Self-supported Electrocatalysts Research Articles

Designing Self-Supported Electrocatalysts for Electrochemical Water Splitting: Surface/Interface Engineering toward Enhanced Electrocatalytic Performance.

Electrochemical water splitting is regarded as the most attractive technique to store renewable electricity in the form of hydrogen fuel. However, the corresponding anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) remain challenging, which exhibit complex reactions and sluggish kinetic behaviors at the triple-phase interface. Material surface and interface engineering provide a feasible approach to improve catalytic activity. Besides, self-supported electrocatalysts have been proven to be highly efficient toward water splitting, because of the regulated catalyst/substrate interface. In this Review, the state-of-the-art achievements in self-supported electrocatalyst for HER/OER have demonstrated the feasibility of surface and interface engineering strategies to boost performance. The six key effective surface/interface engineering approaches for rational catalysts design are systematically reviewed, including defect engineering, morphology engineering, crystallographic tailoring, heterostructure design, catalyst/substrate interface engineering, and catalyst/electrolyte interface regulation. Finally, the challenges and opportunities on the valuable directions are proposed to inspire future investigation of highly active and durable HER/OER electrocatalysts.

Ultrafast Room-Temperature Synthesis of Self-Supported NiFe-Layered Double Hydroxide as Large-Current-Density Oxygen Evolution Electrocatalyst.

Water splitting is a promising sustainable technology to produce high purity hydrogen, but its commercial application remains a giant challenge due to the kinetically sluggish oxygen evolution reaction (OER). In this work, a time- and energy-saving approach to directly grow NiFe-layered double hydroxide (NiFe-LDH) nanosheets on nickel foam under ambient temperature and pressure is reported. These NiFe-LDH nanosheets are vertically rooted in nickel foam and interdigitated together to form a highly porous array, leading to numerous exposed active sites, reduced resistance of charge/mass transportation and enhanced mechanical stability. As self-supported electrocatalyst, the representative sample (NF@NiFe-LDH-1.5-4) shows an excellent large-current-density catalytic activity for OER in alkaline electrolyte, requiring low overpotentials of 190 and 220 mV to reach the current densities of 100 and 657 mA cm-2 with a Tafel slope of 38.1 mV dec-1 . In addition, NF@NiFe-LDH-1.5-4 as an overall water splitting electrocatalyst can stably achieve a large current density of 200 mA cm-2 over 300 h at a low cell voltage of 1.83 V, meeting the requirement of industrial hydrogen production. This exceedingly simple and ultrafast synthesis of low-cost and highly active large-current-density OER electrocatalysts can propel the commercialization of hydrogen producing technology via water splitting.

Nickel Boride/Boron Carbide Particles Embedded in Boron-Doped Phenolic Resin-Derived Carbon Coating on Nickel Foam for Oxygen Evolution Catalysis in Water and Seawater Splitting.

Electrolysis of seawater can be a promising technology, but chloride ions in seawater can lead to adverse side reactions and the corrosion of electrodes. A new transition metal boride-based self-supported electrocatalyst was prepared for efficient seawater electrolysis by directly soaking nickel foam (NF) in a mixture of phenolic resin (PR) and boron carbide (B4 C), followed by an 800 °C annealing. During PR carbonization process, the reaction of B4 C and NF generated nickel boride (Nix B) with high catalytic activity, while PR-derived carbon coating was doped with boron atoms from B4 C (B-CPR ). The B-CPR coating fixed Nix B/B4 C particles in the frames and holes to improve the space utilization of NF. Meanwhile, the B-CPR coating effectively protected the catalyst from the corrosion by seawater and facilitates the transport of electrons. The optimal Nix B/B4 C/B-CPR /NF required 1.50 and 1.58 V to deliver 100 and 500 mA cm-2 , respectively, in alkaline natural seawater for the oxygen evolution reaction.

