Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation

Two-Dimensional Zeolitic Imidazolate Framework-L-Derived Iron-Cobalt Oxide Nanoparticle-Composed Nanosheet Array for Water Oxidation

Rational design of various functional nanomaterials using MOFs as a template provides an effective strategy to synthesize electrocatalysts for water splitting. In this work, we reported that an iron-cobalt oxide with 2D well-aligned nanoflakes assembling on carbon cloth (Fe-Co₃O₄ NS/CC), fabricated by an anion-exchange reaction followed by an annealing process, could serve as a high-performance oxygen-evolving catalyst. Specifically, the zeolitic imidazolate framework-L-Co nanosheet array (ZIF-L-Co NS/CC) was synthesized through a facile ambient liquid-phase deposition reaction, and then reacted with [Fe(CN)₆]^3- ions as precursors during the anion-exchange reaction at room temperature. Finally, the Fe-Co₃O₄ NS/CC was obtained via annealing treatment. On account of the compositional and structural superiority, this 3D monolithic anode exhibited outstanding electrocatalytic performance with a low overpotential of 290 mV to obtain a geometrical current density of 10 mA cm^-2 and good durability for water oxidation in base.

Towards Solar Methanol: Past, Present, and Future

This work aims to provide an overview of producing value-added products affordably and sustainably from greenhouse gases (GHGs). Methanol (MeOH) is one such product, and is one of the most widely used chemicals, employed as a feedstock for ≈30% of industrial chemicals. The starting materials are analogous to those feeding natural processes: water, CO2, and light. Innovative technologies from this effort have global significance, as they allow GHG recycling, while providing society with a renewable carbon feedstock. Light, in the form of solar energy, assists the production process in some capacity. Various solar strategies of continually increasing technology readiness levels are compared to the commercial MeOH process, which uses a syngas feed derived from natural gas. These strategies include several key technologies, including solar-thermochemical, photochemical, and photovoltaic-electrochemical. Other solar-assisted technologies that are not yet commercial-ready are also discussed. The commercial-ready technologies are compared using a technoeconomic analysis, and the scalability of solar reactors is also discussed in the context of light-incorporating catalyst architectures and designs. Finally, how MeOH compares against other prospective products is briefly discussed, as well as the viability of the most promising solar MeOH strategy in an international context.

Cu3N nanowire array as a high-efficiency and durable electrocatalyst for oxygen evolution reaction

Developing non-precious oxygen evolution reaction (OER) electrocatalysts with high performance and long-term stability has drawn considerable research interest in recent years. In this communication, we report a self-supported Cu3N nanowire array on copper foam (Cu3N NA/CF) which is derived from a Cu(OH)2 nanowire array on copper foam (Cu(OH)2 NA/CF) through a nitridation process. Intriguingly, this 3D electrode exhibits marvellous OER activity with the need of an overpotential of only 298 mV at a current density of 20 mA cm-2 in 1.0 M KOH. In addition, the obtained electrocatalyst is capable of maintaining its high performance for at least 25 h under a static current density of 20 mA cm-2.

Porous Mn-Doped FeP/Co3 (PO4 )2 Nanosheets as Efficient Electrocatalysts for Overall Water Splitting in a Wide pH Range

Development of highly active and stable electrocatalysts for overall water splitting is important for future renewable energy systems. In this study, porous Mn-doped FeP/Co₃ (PO₄ )₂ (PMFCP) nanosheets on carbon cloth are utilized as a highly efficient 3 D self-supported binder-free integrated electrode for the oxygen evolution and hydrogen evolution reactions (OER and HER) over a wide pH range. Specifically, overpotentials of 27, 117, 85 mV are required for the PMFCP nanosheets to attain 10 mA cm^-2 for HER in 0.5 m H₂ SO₄ , 1.0 m phosphatebuffered saline (PBS), and 1.0 m KOH, respectively. In addition to the excellent performance for HER electrocatalysis, PMFCP nanosheets were also efficient electrocatalysts for the OER. Thus, the PMFCP nanosheets can serve as anodes and cathodes for overall water splitting (OWS). The OWS working voltages to attain 10 mA cm^-2 are found to be 1.75, 1.82, and 1.61 V in acid, neutral, and alkaline electrolytes, respectively. Chronopotentiometric tests show that the PMFCP electrode can maintain its excellent pH-universal OWS activity for more than 30 000 s. This work also provides new insights into developing high-performance electrocatalysts for water splitting over a wide pH range. The improvement in electrochemical performance by introduction of Mn dopant and nano-holes offers new opportunities in the development of effective electrodes for other energy-related applications.

