Overall Water Splitting Research Articles

Molecular Engineering of Methylated Sulfone-Based Covalent Organic Frameworks for Back-Reaction Inhibited Photocatalytic Overall Water Splitting.

Solar-to-hydrogen (H2) and oxygen (O2) conversion via photocatalytic overall water splitting (OWS) holds great promise for a sustainable fuel economy, but has been challenged by the backward O2 reduction reaction (ORR) with favored proton-coupled electron transfer (PCET) dynamics. Here, we report that molecular engineering by methylation inhibits the backward ORR of molecular photocatalysts and enables efficient OWS process. As demonstrated by a benchmark sulfone-based covalent organic framework (COF) photocatalyst, the precise methylation of its O2 adsorption sites effectively blocks electron transfer and increases the barrier for hydrogen intermediate desorption that cooperatively obstructs the PCET process of ORR. Methylation also repels electrons to the neighboring photocatalytic sulfone group that promotes the forward H2 evolution. The resultant DS-COF achieves an impressive inhibition of about 70 % of the backward reaction and a three-fold enhancement of the OWS performance with a H2 evolution rate of 124.7 μmol h-1 g-1, ranking among the highest reported for organic-based photocatalysts. This work provides insights for engineering photocatalysts at the molecular level for efficient solar-to-fuel conversion.

Design and construction of 3D porous hierarchical structure Ni–Fe–Co bifunctional catalyst toward highly efficient overall water splitting

Developing high performance, cost-effective, non-precious metal electrocatalysts for overall water splitting (OWS) still remains a serious challenge. Heterostructures comprised of multiple metals possess significant potential to enhance OWS owing to the prominent synergistic effects between different components. Herein, we successfully fabricated NiFeCoPSO and Co(OH)2/NiFeSO structures with a three-dimensional (3D) porous hierarchical structure, using carbon cloth (CC) as a substrate. The innovative 3D hierarchical structure ensures that numerous active sites are extensively exposed, thus guaranteeing competent contact between the active reaction centers and the reactant. As a result, the obtained NiFeCoPSO displays outstanding hydrogen evolution reaction (HER) ability (102 mV for a current density of 10 mA cm−2), while the intermediate product Co(OH)2/NiFeSO exhibits excellent oxygen evolution reaction (OER) performance (231 mV for 10 mA cm−2). Furthermore, the dual electrode system assembled using NiFeCoPSO cathode and Co(OH)2/NiFeSO anode presents excellent overall water splitting (OWS) behavior (1.55 V for 10 mA cm−2). This research offers a cost-effective transition metal phosphide-sulfide electrocatalyst and its synthesis method for OWS.

Fe‐Based Materials for Electrocatalytic Water Splitting: A Mini Review

AbstractIn the last few years, the development of effective electrocatalysts hold fascinating importance towards scalable green hydrogen (H2) and oxygen (O2) production has become an appealing area of research. A good number of iron‐based catalysts have been designed and synthesized which can mediate water splitting under mild conditions with minimum energy requirements. In this review, recent progress on iron‐based electrocatalysts focusing on Oxygen Evolution Reaction (OER), Hydrogen Evolution Reaction (HER), and Overall Water Splitting (OWS) are summarized. Tactical designing, targeted synthesis with electronic tuning, efficiency as well as durability are discussed here. The review is comprehensive and our target is to promote the development of highly efficient economical catalysts, to make their way from the laboratory to market by replacing noble metal‐based electrocatalysts.