Self‐Supported Electrocatalysts for Practical Water Electrolysis (Adv. Energy Mater. 39/2021)

Industrial Hydrogen Production In article number 2102074, Hongyuan Yang, Matthias Driess, and Prashanth W. Menezes comprehensively discuss the design and fabrication strategy for self-supported electrocatalysts with an aim of water electrolysis for industrial hydrogen production. The most promising electrocatalysts are further overviewed from the aspects of all-pH electrolyte capacity, seawater electrolysis, overall water splitting, large current density, and long-term durability along with a brief and concise perspective.

Methanol electroreforming coupled to green hydrogen production over bifunctional NiIr-based metal-organic framework nanosheet arrays

The conventional water electrolysis system is seriously restricted by the sluggish kinetics of anodic oxygen evolution reaction. Electroreforming of organic substances coupling with electrochemical hydrogen evolution is an innovative strategy to achieve energy-saving co-generation of value-added chemicals and hydrogen. Herein, NiIr-based metal‐organic framework (MOF) nanosheet arrays are in situ grown on Ni foam (NiIr-MOF/NF) and employed as a bifunctional self-supported electrocatalyst to oxidize small organic molecules of methanol to the value-added chemical formate while efficiently facilitating hydrogen production. The constructed co-electrolytic system based on HER-methanol oxidation reaction (MOR) bifunctional NiIr-MOF/NF electrocatalyst possesses ultra-high energy conversion efficiency for electrochemically assisted overall water splitting, with a low cell voltage of only 1.39 V to achieve the current density of 10 mA cm−2. Especially, the Faradaic efficiencies of the cathode and anode could both reach nearly 100% for H2 and formate generated in 1 M KOH containing 4 M methanol.

Constructing accelerated charge transfer channels along V-Co-Fe via introduction of V into CoFe-layered double hydroxides for overall water splitting

A series of self-supported electrocatalysts composed of tri-metallic CoFeV-LDHs generated on conductive carbon cloth (denoted as CoFeV@CC) have been constructed. The specific interaction among Co, Fe and V is systematically revealed via tuning the molar ratios of M2+:M3+ and Fe3+:V3+ in these tri-metallic LDHs. Finally, the optimal synergistic effect is reached when the molar ratios of M2+:M3+ and Fe3+:V3+ are respectively 4:1 and 1:1, resulting in the product named Co8FeV@CC, which displays the best overall OER and HER performance. Only rather low overpotentials of 235 and 182 mV are required to attain the current density of 100 mA cm−2 with a Faradaic efficiency of nearly 100 % for OER and HER, respectively. Co8FeV@CC can thus be applied as both an anode and cathode in the symmetrical two-electrode and possesses a current density of 100 mA cm−2 at the cell voltage of 1.65 V, and further demonstrates ultra-high stability for 100 h.

Interface engineering of porous Fe2P-WO2.92 catalyst with oxygen vacancies for highly active and stable large-current oxygen evolution and overall water splitting

Constructing a low cost, and high-efficiency oxygen evolution reaction (OER) electrocatalyst is of great significance for improving the performance of alkaline electrolyzer, which is still suffering from high-energy consumption. Herein, we created a porous iron phosphide and tungsten oxide self-supporting electrocatalyst with oxygen-containing vacancies on foam nickel (Fe2P-WO2.92/NF) through a facile in-situ growth, etching and phosphating strategies. The sequence-controllable strategy will not only generate oxygen vacancies and improve the charge transfer between Fe2P and WO2.92 components, but also improve the catalyst porosity and expose more active sites. Electrochemical studies illustrate that the Fe2P-WO2.92/NF catalyst presents good OER activity with a low overpotential of 267 mV at 100 mA cm−2, a small Tafel slope of 46.3 mV dec−1, high electrical conductivity, and reliable stability at high current density (100 mA cm−2 for over 60 h in 1.0 M KOH solution). Most significantly, the operating cell voltage of Fe2P-WO2.92/NF || Pt/C is as low as 1.90 V at 400 mA cm−2 in alkaline condition, which is one of the lowest reported in the literature. The electrocatalytic mechanism shows that the oxygen vacancies and the synergy between Fe2P and WO2.92 can adjust the electronic structure and provide more reaction sites, thereby synergistically increasing OER activity. This work provides a feasible strategy to fabricate high-efficiency and stable non-noble metal OER electrocatalysts on the engineering interface.