Boosted Reactivity of Ammonia Borane Dehydrogenation over Ni/Ni2P Heterostructure

Ammonia borane (AB) is regarded as a highly promising candidate for chemical hydrogen-storage materials. Developing low-cost yet efficient catalysts for the dehydrogenation of AB is central to achieving hydrogen conversion. Here a heterostructure of Ni/Ni₂P nanoparticles deposited on a defective carbon framework for the hydrolysis of AB is developed by elaborately controlling phosphorization conditions. The electronic structure and interfacial interaction of the ternary components are probed by synchrotron-based X-ray absorption fine structure and further simulated via density functional theory. By adjusting the content of Ni and Ni₂P in the hetrostructure, the optimized hybrid exhibits catalytic performance of H₂ generation from the hydrolysis of AB under ambient conditions with a turnover frequency of 68.3 mol (H₂) mol^-1 (Cat) min^-1 and an activation energy ( E_a) of 44.99 kJ mol^-1, implying its high potential as an efficient supplement for noble-metal-based catalysts in hydrogen energy applications.

Cobalt-Tannin-Framework-Derived Amorphous Co-P/Co-N-C on N, P Co-Doped Porous Carbon with Abundant Active Moieties for Efficient Oxygen Reactions and Water Splitting

It remains a tremendous challenge to develop a low-cost, earth-abundant, and efficient catalyst with multifunctional activities for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Herein, a facile and scalable avenue was developed to prepare amorphous Co-P/Co-N-C supported on N, P co-doped porous carbon (Co-P/Co-N-C/NPC) with a large specific surface area (1462.9 m²  g^-1 ) and abundant reactive sites including Co-P, Co-N and NPC. The prepared electrocatalyst exhibits outstanding catalytic performance for HER (η=234 mV at 10 mA cm^-2 ), OER (η=374 mV at 10 mA cm^-2 ), and ORR (E_1/2 =0.89 V, vs. reversible hydrogen electrode). Benefiting from the excellent HER performance and outstanding OER activity, the Co-P/Co-N-C/NPC delivers a current density of 10 mA cm^-2 for overall water splitting at a cell voltage of 1.59 V, which is comparable with the IrO₂ -Pt/C couple electrode.

Ni nanoparticles supported on graphitic carbon nitride as visible light catalysts for hydrolytic dehydrogenation of ammonia borane

The development of a robust and low-cost non-noble metal catalyst for photocatalytic H2 evolution is of great importance for practical applications. In this study, monodisperse Ni nanoparticles of controlled sizes were prepared by a facile method and anchored on graphitic carbon nitride (g-C3N4) nanosheets via a self-assembly route. The noble-metal-free Ni/g-C3N4 composite catalysts exhibit excellent photocatalytic activities for the hydrolytic dehydrogenation of ammonia borane (AB) under visible light. An optimum AB hydrolysis rate was obtained when the size of the Ni NPs was 3.2 nm, with an initial turnover frequency of 18.7 mol(hydrogen) mol(catalyst)-1 min-1 and an apparent activation energy of 36 kJ mol-1. This study provides validity for constructing high performance first-row transition metal nano-photocatalysts for the hydrolytic dehydrogenation of AB.

Palladium/Bismuth/Copper Hierarchical Nano-Architectures for Efficient Hydrogen Evolution and Stable Hydrogen Detection

