Electronic regulation of platinum species on metal nitrides realizes superior mass activity for hydrogen production

Rational Design of Molybdenum-Doped Cobalt Nitride Nanowire Arrays for Robust Overall Water Splitting

Rational design of efficient electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct self-supported Co₃ N nanowire arrays with different Mo doping contents by hydrothermal and nitridation processes that serve as robust electrocatalysts for overall water splitting. The optimal Co₃ N-Mo_0.2 /Ni foam (NF) electrode delivers a low overpotential of 97 mV at a current density of 50 mA cm^-2 as well as a highly stable hydrogen evolution reaction (HER). Density functional theory (DFT) calculations prove that Mo doping can effectively modulate the electronic structure and surface adsorption energies of H₂ O and hydrogen intermediates on Co₃ N, leading to improved reaction kinetics with high catalytic activity. Further modification with FeOOH species on the surface of Co₃ N-Mo_0.2 /NF improves the oxygen evolution reaction (OER) performance benefiting from the synergistic effect of dual Co-Fe catalytic centers. As a result, the Co₃ N-Mo_0.2 @FeOOH/NF catalysts display outstanding OER catalytic performance with a low overpotential of 250 mV at 50 1 mA cm^-2 . The constructed Co₃ N-Mo_0.2 /NF||Co₃ N-Mo_0.2 @FeOOH/NF water electrolyzer exhibits a small voltage of 1.48 V to achieve a high current density of 50 mA cm^-2 at 80 °C, which is superior to most of the reported electrocatalysts. This work provides a new approach to developing robust electrode materials for electrocatalytic water splitting.

Engineering cobalt molybdate nanosheet arrays with phosphorus-modified nickel as heterogeneous electrodes for highly-active energy-saving water splitting

Electrochemical urea electrolysis has been regarded as a promising strategy to replace traditional water-splitting technology to achieve hydrogen fuel due to its cost savings and high energy efficiency. Designing efficient bifunctional electrocatalysts easily is important but still faces significant challenges. Herein, an interface engineering strategy is used to construct a hybrid material by coupling cobalt molybdate (CoMoO₄) nanosheet arrays with phosphorus-modified nickel (P-Ni) particles on copper foam (P-Ni@CoMoO₄/CF) through the hydrothermal and in-situ electrodeposition process. Benefiting from the abundant catalytic active sites, low charge transfer resistance, and synergistic coupling effect, the optimal P-Ni@CoMoO₄/CF electrocatalyst presents a superior bifunctional activity for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). In detail, a small overpotential of 125 mV and a low potential of 1.36 V is required to attain the current density of 100 mA cm^-2 for HER and UOR, respectively. In the process of urea electrolysis, the P-Ni@CoMoO₄/CF-based electrolyzer provides a current density of 100 mA cm^-2 with an overall voltage of 1.50 V, about 170 mV less than that in a traditional water electrolyzer. The high performance of P-Ni@CoMoO₄/CF outperforms many recently reported electrodes, suggesting its promising application in energy-saving hydrogen production. Our work proposes a novel idea for the rational design and exploitation of low-cost and robust bifunctional electrodes for electrocatalysis.

Carbon-encapsulated Co2P/P-modified NiMoO4 hierarchical heterojunction as superior pH-universal electrocatalyst for hydrogen production

The development of hydrogen evolution reaction (HER) technology that operates stably in a wide potential of hydrogen (pH) range of electrolytes is particular important for large-scale hydrogen production. However, the rational design of low-cost and pH-universal electrocatalyst with high catalytic performance remains a huge challenge. Herein, Co₂P nanoparticles strongly coupled with P-modified NiMoO₄ nanorods are directly grown on nickel foam (NF) substrates through carbon layer encapsulation (denoted as C-Co₂P@P-NiMoO₄/NF) by hydrothermal, deposition, and phosphating processes. This novel kind of hierarchical heterojunction has abundant heterogeneous interfaces, strong electronic interactions, and optimized reaction kinetics, representing the highly-active pH-universal electrodes for HER. Remarkably, the C-Co₂P@P-NiMoO₄/NF catalyst shows excellent HER properties in acidic and basic electrolytes, where the overpotentials of 105 mV and 107 mV are applied to drive the current density of 100 mA cm^-2. In addition, a low overpotential of 177 mV at 100 mA cm^-2 along with high stability is realized in 1 M phosphate buffer solution (PBS), which is close to the state-of-the-art non-precious metal electrocatalysts. Our work not only provides a class of robust pH-universal electrocatalyst but also offers a novel way for the rational design of other heterogeneous materials bythe interface regulation strategy.