Synergistic engineering of morphology and electronic structure in constructing metal-organic framework-derived Ru doped cobalt-nickel oxide heterostructure towards efficient alkaline hydrogen evolution reaction

Hydrogen generation by alkaline electrochemical water splitting urgently requires new techniques capable of fabricating efficient and robust electrocatalysts for hydrogen evolution reaction (HER). However, it remains a major challenge to achieve this aim through a conjoint modulation in morphology and electronic structure. Herein, a metal–organic framework-derived (MOF-derived) Ru doped cobalt–nickel oxide heterostructure grown on Ni foam (Ru-Co3O4-NiO-NF) is fabricated by a simple and scalable preparation method. Systematic experimental characterizations verify that through a tailored low-temperature annealing process, the resulted Ru-Co3O4-NiO-NF can effectively inherit the advantageous two-dimensional (2D) nanosheet morphology of Co-MOF precursor and simultaneously maintain the mechanical robustness of three-dimensional (3D) Ni foam, which are beneficial for active site exposure and charge or mass transport. Furthermore, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation are hired to reveal that Ru-doping and Co3O4-NiO heterointerface can collectively regulate the electronic state of Ni and Co sites, thus optimizing the H2O adsorption/desorption and proton adsorption in alkaline HER process. As expected, the optimized Ru-Co3O4-NiO-NF is much more active than the commercial Pt-C (20 wt%) for electrocatalytic HER in 1 M KOH, exhibiting the low overpotential of 44 mV and 115 mV at the current density of 10 mA cm−2 and 100 mA cm−2. Moreover, the obtained self-supported electrode material can maintain catalytic activity over 60 h at 100 mA cm−2 without significant decay. This study provides a new perspective for constructing the advanced MOF-derived alkaline HER self-supported electrocatalysts by synergistic engineering of morphology and electronic structure for future energy application.

Cobalt-doped cerium oxide nanocrystals shelled 1D SnO2 structures for highly sensitive and selective xanthine detection in biofluids

In this study, we prepared a three-dimensional self-supported electrocatalyst based on a thin layer of cerium oxide nanocrystals doped with cobalt heteroatoms (CeO2-Co) and then uniformly shelled over one-dimensional tin oxide (SnO2) nanorods supported by carbon cloth substrate. The material was used as a binder-free sensor that could nonenzymatically detect xanthine (XA) with an excellent sensitivity of 3.56 μA μM−1, wide linear range of 25 nM to 55 µM, low detection limit of 58 nM, and good selectivity. A screen-printed electrode based on the material accurately detected XA in food samples as well. The achievements were resulted from synergistic effects coming from the unique core@shell formation and Co-doping strategy, which efficiently modified electronic structure of the material to expose more electroactive site numbers/types and fast charge transfer, thereby producing intrinsic catalytic properties for XA oxidation. These results suggested that the SnO2@CeO2-Co is potential for developing efficient sensor to detect XA with good sensitivity and accuracy in food-quality monitoring.

FeCoNiB@Boron-doped vertically aligned graphene arrays: A self-supported electrocatalyst for overall water splitting in a wide pH range

The development of efficient, cost-effective, bifunctional and self-supported electrocatalysts for overall water splitting in a wide pH range is highly desirable. A novel and highly efficient electrocatalyst for overall water splitting in a wide pH range was synthesized via the electroless plating of FeCoNiB alloy nanoparticles on B-doped vertically aligned graphene arrays (FeCoNiB@B-VG). FeCoNiB@B-VG exhibited excellent electrocatalytic performances with a low overpotential of 31 mV in 1.0 M KOH and 148 mV in 0.5 M H2SO4 for hydrogen evolution reaction (HER), and an overpotential of 387 mV in 1.0 M KOH for oxygen evolution reaction (OER). It also exhibited a quite low Tafel slope value of 30 mV dec−1 and 51 mV dec−1 for HER and OER in 1.0 M KOH respectively. In addition, FeCoNiB@B-VG also exhibited good long-term stabilities in acidic and alkaline electrolytes as a self-supported bifunctional electrocatalyst. This work may provide theoretical and technical support for design of cost-effective bifunctional electrocatalysts for overall water splitting in a wide pH range.