Enriched edge sites of ultrathin Ni3S2/NiO nanomeshes promote surface reconstruction for robust electrochemical water splitting

Developing highly efficient nonnoble bifunctional electrocatalysts for both the H2 evolution reaction (HER) and O2 evolution reaction (OER) is essential but challenging for overall water splitting (OWS). Ni based catalysts are proved as promising candidates for water splitting, which usually undergo surface reconstruction by transforming into nickel oxyhydroxides as active sites. Although evidence suggests that the reconstruction originates from the exchange of surface lattice oxygen with the OH- in the electrolyte under electric field, modulating the reconstruction of Ni based catalysts remains a great challenge. Herein, we propose an edge sites enrichment strategy to promote the active phase evolution. The one-step synthesized ultrathin Ni3S2/NiO nanomeshes exhibited an ultrathin porous structure which contain abundant edge sites and Ni3S2/NiO in-plane interface sites. Owing to the unique structure, Ni3S2/NiO nanomeshes possessed an affinity feature to proton and OH-, resulting in a faster reconstruction from Ni3S2 to Ni(OH)2 than Ni3S2 bulk which subsequently converted into γ-NiOOH and a lower adsorption barrier for H*. Consequently, the Ni3S2/NiO nanomeshes exhibited outstanding OER activity (300 mV at 200 mA cm−2) and unexpected HER activity (73 mV at 10 mA cm−2) in 1.0 M KOH. Remarkably, the nanomeshes achieved an ultralow voltage of 1.41 V at 10 mA cm−2 with excellent stability for overall water splitting, which prevailed over most of the reported catalysts. Moreover, the nanomeshes performed a H2 yield of 900 µmol/h in a solar-assisted water splitting system with a H2 minimum sales price of $1.77/kg, much lower than that of the commercial catalyst ($7.18/kg). This work sets a new benchmark of monometallic bifunctional catalysts for industrial water splitting and provides new insights into the synthesis of 2D nanomeshes.

A Multi‐Active Site Subnano Heterostructures Catalyst Grown In situ POM and Fe0.2Ni0.8Co2O4 onto Nickel Foam Toward Efficient Electrocatalytic Overall Water Splitting

AbstractDesigning efficient, durable, and cheap bifunctional electrocatalysts is a challenging goal in water splitting. Herein, trivanadium‐substituted Keggin‐type polyoxometalate H6PV3Mo9O40 (POM) and Fe0.2Ni0.8Co2O4 (FNCO) are in situ grown onto nickel foam (NF) yielding a self‐supporting nanoflower‐like heterojunction via convenient hydrothermal reaction. The POM‐Fe0.2Ni0.8Co2O4/NF as HER and OER electrocatalyst, displays low overpotential (89 and 259 mV) and high electrode stability at 10 mA cm−2. POM‐FNCO/NF as the cathode and anode requires a lower voltage (1.58 V) to provide 10 mA cm−2 for overall water splitting (OWS), which is better than that of commercial catalysts. The electronic sponge characteristics of POM provide more active sites and fast reaction kinetics for HER and OER. The synergy of POM and FNCO optimizes the electron distribution at the interface and enhances the intrinsic activity of HER/OER. Density Functional Theory (DFT) calculations show that water molecules preferentially bind to Co sites on POM‐FNCO. Additionally, POM has proton‐coupled electron transfer properties and its modified FNCO exhibits thermodynamic advantages. The synergistic effect of these two factors enables the efficient overall water splitting of POM‐FNCO. This study offers a novel pathway for the construction of self‐supporting efficient catalysts by in situ growth of POM nanoclusters and spinel oxide sub‐nanometer heterojunctions on NF.

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.

Revealing the Electro-oxidation Mechanism of 5-Aminotetrazole on Nickel-Based Oxides and Synthesizing 5,5'-Azotetrazolate Salts.