Coupled MoO3-x@CoP heterostructure as a pH-universal electrode for hydrogen generation at a high current density

Developing high-performance and low-cost self-supporting electrodes as pH-universal electrocatalysts for the hydrogen-evolution reaction (HER) and realizing high-quality hydrogen production at a high current density are highly desirable, but are hugely challenging. We created a self-supporting electrode with a coupled hierarchical heterostructure by simple electrodeposition followed by sulfurization. It comprised oxygen-deficient molybdenum oxide (MoO_3-x) and cobalt phosphide (CoP) on nickel foam (NF), which represented a highly active pH-universal electrocatalyst for the HER at a high current density. Benefiting from a plethora of catalytic active sites, improved interfacial charge transfer, and strong electronic interaction, this type of MoO_3-x@CoP/NF electrode delivered a superior catalytic performance. Overpotentials of only 100 mV, 135 mV, and 400 mV were needed to realize a high current density of 1 A cm^-2 in alkaline, acid and neutral media, respectively, which were superior to those of most other well-developed materials based on non-noble metals. Our experimental work demonstrates the synergistic advantages of a MoO_3-x@CoP heterostructure for improving the intrinsic catalytic performance but also paves a new path for the rational design of advanced electrodes for hydrogen generation in a wide range of pH conditions.

Engineering Coupled NiSx -WO2.9 Heterostructure as pH-Universal Electrocatalyst for Hydrogen Evolution Reaction

Exploiting highly active and low-cost materials as pH-universal electrocatalysts for the hydrogen evolution reaction (HER) and achieving high-purity hydrogen fuel is highly desirable but remains challenging. Herein, a novel type of coupled heterostructure was designed by simple electrodeposition followed by a sulfurization treatment. This hierarchical structure was composed of nickel sulfides (NiS, NiS₂ , denoted as NiS_x ) and oxygen-deficient tungsten oxide (WO_2.9 ), which was directly grown on nickel foam (NF) as self-supporting electrodes (NiS_x -WO_2.9 /NF) for HER over a wide pH range. The systematic experimental characterizations confirmed that the material had abundant catalytic active sites, fast interfacial electron transfer ability, and strong electronic interaction, resulting in the optimized reaction kinetics for HER. Consequently, the NiS_x -WO_2.9 /NF catalyst required low overpotentials of 96 and 117 mV to reach current densities of 50 and 100 mA cm^-2 in an alkaline medium, outperforming most of the reported non-noble metal-based materials. Moreover, this self-supported electrode exhibited impressive performance over a wide pH range, only requiring 220 and 304 mV overpotential at 100 mA cm^-2 in 0.5 m H₂ SO₄ and 1 m phosphate-buffered saline electrolytes. This work may offer a new approach to the development of advanced pH-universal electrodes for hydrogen production.

Ni2 Se3 -CuSex Heterostructure as a Highly Efficient Bifunctional Electrocatalyst for Urea-Assisted Hydrogen Generation

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an attractive alternative anode reaction for electrochemical hydrogen generation with low energy consumption. However, the development of highly efficient bifunctional electrocatalysts is still a challenge. In this work, Ni₂ Se₃ -CuSe_x heterostructure was synthesized on copper foam (Ni₃ Se₂ @CuSe_x /CF) by electrodeposition accompanied by a selenization process. Benefiting from the abundant active sites, faster reaction kinetics, and modulated electronic structure, the self-supporting Ni₃ Se₂ @CuSe_x /CF electrode exhibited superior catalytic performance. Extremely low overpotentials of 120 and 140 mV were achieved at the current density of 100 mA cm^-2 for HER/UOR, respectively. Respectively, in HER||UOR coupled electrolyzer for H₂ generation, the Ni₃ Se₂ @CuSe_x /CF||Ni₃ Se₂ @CuSe_x /CF delivered a low cell voltage of 1.49 V to reach a high current density of 100 mA cm^-2 along with good stability, outperforming most of the other well-developed materials to date. The rational design of coupled heterostructure as bifunctional electrodes is a promising approach for energy-saving H₂ production.