Co-doped NixPy loading on Co3O4 embedded in Ni foam as a hierarchically porous self-supported electrode for overall water splitting

It had remained a challenge to rationally design a highly efficient bifunctional catalyst for overall water splitting using non-precious metals. Herein, a simple method was presented to synthesize a self-supported catalyst using nickel foam (NF) filled with nanoscale Co3O4 (Co3O4/NF) as a hierarchical porous support. A NiCoP alloy was deposited on the Co3O4/NF in the form of profiling growth by electroless plating ([email protected]3O4/NF). And then, the [email protected]3O4/NF electrodes were phosphorylated. The profile-grown NiCoP alloy transformed into a two-dimensional (2D) flake-like Co-doped NixPy, forming a self-supported electrocatalyst (Co-NixPy@Co3O4/NF). The Co-NixPy@Co3O4/NF electrode exhibited a large surface area, excellent conductivity, and synergy between metal atoms. This electrode also possessed low overpotentials of 72 and 120 mV to drive the hydrogen and oxygen evolution reactions at 10 mA cm−2. For overall water splitting, the self-supported Co-NixPy@Co3O4/NF electrode only required a low voltage of 1.47 V to reach the current densities of 20 mA cm−2 in 1 M KOH with long-term stability for 36 h. This work represented an achievement the exploration of a new bifunctional of transition metal phosphides with high performances in water splitting.

Cu2Se nanowires shelled with NiFe layered double hydroxide nanosheets for overall water-splitting

It is imperative but challenging to develop non-noble metal-based bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Our work reports a core–shell nanostructure that is constructed by the electrodeposition of ultrathin NiFe-LDH nanosheets (NiFe-LDHNS) on Cu2Se nanowires, which are obtained by selenizing Cu(OH)2 nanowires in situ grown on Cu foam. The obtained Cu2Se@NiFe-LDHNS electrocatalyst provides more exposed edges and catalytic active sites, thus exhibiting excellent OER and HER electrocatalytic performance in alkaline electrolytes. This catalyst needs only an overpotential of 197 mV for OER at 50 mA cm−2 and 195 mV for HER at 10 mA cm−2. Besides, when employed as a bifunctional catalyst for overall water-splitting, it requires a cell voltage of 1.67 V to reach 10 mA cm−2 in alkaline media. Furthermore, the corresponding water electrolyzer demonstrates robust durability for at least 40 h. The excellent performance of Cu2Se@NiFe-LDHNS might be ascribed to the synergistic effect from the ultrathin NiFe-LDHNS, the Cu2Se nanowires anchored on the Cu foam, and the formed core–shell nanostructure, which offers large surface area, ample active sites, and sufficient channels for gas and electrolyte diffusion. This work provides an efficient strategy for the fabrication of self-supported electrocatalysts for efficient overall water-splitting.

A self-supporting electrode with in-situ partial transformation of Fe-MOF into amorphous NiFe-LDH for efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) have been extensively researched in recent years benefiting from the large surface area, abundant active centers, and adjustable structure. However, low conductivity and inaccessible active sites severely hinder its application in water electrolysis. Herein, a self-supporting electrocatalyst by developing MOF derivative on the surface of iron foam (IF) was synthesized through a self-templated partial transformation strategy. In addition, a series of catalysts with different morphologies were synthesized by adjusting the amount of Ni and the reaction time. Profiting from the unique hierarchical structure with large active area and abundant active sites, strong combination of highly active amorphous NiFe-LDH and Fe-MOF, and high conductivity and stability of the MOFs array in situ growth on IF, the resulting NiFe-LDH@Fe-MOF/IF-2 shows excellent oxygen evolution reaction (OER) activity in alkaline electrolyte with required overpotentials of 183, 237 and 257 mV to achieve current densities of 10, 100, and 200 mA cm−2, respectively, and long-term stability for at least 20 h. This work provides new insights for the design and development of self-supporting MOFs derived high performance electrocatalysts.