With the gradual expansion of the application of organic electromechanical synthesis in the field of energetic materials, it is necessary to explore deeply the mechanisms behind the organic electromechanical oxidation of energetic materials in order to develop efficient electrocatalysts. Electrochemical synthesis of 5,5'-azotetrazolate (ZT) salts is not only environmentally friendly and efficient but also can replace oxygen evolution reaction (OER) combined with hydrogen production, significantly reducing the battery voltage of overall water splitting (OWS) and achieving low energy consumption hydrogen production. Here, we prepared the Co-modified nickel-based oxide electrodes (Ni3-xCoO4/carbon cloth (CC), x = 1, 2) as a medium to reveal the oxidative coupling mechanism of 5-aminotetrazole (5-AT). Experimental and theoretical calculations verified that Ni-catalyzed oxidative coupling of 5-AT is a proton-coupled electron transfer (PCET) process, including electron transfer of electrocatalytic intermediates (Ni2+-O + OH- = Ni3+-O(OH) + e-) and spontaneous dehydrogenation process (Ni3+-O(OH) + X-H = Ni2+-O + X•). The Ni3+-O(OH) is an extremely fast nonreducing electron transfer center that serves as a chemical oxidant to directly abstract hydrogen atoms from the 5-AT. Simultaneously, the synergistic effect of Co doping on the electric cloud around Ni causes the upshift of the d-band centers, which is conducive to the easier adsorption of OH*, forming the generation of active intermediate Ni3+-O(OH). Thus, Ni2CoO4/CC has higher Faraday efficiency (FE) and yield for the oxidation reaction of 5-AT, with a yield of approximately 72.3% after electrolysis at 1.7 V vs reversible hydrogen electrode (RHE).

Rapid Electronic Transport Channel of Co‐P with Mo in a Heterostructure Embedded with P, N Dual Doped Porous Carbon for Electrocatalytic Oxygen and Hydrogen Evolution

AbstractWe developed a molybdenum (Mo)‐doped cobalt (Co)‐heterostructure embedded on a phosphorous (P) and nitrogen (N) dual‐doped porous carbon which exhibits an intrinsic electronic transport channel of Co to Mo and P. The P,Mo,O−Co/PNC/NF (NF=Nickel foam) electrode offers 335 mV overpotential at 10 mA cm−2 in OER as compared with PMA‐ZIF67‐NC/NF and ZIF67‐NC/NF electrode with an overpotential of 357 and 373 mV respectively. Linear sweep voltammetry (LSV) of overall water splitting (OWS) supports that the current density gradually increased at a cell potential of 1.6 V with a maximum of 40 mA with a corresponding cell potential of 1.79 V at a current density of 10 mA cm−2. Density functional theory (DFT) calculations for water adsorption on optimized [111] surface of Co, CoMo, and CoMoP2 with adsorbed H2O and corresponding lattice determine the electron density difference of [111] surface with adsorbed H2O for Eads (eV) 4.23 corresponds to adsorption energy for CoMoP2. XANE‐EXAFS spectroscopy of P,Mo,O−Co/PNC at Co K edge and Mo K edge suggests the presence of higher valence of both Cox+ and Mox+ without metallic Co and Mo and Co−P and Mo−P bonds as major structural units due to phosphidation as determined by R‐space FT‐EXAFS spectra.

Customized Electronic Modulations of Transition Metal Chalcogenide Electrodes Via Heterointerfacing/High‐Valence Doping Toward High‐Performance Water Electrolysis with Ampere‐Level Current Density

AbstractElectrochemical water splitting offers an advancing approach to producing highly pure hydrogen and oxygen, motivated by the prevalence of a low‐carbon economy and the goal of a sustainable future. The customized modulation of electronic structures enables the electrocatalyst to directionally promote hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which is a promising shortcut to overall water splitting (OWS). Herein, 3D homologous WSeS/CoSeS heterojunction nanoarrays (WSeS/CoSeS NAs) and W‐doped CoSeS nanoarrays (W‐CoSeS NAs) are investigated. Abundant heterointerfaces within WSeS/CoSeS NAs facilitate HER kinetics, boosting mass diffusivity, and increasing carrier separation and transfer process. High‐valence W6+ doping into CoSeS prevents phase separation and stabilizes Co sites by charge offset effect, leading to enhanced OER. Consequently, the WSeS/CoSeS NAs and W‐CoSeS NAs reach 10 mA cm−2 at an overpotential of 43.8 and 233.3 mV in 1.0 m KOH electrolyte for HER and OER, respectively. Moreover, when asymmetrically engaged as an electrolyzer, this configuration exhibits extraordinary electrocatalytic performances (cell voltage of 1.51 V at 10 mA cm−2) with satisfying stability and mechanical robustness (over 1000 h at 1000 mA cm−2). The modulation and manufacture of reaction‐property‐oriented materials are experimentally and theoretically validated potential, illuminating the light of inspiration for multiple applications.