A Three-Dimensional Melamine Sponge Modified with MnOx Mixed Graphitic Carbon Nitride for Photothermal Catalysis of Formaldehyde

Much attention has been paid to developing effective visible light catalytic technologies for VOC oxidation without requiring extra energy. In this paper, a series of sponge-based catalysts with rich three-dimensional porosity are synthesized by combining MnOx and graphitic carbon nitride (GCN) with commercial melamine sponges (MS) coated with polydopamine (PDA), demonstrating excellent photothermal catalytic performance for formaldehyde (HCHO). The three-dimensional porous framework of MS can provide a good surface for material modification and a reliable interface for gas-solid interaction. The grown layer of PDA framework not only increases the near-infrared wavelength absorption for improving the light-to-heat conversion of catalysts, but also brings excellent adhesion for the subsequent addition of MnO_X and GCN. The efficient formaldehyde oxidation is attributed to the sufficient oxygen vacancies generated by co-loaded MnO_X and GCN, which is conducive to the activation of more O²⁻ in the oxidation process. As the surface temperature of catalyst rapidly increases to its maximum value at ca. 115 °C under visible light irradiation, the HCHO concentration drops from 160 ppm to 46 ppm within 20 min. The reaction mechanism is certified as a classical Mars-van Krevelen mechanism based on the photo-induced thermal catalysis process.

Copper Incorporated Molybdenum Trioxide Nanosheet Realizing High-Efficient Performance for Hydrogen Production

The development of highly active non-precious metal electrocatalysts is crucial for advancing the practical application of hydrogen evolution reaction (HER). Doping engineering is one of the important strategies to optimize the electrocatalytic activity of electrocatalysts. Herein, we put forward a simple strategy to optimize the catalytic activity of MoO3 material by incorporating the Cu atoms into the interlayer (denoted as Cu-MoO3). The prepared Cu-MoO3 nanosheet has a larger surface area, higher conductivity, and strong electron interactions, which contributes to optimal reaction kinetics of the HER process. As a result, the Cu-MoO3 nanosheet only needs a small overpotential of 106 mV to reach the geometric current density of 10 mA cm−2. In addition, it also delivers a low Tafel slope of 83 mV dec−1, as well as high stability and Faraday efficiency. Notably, when using the Cu-MoO3 as a cathode to construct the water electrolyzer, it only needs 1.55 V to reach the 10 mA cm−2, indicating its promising application in hydrogen generation. This work provides a novel type of design strategy for a highly active electrocatalyst for an energy conversion system.

Heterostructure engineering of iridium species on nickel/molybdenum nitride for highly-efficient anion exchange membrane water electrolyzer

Developing highly active electrocatalysts is a pivotal issue for anion-exchange membrane water electrolyzers (AEMWE). However, realizing the continuous hydrogen generation at a large current density remains challenging. Herein, a novel kind of hybrid electrode is successfully developed by introducing trace iridium (Ir) species onto a hierarchical Ni/Mo₅N₆ heterostructure on Ni foam (Ir-Ni/Mo₅N₆/NF). The synergistic advantages of high conductivity, abundant active sites, and strong electronic interaction endow superior reaction kinetics, presenting a highly-active bifunctional electrocatalyst. Remarkably, the Ir-Ni/Mo₅N₆/NF exhibit extremely low overpotentials of 52 mV and 250 mV at 100 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). By exploiting the Ir-Ni/Mo₅N₆ as both anode/cathode, the constructed AEMWE device delivers superior performance. The current density reaches 2.1 A cm^-2 at a voltage of 2.0 V and 250 mA cm^-2 at 1.8 V in alkaline/neutral media. This work put forward a facile and effective strategy to synthesize advanced bifunctional electrocatalysts for water electrolysis.