Boron and phosphorus co-doped NiVFe LDHs@NF as a highly efficient self-supporting electrocatalyst for the hydrogen evolution reaction

Developing highly efficient, inexpensive, and stable electrocatalysts for hydrogen evolution reaction (HER) is indispensable to building a sustainable and large-scale hydrogen conversion system. In this work, we designed a ternary NiVFe layered double hydroxide nanosheet on porous nickel foam via hydrothermal method to prepare a self-supporting electrocatalyst and co-doped with boron and phosphorus which control the electronic structure of the nanosheets. Simultaneous, the B-P co-doping formation numerous defects and amorphous regions on the nanosheet, which guarantees efficient active sites and enhanced active surface area. As expected, the electrochemical test of HER results shows that the NiVFe-B-P LDHs@NF requires an overpotentials of 112 mV at a current density of 10 mA·cm −2 in the 1.0 M KOH electrolyte without iR compensation, as well as exhibits excellent stability of 24 h at current densities of 10 mA·cm −2 and 50mA·cm −2 , respectively. Moreover, evaluation of wettability shows that the electrocatalyst has excellent superhydrophilicity and superaerophobicity. We expect the results of this work provides a fresh perspective for double-nonmetal co-doping electrocatalysts with efficient hydrogen generation. • NiVFe-B-P LDHs@NF exhibits the low overpotential of 117 mV at 10 mA·cm −2 for HER. • The synergistic effect of B-P co-doping results in superior HER performance. • The superhydrophilic electrode is prepared, which can accelerate the bubbles detachment. Developing highly efficient, inexpensive, and stable electrocatalysts for hydrogen evolution reaction (HER) is indispensable to building a sustainable and large-scale hydrogen conversion system. In this work, we designed a ternary NiVFe layered double hydroxide nanosheet on porous nickel foam via hydrothermal method to prepare a self-supporting electrocatalyst and co-doped with boron and phosphorus which control the electronic structure of the nanosheets. Simultaneous, the B-P co-doping formation numerous defects and amorphous regions on the nanosheet, which guarantees efficient active sites and enhanced active surface area. As expected, the electrochemical test of HER results shows that the NiVFe-B-P LDHs@NF requires an overpotentials of 117 mV at a current density of 10 mA·cm −2 in the 1.0 M KOH electrolyte without iR compensation, as well as exhibits excellent stability of 24 h at current densities of 10 mA·cm −2 and 50 mA·cm −2 , respectively. Moreover, evaluation of wettability shows that the electrocatalyst has excellent superhydrophilicity and superaerophobicity. We expect the results of this work provides a fresh perspective for double-nonmetal co-doping electrocatalysts with efficient hydrogen generation.

NiFeP nanosheets on N-doped carbon sponge as a hierarchically structured bifunctional electrocatalyst for efficient overall water splitting

The advancement of high-performance and low-cost bifunctional electrocatalysts, for the hydrogen and oxygen evolution reaction (HER and OER), is significant to realize the commercialization of electrocatalytic overall water splitting. Herein, two-dimensional (2D) holey NiFeP nanoarrays are vertically grown on a three-dimensional (3D) porous nitrogen-doped carbon sponge (N-CS) to form a hierarchically self-supported electrocatalyst (named NiFeP@N-CS) for efficient water splitting. Benefiting from the bimetal synergy effect and the hierarchical structure, the obtained bifunctional electrocatalyst NiFeP@N-CS exhibits high electrocatalytic performance for HER and OER (186 mV and 216 mV at 10 mA cm−2) in 1.0 M KOH. As a result, the water electrolyzer assembled by NiFeP@N-CS electrocatalyst as both anode and cathode only requires 1.63 V at the same current density and maintains outstanding durability up to 24 h. The present work extends the application of electrocatalysts with the hierarchical structure in the field of electrochemical overall water splitting.