One-step electrodeposition synthesis of NiFePS on carbon cloth as self-supported electrodes for electrochemical overall water splitting

Electrocatalytic water splitting (EWS) for hydrogen production is considered an ideal strategy for utilizing renewable energy, reducing fossil fuel consumption, and addressing environmental pollution issues. Traditional noble metal electrocatalysts have excellent performance, but their cost is high. Developing efficient, stable, and relatively inexpensive dual functional electrocatalysts is crucial for promoting large-scale EWS hydrogen production processes. Herein, a simple one-step electrodeposition method was used to grow nickel–iron phosphorus-sulfides (NiFePS) on the surface of hydrophilic treated carbon cloth (CC). The resultant NiFePS/CC with a phosphorus to sulfur ratio of 1:4 exhibited the best electrocatalytic performance, requiring only −91 mV and 216 mV overpotentials to generate the current densities of 10 mA·cm−2 in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. When it was used as a bifunctional electrocatalyst to overall water splitting (OWS), a voltage of 1.536 V can generate a current density of 10 mA·cm−2. The excellent electrocatalytic performance can be ascribed to two factors: 1) the CC with excellent conductivity serves as a growth substrate, reducing the impedance of charge transfer from the electrode to the electrolyte and accelerating the electron transfer rate; 2) The large number of ultra-thin nanosheets formed on the surface of the catalyst increase the electrochemical specific surface area, expose more reaction sites, and thus improve the electrocatalytic reaction performance. This work provides a new approach for designing efficient non-noble metal electrocatalysts for water splitting.

Wood-Structured Nanomaterials as Highly Efficient, Self-Standing Electrocatalysts for Water Splitting.

Electrocatalytic water splitting (EWS) driven by renewable energy is widely considered an environmentally friendly and sustainable approach for generating hydrogen (H2), an ideal energy carrier for the future. However, the efficiency and economic viability of large-scale water electrolysis depend on electrocatalysts that can efficiently accelerate the electrochemical reactions taking place at the two electrodes. Wood-derived nanomaterials are well-suited for serving as EWS catalysts because of their hierarchically porous structure with high surface area and low tortuosity, compositional tunability, cost-effectiveness, and self-standing integral electrode configuration. Here, recent advancements in the design and synthesis of wood-structured nanomaterials serving as advanced electrocatalysts for water splitting are summarized. First, the design principles and corresponding strategies toward highly effective wood-structured electrocatalysts (WSECs) are emphasized. Then, a comprehensive overview of current findings on WSECs, encompassing diverse structural designs and functionalities such as supported-metal nanoparticles (NPs), single-atom catalysts (SACs), metal compounds, and heterostructured electrocatalysts based on engineered wood hosts are presented. Subsequently, the application of these WSECs in various aspects of water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting (OWS), and hybrid water electrolysis (HWE) are explored. Finally, the prospects, challenges, and opportunities associated with the broad application of WSECs are briefly discussed. This review aims to provide a comprehensive understanding of the ongoing developments in water-splitting catalysts, along with outlining design principles for the future development of WSECs.