Hierarchical Metal Sulfides Heterostructure as Superior Bifunctional Electrode for Overall Water Splitting

The development of highly active bifunctional electrocatalysts for overall water splitting is of significant importance, but huge challenges remain. The key element depends on engineering the electronic structure and surface properties of material to achieve improved catalytic activity. Herein, a hierarchical nanowire array of metal sulfides heterostructure on nickel foam (FeCoNiS_x /NF) was designed as a novel type of hybrid electrocatalyst for overall water splitting. The hybrid structure endowed plenty of catalytic active sites, strong electronic interactions, and high interfacial charge transferability, leading to superior bifunctional performance. As a result, the FeCoNiS_x /NF catalyst delivered low overpotentials of 97 and 260 mV at the current density of 50 mA cm^-2 for hydrogen and oxygen evolution reactions, respectively. Moreover, the FeCoNiS_x /NF-based water electrolyzer exhibited a small potential of 1.57 V for a high current density of 50 mA cm^-2 . These results indicate the promising application potential of FeCoNiS_x /NF electrode for hydrogen generation. This work provides a new approach to develop robust hybrid materials as the highly active electrode for electrocatalytic water splitting.

Fluorine-anion engineering endows superior bifunctional activity of nickel sulfide/phosphide heterostructure for overall water splitting

Designing advanced transition metal-based materials for electrocatalytic water splitting is of significance, but their wide application is still limited due to the lack of an effective regulation strategy. Herein, a synergistic regulation strategy of surface/interface is developed to optimize the catalytic activity of nickel sulfide (Ni₃S₂). The construction of nickel phosphide with Ni₃S₂ heterostructure by using fluorine (F)-anion modification is successfully developed on nickel foam (F-NiP_x/Ni₃S₂-NF) via a simple fluorination and phosphating treatment. This new kind of electrocatalyst contains plenty of active sites and strong electronic interactions, presenting superior bifunctional activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The overpotentials only need 182 mV and 370 mV to reach the current density of 100 mA cm^-2 for HER and OER, respectively. In addition, the F-NiP_x/Ni₃S₂-NF-based electrolyzer delivers promising performance for overall water splitting. A low potential of 1.55 V and 1.7 V can be achieved at the current density of 10 mA cm^-2 and 50 mA cm^-2. This work provides a new surface/interface regulation strategy for high-efficient bifunctional electrocatalysts.

Dual-anions engineering of bimetallic oxides as highly active electrocatalyst for boosted overall water splitting

Bimetallic oxides have unique advantages in driving both oxygen and hydrogen evolution reactions (OER/HER). Surface engineering of bimetallic oxides is a promising way to boost the catalytic activity by the regulation of electronic structure and surface property. Herein, a dual P, S-anions modification strategy is developed to optimize the catalytic performance of CoMoO₄ nanowire arrays. The formations of CoP and Co₃S₄ species on the CoMoO₄ surface bring heterojunction interfaces for more catalytic active sites and strong electronic interaction for faster interfacial charge transfer. Benefiting from these advantages, the P, S-CoMoO₄ catalyst on nickel foam (NF) delivers excellent catalytic activity and stability. The overpotentials at 10 mA cm^-2 of P, S-CoMoO₄/NF for HER are just 31 mV in acid media and 58 mV in alkaline media, respectively. In addition, by assembling the P, S-CoMoO₄/NF as bifunctional electrodes for overall water splitting, the electrolyzer exhibits a voltage of as low as 1.66 V at a current density of 50 mA cm^-2. This work put forward a new avenue for the development of advanced bifunctional electrocatalysts for water splitting.

Hierarchically structured nickel/molybdenum nitride heterojunctions as superior bifunctional electrodes for overall water splitting

A 3D hierarchical heterostructure of intermetallic compound heterojunctions is first rationally designed and presented as a highly-active bifunctional electrode for water splitting.