Efficient, stable electrode catalysts and advanced hydrogen sensing materials are the core of the hydrogen production and hydrogen detection for guaranteeing the safe issues. Although a universal material to achieve the above missions is highly desirable, it remains challenging. Here, we report palladium/bismuth/copper hierarchical nanoarchitectures (Pd/Bi/Cu HNAs) for advanced dual-applications toward hydrogen evolution reaction (HER) and hydrogen detection, via first electrodeposition of cylindrical nanowires and subsequent wet-chemical etching art. For HER, the Pd/Bi/Cu HNAs present the overpotential (79 mV at 10 mA^-2) and tafel slope (61 mV dec^-1) closing to those of Pt/C. For hydrogen detection, the Pd/Bi/Cu HNAs was able to work at a wide-temperature range (∼156-418 K), and remarkably, their critical temperature (∼156 K) of the "reversing sensing behavior" is much lower than that of pure Pd nanowires (278 K). These excellent performances are ascribed to the synergic effect of hierarchical morphology induced more exposure of Pd, and the Pd d-band modification via Cu and Bi dopants. It is feasible that Pd/Bi/Cu HNAs serve as universal materials for both efficient catalysts toward hydrogen evolution via water electrolysis and wide-temperature adapted hydrogen detection.

In pursuit of advanced materials from single-source precursors based on metal carbonyls

In this perspective, the development of single-source precursors and their relative advantages over multiple source approaches for the synthesis of metal pnictide solid state materials is explored. Particular efforts in the selective production of iron phosphide materials for catalytic applications are discussed, especially directed towards the hydrogen evolution and oxygen evolution reactions of water splitting.

Exceptional Performance of Hierarchical Ni-Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting

Developing low-cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth-abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni-Fe layered-double-hydroxide (Ni-Fe LDH) nanosheets or porous Ni-Fe oxides (NiFeO_x ) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as-prepared Ni-Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm^-2 at an overpotential of 218 mV, which is smaller than that of RuO₂ catalyst (249 mV). In contrast, the resulting NiFeO_x @NiCu exhibits better HER activity, yielding a current density of 10 mA cm^-2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide-based electrocatalysts. The remarkable activity of the Ni-Fe LDH@NiCu and NiFeO_x @NiCu is further demonstrated by a 1.5 V solar-panel-powered electrolyzer, resulting in current densities of 10 and 50 mA cm^-2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as-prepared materials as the best bifunctional electrocatalysts so far.

Highly crystalline Ni-doped FeP/carbon hollow nanorods as all-pH efficient and durable hydrogen evolving electrocatalysts

Herein, we report the synthesis of uniform hollow nanorods of Ni-doped FeP nanocrystals hybridized with carbon as electrocataysts for the electrocatalytic hydrogen evolution reaction (HER). These hollow nanorods are prepared based on the etching and coordination reaction between metal-organic frameworks and phytic acid, followed by a pyrolysis process. Benefiting from the abundant active sites, the improved mass and charge transport capability, the optimized Ni-doped FeP/C hollow nanorods exhibit excellent HER activities for achieving a current density of 10 mA cm^-2 at an overpotential of 72, 117, and 95 mV in acidic, neutral, and alkaline media, respectively, as well as superior stability. X-ray photoelectron spectroscopy and basic density functional theory calculations suggest that the improved HER activity originates from the synergistic modulation of the active components, structural and electronic properties. This protocol provides a general and friendly strategy to construct hollow phosphides for energy-related applications.

Enhancement of alkaline water splitting activity by Co-P coating on a copper oxide nanowire

Hydrogen is the most attractive source of energy in the 21st century. However, high-efficiency mass production of hydrogen still faces many challenges. Although electrochemical water splitting is an ideal way to produce hydrogen, it requires low-cost and efficient electrocatalysts. In this work, a hybrid shell/core Co-P/CuO nanowire array was fabricated by Co-P film electrodeposition on a CuO nanowire array. Because of the synergy between Co-P and CuO nanowire arrays, Co-P/CuO shows remarkable activity toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). This bifunctional electrocatalyst achieving 20 mA cm-2 requires a cell voltage of only 1.645 V, and has superb long-term electrochemical stability and high faradaic efficiency.

Graphdiyne-Supported NiFe Layered Double Hydroxide Nanosheets as Functional Electrocatalysts for Oxygen Evolution

Graphdiyne (GDY), a novel two-dimensional full-carbon material, has attracted lots of attention because of its high conjugated system comprising sp² and sp-hybridized carbons. The distinctive structure characteristics endow it unique electronic structure, uniform distributed pores and excellent chemical stability. A novel GDY-supported NiFe layered double hydroxide (LDH) composite was successfully prepared for the first time. By taking advantage of the increased surface active areas and improved conductivity, the designed hierarchical GDY@NiFe composite exhibits outstanding catalytic activity that only required a small overpotential about 260 mV to achieve the current density of 10 mA cm^-2. The nanocomposite shows excellent durability in alkaline medium implying a superior OER electrocatalytic activity. It is anticipated that the as-prepared GDY@NiFe composite electrocatalyst provide new insights in designing graphdiyne-supported electrocatalyst materials for oxygen evolution application.