Built-in electric field and core-shell structure of the reconstructed sulfide heterojunction accelerated water splitting

The rational design of high-performance bifunctional electrocatalysts for overall water splitting (OWS) is the key to popularize hydrogen production technology. The active metal oxyhydroxide (MOOH) formed after surface self-reconfiguration of transition metal sulfide (TMS) electrocatalyst is often regarded as the "actual catalyst" in oxygen evolution reaction (OER). Herein, an Fe doped CoS2/MoS2 hollow TMS polyhedron (Fe-CoS2/MoS2) with rich Mott-Schottky heterojunction is reported and directly utilized as an OWS electrocatalyst. The spontaneous built-in electric field (BEF) at the heterogeneous interface regulates the electronic structure and D-band center of the catalyst. More importantly, the “TMS-MOOH” core-shell structure obtained in the KOH electrolyte shows enhanced OER properties. And the introduction of Fe ions activates the inert basal plane of MoS2, which greatly steps up the performance of HER. Hence, the preferable Fe-CoS2/MoS2–400 presents superior OER activity (η10 = 178 mV, η100 = 375 mV), HER activity (η10 = 92 mV) and ultra-high stability for 50 h. This work has deeply explored the catalytic mechanism of TMS and provided a new idea for the construction of efficient bifunctional catalysts.

Hollow SrTiO3 photocatalyst with spatially separated OER and HER cocatalysts for photocatalytic overall water splitting

Overcoming the challenge of sluggish charge separation and the concurrent occurrence of overall water splitting (OWS) half reactions at the same catalytic sites is crucial for achieving efficient photocatalysis. This issue often leads to a high recombination rate and the back reaction of OWS. In this study, we addressed this challenge by enhancing interfacial spatial charge separation. Specifically, we designed hollow SrTiO3 spheres and spatially segregated the hydrogen and oxygen evolution sites on the outer and inner surfaces, respectively, for OWS. The spatially distributed Pt/SrTiO3/CoOx catalysts exhibited exceptional separation of photogenerated charges, resulting in 3-times higher stoichiometric OWS compared to Pt/SrTiO3. This work underscores the effectiveness of a well-tailored spatially distributed structure in promoting charge separation in photocatalysis, thereby opening avenues for the development of efficient artificial photosynthesis systems.

Carbon Nanotubes as a Solid-State Electron Mediator for Visible-Light-Driven Z-Scheme Overall Water Splitting.

So-called Z-scheme systems, which typically comprise an H2 evolution photocatalyst (HEP), an O2 evolution photocatalyst (OEP), and an electron mediator, represent a promising approach to solar hydrogen production via photocatalytic overall water splitting (OWS). The electron mediator transferring photogenerated charges between the HEP and OEP governs the performance of such systems. However, existing electron mediators suffer from low stability, corrosiveness to the photocatalysts, and parasitic light absorption. In the present work, carbon nanotubes (CNTs) were shown to function as an effective solid-state electron mediator in a Z-scheme OWS system. Based on the high stability and good charge transfer characteristics of CNTs, this system exhibited superior OWS performance compared with other systems using more common electron mediators. The as-constructed system evolved stoichiometric amounts of H2 and O2 at near-ambient pressure with a solar-to-hydrogen energy conversion efficiency of 0.15%. The OWS reaction was also promoted in the case that this CNT-based Z-scheme system was immobilized on a substrate. Hence, CNTs are a viable electron mediator material for large-scale Z-scheme OWS systems.

CoFe(OH)x-Co3O4/NF as highly efficient electrocatalyst for oxygen evolution and urea oxidation reactions at high current densities