In-situ transformational mycelium-like metal phosphides-encapsulated carbon nanotubes coating on the stainless steel mesh as robust self-supporting electrocatalyst for water splitting

Herein, In-situ conversional mycelium-like metal phosphides-encapsulated N, P co-doped carbon nanotubes (CNTs) coating on the stainless steel mesh (PSD-SM) as self-supporting electrocatalyst was fabricated via solid-diffusion (SD) and phosphorization process, which was the first time to fabricated the “chainmail for catalysts” use stainless steel mesh worked as self-reaction template and electrode-base materilas. The in-situ transformational mycelium-like CNTs array structure greatly enhanced the specific surface area of steel mesh and the graphitized carbon layer coating with high capacitance increases the electrochemical active sites. And the subsequent phosphorization treatment further improved the intrinsic catalytic activity of the material. PSD-SM exhibits the low overpotential of 231 mV at 10 mA·cm−2 with a Tafel slope of 88 mV·dec−1 for OER and 172 mV at 10 mA·cm−2 with a Tafel slope of 125 mV·dec−1 for HER. Further more, there are only 1.77 V deliver potential for water electrolysis of PSD-SM at 10 mA·cm−2 and the kinetic mechanism of as-fabricated samples for HER and OER was analyzed by Tafel slope and other measurement. This report provides an promising method to prepare efficient and robust electrocatalytic materials based on steel mesh for practical application.

Solar-driven hydrogen generation coupled with urea electrolysis by an oxygen vacancy-rich catalyst

Urea, an environmental pollutant for both soil and water, is widely present in wastewater. On the other hand, a strategy utilizing renewable electricity to decrease the cost of green hydrogen, which holds the key to a sustainable energy future, is promising but challenging. Gas crossover that generates explosive hydrogen–oxygen mixture becomes very serious with intermittent renewable power source (partial load issue). Herein, we address these issues in one device, i.e., a hybrid electrolyzer where water oxidation that produces oxygen is replaced by urea oxidation which generates inert gases. A self-supported electrocatalyst of nitrogen-doped nickel-iron oxyhydroxide derived from waste rusty iron foam is synthesized via an in situ ‘waste-to-value’ synthetic route followed by an ammonia/argon plasma treatment, which reconstructs the surface of the catalyst to a 3D nanosheet-like porous network with abundant oxygen vacancies. The as-prepared catalyst shows a small potential of 1.45 V vs. RHE at 500 mA cm−2 for urea oxidation. Overall water-urea electrolysis only requires 1.58 V to deliver 100 mA cm−2, which is 0.33 V less than that in urea-free water splitting, and thus lowers the overall energy consumption by 17.3%. Without oxygen evolution, the hybrid electrolysis does not suffer from the safety hazard caused by explosive hydrogen–oxygen mixture. We demonstrate the safe production of green hydrogen (3.1% oxygen in the gaseous product) in the hybrid electrolysis powered by solar energy via a photovoltaic panel. Our work provides a method to address the urea-caused environmental issues and simultaneously generate green hydrogen safely using solar energy.

Improving hydrogen evolution activity of two-dimensional nanosheets MoNi4/MoO2.5-NF self-supporting electrocatalyst by electrochemical-cycling activation

Improving hydrogen evolution activity of two-dimensional nanosheets MoNi4/MoO2.5-NF self-supporting electrocatalyst by electrochemical-cycling activation

The in situ growth of Cu2O with a honeycomb structure on a roughed graphite paper for the efficient electroreduction of CO2 to C2H4

A Cu2O/NGP self-supporting electrocatalyst is used for the electrocatalytic reduction of CO2 to ethylene to solve environmental and energy problems.

Cooperativity of Cu and Pd active sites in CuPd aerogels enhances nitrate electroreduction to ammonia.

By rationally choosing Pd as an active metal and Cu as a promoting metal, we developed Cu-rich CuPd bimetallic aerogels as a self-supported electrocatalyst for nitrate electroreduction. The spongy aerogel structure provides abundant catalytically active sites, while the synergistic benefit of the CuPd binary composition increases their reactivity, helping to achieve efficient nitrate-to-ammonia conversion.