Ultrathin Graphdiyne-Wrapped Iron Carbonate Hydroxide Nanosheets toward Efficient Water Splitting

We employed a two-step strategy for preparing ultrathin graphdiyne-wrapped iron carbonate hydroxide nanosheets on nickel foam (FeCH@GDY/NF) as the efficient catalysts toward the electrical splitting water. The introduction of naturally porous GDY nanolayers on FeCH surface endows the pristine catalyst with structural advantages for boosting catalytic performances. Benefited from the protection of robust GDY nanolayers with intimate contact between GDY and FeCH, the combined material exhibits high long-term durability of 10 000 cycles for oxygen-evolution reaction (OER) and 9000 cycles for hydrogen evolution reaction (HER) in 1.0 M KOH. Such excellent bifunctional OER/HER performance makes FeCH@GDY/NF quite qualified for alkaline two-electrode electrolyzer. Remarkably, such electrocatalyst can drive 10 and 100 mA cm^-2 at 1.49 and 1.53 V, respectively. These results demonstrate the decisive role of GDY in the improvement of electrocatalytic performances, and open up new opportunities for designing cost-effective, efficient, and stable electrocatalysts for sustainable oxygen/hydrogen generation.

Cu-Co-M arrays on Ni foam as monolithic structured catalysts for water splitting: effects of co-doped S-P

Finding new methods to design environmentally friendly, highly stable, and robust oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts remains an extremely important challenge and affords several opportunities for exploiting the water-splitting process. In our work, Cu-Co-M (M = O, S, P, Se, S-P, and P-S) materials were grown in situ on three-dimensional (3D) porous nickel foam (NF) with good electrical conductivity by hydrothermal synthesis, vulcanization, selenylation, and phosphorization of the Cu-Co-precursor under an Ar atmosphere. Cu-Co-P-S/NF presents an overpotential value of 220 mV at 50 mA cm-2 for OER and that for Cu-Co-P-S/NF of 120 mV at 10 mA cm-2 for HER in an alkaline medium. In addition, considering the superior activities of Cu-Co-P-S/NF for OER and HER, the electrode pairing of Cu-Co-P-SOER//Cu-Co-P-SHER is designed for overall water splitting, and the experimental result shows that only a cell voltage of 1.55 V is needed to obtain a current density of 20 mA cm-2. According to the literature, this cell voltage is also among the lowest values that have been previously reported for electrocatalytic water splitting. Further, Cu-Co-P-S//Cu-Co-P-S exhibited efficient stability during a 20 h durability test without significant attenuation under alkaline conditions. By using XPS spectroscopy characterization, it was shown that Cu-Co-P-S presented the highest catalytic performance and long-term durability owing to the abundance of Co3+. The novelty of selecting the highest activity with the same catalyst for OER and HER from Cu-Co-M (M = O, S, P, Se, S-P, and P-S) in order to obtain a well-matched electrode pair, and therefore, simplifying the water-splitting device affords a wide range of possibilities for further exploitation of environmentally friendly and highly efficient electrode pairs.

Atomically thick Ni(OH)2 nanomeshes for urea electrooxidation

Atomically thick ultrathin nanomeshes (NMs) possessing the inherent advantages of both two-dimensional nanomaterials and porous nanomaterials are attracting increasing interest in catalysis and electrocatalysis. Herein, we report a direct chemical synthesis of atomically thick Ni(OH)2-NMs by a NaBH4 assisted cyanogel hydrolysis method, which overcomes the shortcoming of the post-etching method for NM synthesis. Various physical characterization methods show that the as-synthesized Ni(OH)2-NMs have 1.7 nm thickness, a big surface area, abundant nanoholes, and numerous surface/edge atoms with low-coordination numbers. The as-synthesized Ni(OH)2-NMs show a better electrocatalytic performance for the urea oxidation reaction than conventional Ni(OH)2 nanoparticles without holes in the alkaline electrolyte, including a lower onset oxidation potential, faster reaction kinetics, and higher mass activity.

