalysts for the alkaline HER. This work demonstrates a phosphorization and interfacing strategy for promoting Pt utilization and in-depth mechanistic insights for the alkaline HER.

Electronic and Potential Synergistic Effects of Surface-Doped P-O Species on Uniform Pd Nanospheres: Breaking the Linear Scaling Relationship toward Electrochemical Oxygen Reduction

Developing efficient oxygen reduction reaction (ORR) electrocatalysts is critical to fuel cells and metal-oxygen batteries, but also greatly hindered by the limited Pt resources and the long-standing linear scaling relationship (LSR). In this study, ∼6 nm and highly uniform Pd nanospheres (NSs) having surface-doped (SD) P-O species are synthesized and evenly anchored onto carbon blacks, which are further simply heat-treated (HT). Under alkaline conditions, Pd/^SDP-O NSs/C-HT exhibits respective 8.7 (4.3)- and 5.0 (5.5)-fold enhancements in noble-metal-mass- and area-specific activity (NM-MSA and ASA) compared with the commercial Pd/C (Pt/C). It also possesses an improved electrochemical stability. Besides, its acidic ASA and NM-MSA are 2.9 and 5.1 times those of the commercial Pd/C, respectively, and reach 65.4 and 51.5% of those of the commercial Pt/C. Moreover, it also shows nearly ideal 4-electron ORR pathways under both alkaline and acidic conditions. The detailed experimental and theoretical analyses reveal the following: (1) The electronic effect induced by the P-O species can downshift the surface d-band center to weaken the intermediate adsorptions, thus preserving more surface active sites. (2) More importantly, the potential hydrogen bond between the O atom in the P-O species and the H atom in the hydrogen-containing intermediates can in turn stabilize their adsorptions, thus breaking the ORR LSR toward more efficient ORRs and 4-electron pathways. This study develops a low-cost and high-performance ORR electrocatalyst and proposes a promising strategy for breaking the ORR LSR, which may be further applied in other electrocatalysis.

Layered FeCoNi double hydroxides with tailored surface electronic configurations induced by oxygen and unsaturated metal vacancies for boosting the overall water splitting process

Two-dimensional (2D) layered double hydroxides (LDH) with excellent hydrophilic ability and rapid hydroxyl insertion are regarded as one of the most promising electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) for overall water splitting to produce hydrogen. However, the electrocatalytic HER/OER activities can be restricted by the inert basal plane due to the poor conductivity, deficient active sites and inferior durability despite there being efficient active sites in the material edge. Thus, capturing many more exposed reactive sites to facilitate the rapid reaction kinetics is a crucial strategy. In this paper, both oxygen and unsaturated metal vacancies with FeCoNi LDH materials are generated through a surface activation approach by pre-covering of fluoride and a post-boronizing process. Such a material is grown on Ni foam to form an F-FeCoNi-Ov LDH/NF electrocatalyst. The activated surface of the electrocatalyst with oxygen vacancies and unsaturated metal sites shows enhanced electroconductivity for regulating the surface electronic structure and optimizing the surface adsorption energy for intermediates during HER/OER processes. As a result, this electrocatalyst exhibits excellent electrocatalytic performance for both the HER and OER with low overpotentials, small Tafel slopes and long durability. The enhancement mechanism is also studied deeply for fundamental understanding. For performance validation, an F-FeCoNi-Ov LDH/NF∥F-FeCoNi-Ov LDH/NF water splitting cell is fabricated and needs only 1.54 V and 1.81 V to reach current densities of 10 and 100 mA cm^-2, respectively. This work provides a practicable strategy to develop 2D LDH nanomaterials with boosted electrocatalytic activity for sustainable and clean energy storage systems.

Boosting the anti-poisoning ability of palladium towards electrocatalytic formic acid oxidation via polyphosphide chemistry

In this work, we reported a novel polyphosphide strategy for the synthesis of phosphorus doped Pd (P-Pd) using red phosphorus as the starting material at quasi-ambient conditions. Polyphophide anions, as the key reaction intermediates, served as the reducing agent and phosphorus source to modulate the surface electronic structure of Pd. The P-Pd obtained exhibited topmost CO tolerance and electrocatalytic activity to formic acid oxidation among the state-of-arts reports. The mass activity and turnover frequency of P-Pd reached 4413 mA mg^-1_Pd and 16.04 s^-1 at 0.8 V, which were 23.7 and 6.4 times that of commercial Pd/C respectively. After 1000 repeated cycles, 82% initial activity was reserved. Combined with the electrochemical analysis and the density functional theory calculation, the boosted electrochemical performances can be attributed to the size and electronic effects induced by the P doping, which increase the surface actives sites, inhibit the adsorption of CO and change the reaction pathway to favorable CO₂ route. A full cell was also assembled to demonstrate the practical potential of the P-Pd, which showed a maximum power density of 21.56 mW cm^-2. This polyphophide-based reaction route provides a new strategy for the preparation of efficient and durable phosphorus doped alloys for electrocatalysis.