The advancement of an affordable and highly effective catalyst for the oxygen evolution reaction (OER) is essential to enhance the performance of overall water splitting (OWS). Here, we report a highly efficient nickel foam (NF)-supported CoFe(OH)x-Co3O4/NF heterostructure catalyst for OER. The CoFe(OH)x-Co3O4/NF heterostructure catalyst contain amorphous phase CoFe(OH)x and crystalline Co3O4, and the synergistic interaction between the two different phases reduces the charge transfer resistance, accelerates the kinetic processes of electrocatalysis and makes the catalysts exhibit excellent catalytic performance. In 1.0 M KOH solution, an overpotential (η) of merely 262 mV is needed to attain a current density of 100 mA cm−2. Even at high current densities demanded for commercial applications, the overpotentials remain very low (η500 = 291 mV, η1000 = 319 mV). The catalytic activity of CoFe(OH)x-Co3O4/NF has exceeded that of most non-noble metal OER catalysts documented in the literature. Furthermore, the CoFe(OH)x-Co3O4/NF catalyst demonstrates superior catalytic stability to OER, with only a 23 mV potential increase after 24 h of stability testing at a high current density of 500 mA cm−2. Owing to the heterostructure, the CoFe(OH)x-Co3O4/NF catalyst also exhibits excellent catalytic performance for the urea oxidation reaction (UOR), and the use of UOR instead of OER at the anode of OWS significantly reduces the cell voltage, thereby reducing the electrolytic energy consumption. The findings in this work offer precious insights into the design of OWS anode catalysts and their important applications in industrial water electrolysis. These insights are crucial for advancing the development of highly efficient and sustainable water electrolysis processes, which is essential for the production of green hydrogen and other valuable chemicals.

WO3-x as an activation medium to prompt overall water splitting of NiFe-based electrocatalyst

The efficient oxygen evolution reaction (OER) is crucial for various electrochemical processes, especially for overall water splitting (OWS). In this study, we focus on the utilization of WO3-x as an activation medium to enhance the OER performance of NiFe-based electrocatalysts. Firstly, we synthesize WO3-x nanowires supported on nickel foam (NF) and then incorporate NiFe on WO3-x nanowires by a simple hydrothermal method. The WO3-x self-supported NiFe (Oxy)hydroxide (denoted as NiFe-W-O/NF) shows a three-dimensional stereostructure composed of ultrathin nanosheets (∼ 4.0 nm). This unique structure provides a large open surface for fuller diffusion of the electrolyte while exposing more active sites. The electronic interaction of tri-centers of NiFeW accelerates the surface reconstruction process of γ-NiOOH and FeOOH, which are converted into the main active species in a short time. The electrochemical measurements confirm that the NiFe-W-O/NF has low OER overpotentials (233 mV at 10 mA cm−2, 298 mV at 100 mA cm−2) and excellent stability (100 h in total) in 1 M KOH electrolyte. In addition, the NiFe-W-O/NF || NiFe-W-O/NF battery also exhibits a low cell voltage (1.52 V at 10 mA cm−2) with a stable lifetime (50 h) under alkaline conditions. These results highlight the great potential of NiFe-W-O/NF for practical applications.

Oxygen-Deficient FeNbO4-x In-Situ Growth in Honey-Derived N-Doping Porous Carbon for Overall Water Splitting.

It is still a great challenge to reasonably design green, low cost, high activity and good stability catalysts for overall water splitting (OWS). Here, we introduce a novel catalyst with ferric niobate (FeNbO4) in-situ growing in honey-derived porous carbon of high specific surface area, and its catalytic activity is further enhanced by micro-regulation (oxygen vacancy and N-doping). From the experimental results and density functional theory (DFT) calculations, the oxygen vacancy in catalyst FeNbO4-x@NC regulates the local charge density of active site, thus increasing conductivity and optimizing hydrogen/oxygen species adsorption energy. FeNbO4 in-situ grows within N-doping honey-derived porous carbon, which can enhance active specific surface area exposure, strengthen gaseous substances escape rate, and accelerate electrons/ions transfer and electrolytes diffusion. Moreover, in-situ Raman also confirms O-species generation in oxygen evolution reaction (OER). As a result, the catalyst FeNbO4-x@NC shows good electrochemical performance in OER, HER and OWS.