Multishelled FeCo@FeCoP@C Hollow Spheres as Highly Efficient Hydrogen Evolution Catalysts

Active nonprecious metal-based hydrogen evolution reaction (HER) electrocatalysts are critical for the clean and sustainable generation of hydrogen. Here, we synthesized multishelled FeCo@FeCoP@C hollow spheres by the carbonization and phosphorization of the FeCo-MIL-88 metal-organic framework. Owing to both composition (FeCo mixed phosphide) and morphology (multishelled morphology) effects, the as-obtained FeCo@FeCoP@C exhibits excellent HER performance with a low overpotential of 65 mV to achieve an HER current density of 10 mA cm^-2 and high stability in acidic solution. Density functional theory calculations show that the FeCoP have the optimal hydrogen absorption energy than that of FeP and CoP. The carbon shell prevents the oxidation of the phosphides, and the FeCo core provides better conductivity. Our work provides a new method to synthesize multishelled structure catalysts, which has potential applications in the further hydrogen production.

Three-dimensional flower-like Ni–Mn–S on Ti mesh: a monolithic electrochemical platform for detecting glucose

Three-dimensional flower-like Ni–Mn–S on Ti mesh as a monolithic electrochemical platform was constructed and exhibited satisfactory glucose sensing performance.

Enhanced electrocatalytic activity of water oxidation in an alkaline medium via Fe doping in CoS2 nanosheets

Fe–CoS₂/CC exhibits enhanced catalytic OER performance, needing an overpotential of 302 mV at 10 mA cm⁻² in 1.0 M KOH.

Strongly Coupled Nickel-Cobalt Nitrides/Carbon Hybrid Nanocages with Pt-Like Activity for Hydrogen Evolution Catalysis

Designing non-precious-metal catalysts with comparable mass activity to state-of-the-art noble-metal catalysts for the hydrogen evolution reaction (HER) in alkaline solution still remains a significant challenge. Herein a new strongly coupled nickel-cobalt nitrides/carbon complex nanocage (NiCoNzocage) is rationally designed via chemical etching of ZIF-67 nanocubes with Ni(NO₃ )₂ under sonication at room temperature, following nitridation. The as-prepared strongly coupled NiCoN/C nanocages exhibit a mass activity of 0.204 mA µg^-1 at an overpotential of 200 mV for the HER in alkaline solution, which is comparable to that of commercial Pt/C (0.451 mA µg^-1 ). The strongly coupled NiCoN/C nanocages also possess superior stability for the HER with negligible current loss under the overpotentials of 200 mV for 10 h. Density functional theory (DFT) calculations reveal that the excellent HER performance under alkaline condition arises from the robust Co²⁺ →Co⁰ transformation achieved by strong (Ni, Co)N-bonding-induced efficient d-p-d coupled electron transfer, which is a key for optimal initial water adsorption and splitting. The high degree of amorphization urges the C-sites to be an electron-pushing bath to promote the inter-layer/sites electron-transfer with loss of the orbital-selection-forbidden-rule, which uniformly boosts the surface catalytic activities up to a high level independent of the individual surface active sites.

Ambient electrochemical N2-to-NH3 fixation enabled by Nb2O5 nanowire array

A Nb₂O₅ nanowire array on carbon cloth (Nb₂O₅/CC) is efficient for ambient electrocatalytic N₂-to-NH₃ fixation with excellent selectivity in 0.1 M Na₂SO₄.

Concentrated-acid triggered superfast generation of porous amorphous cobalt oxide toward efficient water oxidation catalysis in alkaline solution

Amorphous cobalt oxide on carbon cloth (AMO-CoO/CC) was prepared as an excellent water-oxidation catalyst with 50 mV less overpotential at 10 mA cm⁻² than highly-crystallized Co₃O₄ in 1.0 M KOH.

Oxygen vacancy-confined CoMoO4@CoNiO2 nanorod arrays for oxygen evolution with improved performance

Experimental and DFT calculation results show that the presence of oxygen vacancies can decrease the adsorption energy of intermediates at active sites and facilitate the adsorption of intermediates, thus improving the catalytic properties.