Robust Visible-Blind Wearable Infrared Sensor Based on IrP2 Nanoparticle-Embedded Few-Layer Graphene and the Effect of Photogating

It is challenging to realize a visible-blind infrared photodetector as the materials that absorb infrared light also absorb visible light. Here, we report the synthesis of IrP₂ nanoparticle-embedded few-layer graphene by one-step solid-state pyrolysis and its application in visible-blind infrared sensing. A linear photodetector device was fabricated by drop casting IrP₂ nanoparticle-embedded few-layer graphene onto a flexible PET substrate with two gold electrodes separated by ∼16 μm. The photoconductive gain was found to be as high as ∼145% with response and decay times of ∼0.4 and ∼2.8 s, respectively, under 1550 nm irradiation of 800 mW cm^-2. The room-temperature responsivity was ∼1.81 A W^-1 at 80 mW cm^-2 and ∼0.54 A W^-1 at a high incident power of ∼2200 mW cm^-2 under a bias of 1 V. Interestingly, the device showed response even in the long-wavelength infrared region, but no response was found under visible light. The embedded IrP₂ nanoparticles act as trap centers inducing photogating in the device, and the average trap state energy was estimated to be ∼16.5 ± 1.5 meV from the temperature-dependent photocurrent studies. The device was found to be immune to air exposure and bending, suggestive of use a a wearable sensor.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂ RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

An FexNi4−xPy/N, P co-doped carbon nanotube composite as a bifunctional electrocatalyst for oxygen and hydrogen electrode reactions

The Fe_xNi_4−xP_y/N, P-CNT complex exhibits excellent bifunctional catalytic performance towards HER and OER due to the synergy of high electrical conductivity, multicomponent active sites, and anchoring effect of carbon nanotubes.

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR

Efficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm-2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

Polyaniline/Pure Carbon Assemblies as Efficient Self-standing Metal-free Oxygen Electrodes in Alkaline Media for Zn-Air Batteries

A facile design and fabrication of self-standing metal-free polyaniline (PANI)@carbon nanotubes (CNTs) composite membrane was initially proposed by straightforward noncovalent wrapping the polymer around pure CNTs. Without introduction of extra heteroatoms into CNTs, the optimized PANI@CNTs composite exhibits a much better electrocatalytic performance for oxygen evolution reaction (OER) than pure CNTs via favorable interfacial modification with PANI to largely expose the active sites of on the surface of pure CNTs. Besides, it displays good oxygen reduction reaction (ORR) performance. When directly utilized as bifunctional air electrode without extra additive agents, the composite membrane-enabled rechargeable Zn-air batteries not only deliver a high peak power density (201.9 W g^-1 ) and a large energy density (850.3 Wh kg_Zn ^-1 ), but also present robust cycling performance for 216 cycles with a high energy efficiency of 57.8%.

Versatile Route To Fabricate Precious-Metal Phosphide Electrocatalyst for Acid-Stable Hydrogen Oxidation and Evolution Reactions

Highly active catalyst for the hydrogen oxidation/evolution reactions (HOR and HER) plays an essential role for the water-to-hydrogen reversible conversion. Currently, increasing attention has been concentrated on developing low-cost, high-activity, and long-life catalytic materials, especially for acid media due to the promise of proton exchange membrane (PEM)-based electrolyzers and polymer electrolyte fuel cells. Although non-precious-metal phosphide (NPMP) catalysts have been widely researched, their electrocatalytic activity toward HER is still not satisfactory compared to that of Pt catalysts. Herein, a series of precious-metal phosphides (PMPs) supported on graphene (rGO), including IrP₂-rGO, Rh₂P-rGO, RuP-rGO, and Pd₃P-rGO, are prepared by a simple, facile, eco-friendly, and scalable approach. As an example, the resultant IrP₂-rGO displays better HER electrocatalytic performance and longer durability than the benchmark materials of commercial Pt/C under acidic, neutral, and basic electrolytes. To attain a current density of 10 mA cm^-2, IrP₂-rGO shows overpotentials of 8, 51, and 13 mV in 0.5 M dilute sulfuric acid, 1.0 M phosphate-buffered saline (PBS), and 1.0 M potassium hydroxide solutions, respectively. Additionally, IrP₂-rGO also exhibits exceptional HOR performance in the 0.1 M HClO₄ medium. Therefore, this work offers a vital addition to the development of a number of PMPs with excellent activity toward HOR and HER.

FexNiy/CeO2 loaded on N-doped nanocarbon as an advanced bifunctional electrocatalyst for the overall water splitting

The synergy of each component in the Fe_xNi_y/CeO₂/NC renders outstanding electrocatalytic activities and stability toward the HER and OER.