Phosphorus-doped nickel cobalt oxide (NiCo2O4) wrapped in 3D hierarchical hollow N-doped carbon nanoflowers as highly efficient bifunctional electrocatalysts for overall water splitting

Properly design and fabricate capable electrocatalysts with 3D hierarchical hollow framework to realize cost-effective and efficacious overall water splitting (OWS) are particularly meaningful for the large-scale arrangement of pivotal energy technology. In this study, P-doped NiCo2O4 nanoparticles encapsulated in N-doped carbon hierarchical hollow nanoflowers (P-NiCo2O4@NCHHNFs) were constructed using the hydrothermal-pyrolysis-phosphorization approach. This fascinating architecture can not merely serve as a conductive pathway for electron transfer, but at the same time effectively inhibited the aggregation and corrosion of the NiCo2O4 nanoparticles. Additionally, the P doping not only regulates electronic structure configuration to boost the intrinsic activity of the catalyst, but also enhance electrochemical surface areas to reveal more accessible active sites. Attributing to these characteristics, the as-prepared P-NiCo2O4@NCHHNFs exhibit preeminent electrocatalytic performance with low overpotentials of 283 mV and 162 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) (at 10 mA cm−2), respectively. Specifically, by using the P-NiCo2O4@NCHHNFs as bifunctional catalysts, a low potential of 1.56 V (at 10 mA cm−2) is sufficient to drive overall water splitting with splendid durability. This study proposed an innovative strategy for the conceiving and fabricating high-performance catalysts via heteroatom-doping.

Infrared light driven overall water vapor splitting on a plasmonic semiconductor p-n heterojunction photocatalyst

Photocatalytic overall water splitting (OWS) has yet to be realized on plasmonic semiconductor photocatalysts. In this work, we reported a plasmonic heterojunction of p-Cu1.81S/n-CdS with homogeneously distributed p-type and n-type domains in a single nanoparticle. The plasmonic heterojunction displays a strong localized surface plasmon resonance (LSPR) absorption peak at 1480 nm and can drive the OWS into hydrogen and oxygen under infrared light (IR) irradiation. The IR light-induced hot electrons and holes in Cu1.81S nanodisks alone can split water vapor into hydrogen and oxygen, but with poor efficiency. Surprisingly, the plasmonic p-Cu1.81S/n-CdS heterojunction shows significantly improved IR light-driven OWS performance. Under the irradiation of IR light (λ > 800 nm), the hydrogen and oxygen production rates were 0.73 mmol gcat−1 h−1 and 0.33 mmol gcat−1 h−1, respectively. The heterojunction photocatalyst delivered a solar-to-hydrogen conversion efficiency (STH) of 0.02 % under AM 1.5G irradiation. The present study has demonstrated that plasmonic semiconductors are promising photocatalysts for harvesting IR light for green hydrogen generation.

Regulating Mo-based alloy-oxide active interfaces for efficient alkaline hydrogen evolution assisted by hydrazine oxidation

Improving the efficiency of overall water splitting (OWS) is crucial due to the slow four-electron transfer process in the oxygen evolution reaction (OER). The coupling of the thermodynamically favorable hydrazine oxidation reaction (HzOR) with the hydrogen evolution reaction (HER) significantly boosts hydrogen production. A Ru-decorated MoNi/MoO2 micropillar (Ru-MoNi/MoO2) has been synthesized using a hydrothermal followed by reduction annealing. Benefiting from Ru moderating the active interface of Mo-based alloys/oxides and the unique one-dimensional micropillar morphology. The synthesized Ru-MoNi/MoO2 exhibits outstanding bifunctional activity for HER and HzOR, achieving 10 mA cm−2 at merely −13 mV and −34 mV in 1 M KOH and 1 M KOH + 0.5 M N2H4, respectively. Notably, with Ru-MoNi/MoO2 in a dual-electrode setup, only 0.57 V is needed to achieve 50 mA cm−2, demonstrating good stability and facilitating hydrazine-assisted water splitting (OHzS). This work offers insights into the modulation of alloy/metal oxide active interfaces, contributing to the development of efficient bifunctional catalysts for HER and HzOR.