In situ growth of Fe(ii)-MOF-74 nanoarrays on nickel foam as an efficient electrocatalytic electrode for water oxidation: a mechanistic study on valence engineering

DFT results first demonstrate that varying the metal valence can tune the stable intrinsic electronic structure of MOF, different valence Fe(ii) and Fe(iii)-MOF-74 nanoarrrays on nickel foam are further synthesized as electrode for water oxidation.

Toward Bifunctional Overall Water Splitting Electrocatalyst: General Preparation of Transition Metal Phosphide Nanoparticles Decorated N-Doped Porous Carbon Spheres

It is very important to explore novel synthesis strategies for constructing highly active and inexpensive electrocatalysts for water-splitting. In present work, a novel and efficient coordination-polymerization-pyrolysis (CPP) strategy was developed to prepare cobalt phosphide nanoparticles modified N-doped porous carbon spheres (CoP@NPCSs) hybrids as a powerful catalyst for overall water-splitting (OWS). It can be found that both the carbonization temperatures and the metal contents affect the electrocatalytic performances. As a result, a device assembled with CoP@NPCSs demonstrates low potential (1.643 V @ 10 mA·cm^-2) and good stabilization for OWS. Besides, other transition metal phosphides (TMPs)-based materials also can be synthesized by the CPP approach, evidencing the generality of the CPP strategy. Here, we not only constructs a high-efficiency OWS catalyst, but also broadens the synthetic methodology of TMPs from nanoscale.

Structurally Engineered Hyperbranched NiCoP Arrays with Superior Electrocatalytic Activities toward Highly Efficient Overall Water Splitting

Developing inexpensive transition-metal-based nanomaterials with high electrocatalytic activity is of significant necessity for electrochemical water splitting. In this study, we propose a controllable structural engineering strategy of constructing a hyperbranched architecture for highly efficient hydrogen evolution reaction/oxygen evolution reaction (HER/OER). Hyperbranched NiCoP architecture organized by hierarchical nanorod-on-nanosheet arrays is rationally prepared as a demonstration via a facile solvothermal and phosphorization approach. A strong synergistic benefit from the multiscale building blocks is achieved to enable outstanding electrocatalytic properties in an alkaline electrolyzer, including low HER and OER overpotentials of 71 and 268 mV at 10 mA cm^-2, respectively, which significantly outperforms the counterparts of individual nanorods and nanosheets. The bifunctional catalysts also show highly efficient and durable overall water electrocatalysis with a small voltage of 1.57 V to drive a current density of 10 mA cm^-2. The present study will open a new window to engineering hyperbranched architectures with exceptional electrocatalytic activities toward overall water splitting.

Recent progress in transition metal phosphides with enhanced electrocatalysis for hydrogen evolution

Increasing demand for hydrogen energy has boosted the exploration of inexpensive and effective catalysts. Transition metal phosphides (TMPs) have been proven as excellent catalysts for the hydrogen evolution reaction (HER). Very recently, the search for TMP-based catalysts has being mainly directed at enhanced electrocatalytic performance. Hence, a concluded guideline for enhancing HER activity is highly desired. In this mini review, we briefly summarize the most recent and instructive developments in the design of TMP-based catalysts with enhanced electrocatalysis for hydrogen evolution from composition and structure engineering strategies. These strategies and perspectives are also meaningful for designing other inexpensive and high-performance catalysts.

Novel Cobalt-Doped Ni0.85Se Chalcogenides (Co xNi0.85- xSe) as High Active and Stable Electrocatalysts for Hydrogen Evolution Reaction in Electrolysis Water Splitting

In this paper, novel cobalt-doped Ni_0.85Se chalcogenides (Co _xNi_{0.85- x}Se, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co_0.1Ni_0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co_0.1Ni_0.75Se/rGO shows even better performance than unsupported Co_0.1Ni_0.75Se, which are confirmed by the reduction of HER overpotential of Co_0.1Ni_0.75Se/rGO to 103 mV compared to 153 mV of Co_0.1Ni_0.75Se at a current density of 10 mA/cm², and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co_0.1Ni_0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co_0.1Ni_0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.

Cobalt-Iron Oxide Nanoarrays Supported on Carbon Fiber Paper with High Stability for Electrochemical Oxygen Evolution at Large Current Densities

Here, we demonstrate that nonprecious CoFe-based oxide nanoarrays exhibit excellent electrocatalytic activity and superior stability for electrochemical oxygen evolution reaction (OER) at large current densities (>500 mA cm^-2). Carbon fiber paper (CFP) with three-dimensional macroporous structure, excellent corrosion resistance, and high electrical properties is used as the support material to prevent surface passivation during the long-term process of OER. Through a facile method of hydrothermal synthesis and thermal treatment, vertically aligned arrays of spinel Co _xFe_{3- x}O₄ nanostructures are homogeneously grown on CFP. The morphology and the Fe-doping content of the CoFe oxide nanoarrays can be controlled by the Fe³⁺ concentration in the precursor solution. The arrays of CoFe oxide nanosheets (NSs) grown on CFP (Co_2.3Fe_0.7O₄-NSs/CFP) deliver lower Tafel slope (34.3 mV dec^-1) than CoFe oxide nanowire (NW) arrays grown on CFP (Co_2.7Fe_0.3O₄-NWs/CFP) in alkaline solution, owing to higher Fe-doping content and larger effective specific surface area. The Co_2.3Fe_0.7O₄-NSs/CFP electrode exhibits excellent stability for OER at large current densities in alkaline solution. Moreover, the morphology and structure of CoFeO nanoarrays are well preserved after long-term testing, indicating the high stability for OER.

Bimetal Prussian Blue as a Continuously Variable Platform for Investigating the Composition-Activity Relationship of Phosphides-Based Electrocatalysts for Water Oxidation

Doping unary transition-metal phosphides (TMPs) by secondary metal is a powerful method to improve their catalytic activity for electrochemical oxygen evolution reaction (OER). However, the composition-activity relationship of such doping has not been systematically investigated yet because of the challenge in constructing bimetal TMPs with continuously variable composition while keeping homogenous elemental distribution. Herein, we develop a strategy of using bimetal Prussian blue analogues with homogenous elemental distribution at molecular scale as an ideal platform to achieve bimetal cobalt-iron phosphides (Co_{1- x}Fe _xP) with a continuously changeable Co/Fe ratio (0 < x < 1) and uniform metal distribution. Such a system allows us to draw out a composition-activity volcano profile of Co_{1- x}Fe _xP for OER. By optimizing the composition, the best catalytic activity is obtained at the Co/Fe ratio of 1.63 in Co_{1- x}Fe _xP with small overpotentials of 230 and 268 mV at 10 and 100 mA cm^-2, respectively, which outperform most of the reported TMPs. These results may inspire the use of multicomponent molecular platforms to understand composition-dependent performance and explore highly efficient catalysts for diverse applications.

Towards High-Efficiency Hydrogen Production through in situ Formation of Well-Dispersed Rhodium Nanoclusters

Rh-based materials have emerged as potential candidates for hydrogen revolution from electrolyzing water or ammonia borane (AB) hydrolysis. Nevertheless, most of the catalysts still suffer from the complex synthetic procedures combined with limited catalytic activity. Additionally, the facile syntheses of Rh catalysts with high efficiencies for both electrochemical water splitting and AB hydrolysis are still challenging. Herein, we develop a simple, green, and mass-producible ion-adsorption strategy to produce a Rh/C pre-catalyst (pre-Rh/C). The ultrafine and clean Rh nanoclusters immobilized on carbon are achieved via the in situ reduction of the pre-Rh/C during the hydrogen-evolution process. The resulting in situ Rh/C catalyst presents an outstanding electrocatalytic performance with low overpotentials of 8 and 30 mV at 10 mA cm^-2 in 1.0 m KOH and 0.5 m H₂ SO₄ , respectively, outperforming the state-of-the-art Pt catalysts. Furthermore, the in situ Rh/C is also highly active for AB hydrolysis to produce hydrogen with a high turnover frequency of 1246 mol H2  mol_Rh^-1  min^-1 at 25 °C. The in situ-formed ultrafine Rh nanoclusters are responsible for the observed superior catalytic performance. This facile in situ strategy to realize a highly active catalyst shows promise for practical applications.