In-situ cobalt and nitrogen doped mesoporous graphitic carbon electrocatalyst via directly pyrolyzing hyperbranched cobalt phthalocyanine for hydrogen evolution reaction

Catalytic Reinforcement in Hybrid Imidazole Functionalized Cobalt Phthalocyanine and Ketjenblack for Boosted Hydrogen Evolution

Hydrogen energy is widely regarded as one of the cleanest forms of green energy due to its bio-friendly nature. However, its commercialization is restricted by many issues. One of the major issues is related to high production cost, which can be overcome by designing of effective catalysts through simple, innovative and cost-effective approach for efficient green hydrogen production. In this study, we report the synthesis of an eco-friendly, affordable, and highly redox-active tetra-imidazole functionalized cobalt phthalocyanine (TImCoPc) through a straightforward method. To ensure its purity and effectiveness as an electrocatalyst for the hydrogen evolution reaction (HER) in 0.5 M H₂SO₄, various analytical techniques are employed for its thorough characterization. The electrocatalytic performance and conductivity of TImCoPc is further enhanced by forming hybrid with highly conductive Ketjenblack (KB) in various ratios. Among the different ratios, the 3.5 : 1.5 (TImCoPc/KB) composite exhibited excellent HER performance, with an onset potential closer to that of Pt/C and an overpotential (η₁₀) of -108 mV, closely approaching the η₁₀ of Pt/C (-36 mV). Additionally, the optimized hybrid showed a lower Tafel slope of 44 mV/dec, higher turnover frequency of 3.66x10-10 mol s-1 cm-2 and mass activity of 4.121 A mg-1, with an excellent catalytic stability, thereby proving to be one of the superior electrocatalysts for HER in terms of cost, methodology, activity and efficiency. The observed enhancement in HER activity of the hybrid can be accounted to the synergistic effects that reduce the metal ion's d-band center and improve π-π interactions between the hybrid components. The composite also demonstrated an increased electrochemical active surface area. This work highlights the potential of the TImCoPc/KB (3.5 : 1.5) composite as a cost-effective and efficient catalyst for sustainable hydrogen production.

Hydrogenation of Covalent Organic Framework Induces Conjugated π Bonds and Electronic Topological Transition to Enhance Hydrogen Evolution Catalysis

Recently, many topological materials have been discovered as promising electrocatalysts in chemical conversion processes and energy storage. However, it remains unclear how the topological electronic states specifically modulate the catalytic reaction. Here, the two-dimensional metal phthalocyanine-based covalent organic framework (MPc-COF) is studied by ab initio thermodynamic calculations to clearly reveal the promotional effect on the electrochemical hydrogen evolution reaction (HER) induced by topological gapless bands (TGBs). We find that the prehydrogenated (and fluorinated) H4CdPc-COF(F) shows the best HER performance, with 0.016 V (near zero) overpotential. By tracking changes to the electronic structure and free energy as the prehydrogenation and HER processes occur, we are able to separately attribute the high HER efficiency in part due to the increase of the electron bath by donating electrons to the conjugated π bonds and also to the existence of TGBs. Specifically, the significant catalytic promotion by TGBs is proven to decrease the free energy by 0.218 eV to near zero. When the TGBs are destroyed, e.g., by replacing N with P and opening a band gap, the HER efficiency is reduced. This study opens avenues for deterministically harnessing topological band features to improve electrocatalysis.

Selenium-transition metal supported on a mixture of reduced graphene oxide and silica template for water splitting

Exploration of economical, highly efficient, and environment friendly non-noble-metal-based electrocatalysts is necessary for hydrogen and oxygen evolution reactions (HER and OER) but challenging for cost-effective water splitting. Herein, metal selenium nanoparticles (M = Ni, Co & Fe) are anchored on the surface of reduced graphene oxide and a silica template (rGO-ST) through a simple one-pot solvothermal method. The resulting electrocatalyst composite can enhance mass/charge transfer and promote interaction between water molecules and electrocatalyst reactive sites. NiSe2/rGO-ST shows a remarkable overpotential (52.5 mV) at 10 mA cm-2 for the HER compared to the benchmark Pt/C E-TEK (29 mV), while the overpotential values of CoSeO3/rGO-ST and FeSe2/rGO-ST are 246 and 347 mV, respectively. The FeSe2/rGO-ST/NF shows a low overpotential (297 mV) at 50 mA cm-2 for the OER compared to RuO2/NF (325 mV), while the overpotentials of CoSeO3-rGO-ST/NF and NiSe2-rGO-ST/NF are 400 and 475 mV, respectively. Furthermore, all catalysts indicate negligible deterioration, indicating better stability during the process of HER and OER after a stability test of 60 h. The water splitting system composed of NiSe2-rGO-ST/NF||FeSe2-rGO-ST/NF electrodes requires only ∼1.75 V at 10 mA cm-2. Its performance is nearly close to that of a noble metal-based Pt/C/NF||RuO2/NF water splitting system.

Construction of core-shell Fe3O4@GO-CoPc photo-Fenton catalyst for superior removal of tetracycline: The role of GO in promotion of H2O2 to •OH conversion

A novel core-shell structured Fe₃O₄@GO-CoPc magnetic catalyst, which is with magnetite (Fe₃O₄) as the core, graphene oxide (GO) as the interlayer and cobalt-phthalocyanine (CoPc) as the shell, was successfully prepared and used as a heterogeneous photo-Fenton catalyst for tetracycline (TC) degradation in this work. The core-shell structure of the catalyst was confirmed by XRD, FTIR, SEM and TEM. BET and magnetic hysteresis loops measurements indicated that Fe₃O₄@GO-CoPc catalyst owned large specific surface area and could be easily recovered under an external magnetic field. Meanwhile, the experimental results of TC degradation demonstrated that the photo-Fenton efficiency of Fe₃O₄@GO-CoPc was excellent. When the reaction time was 120 min, TC could be degraded almost completely in the photo-Fenton system with Fe₃O₄@GO-CoPc. The high photo-Fenton catalytic activity of Fe₃O₄@GO-CoPc could be resulted from the effective transfer of photo-generated electrons between CoPc and Fe₃O₄ by GO. Moreover, the main reaction species, •OH, O₂•-, ¹O₂ and h⁺, were verified by the analysis of active species in this system. Finally, the mechanism analyses and quantitative analysis results of active species indicated that the introduction of GO accelerated the cycle between Fe(II) and Fe(III) as well as improved the effective utilization of H₂O₂ (the efficiency of conversion of H₂O₂ to •OH).

Recent advances in electrocatalysis with phthalocyanines

Applications of phthalocyanines (Pcs) in electrocatalysis-including the oxygen reduction reaction (ORR), the carbon dioxide reduction reaction (CO₂RR), the oxygen evolution reaction (OER), and the hydrogen evolution reaction (HER)-have attracted considerable attention recently. Pcs and their derivatives are more attractive than many other macrocycles as electrocatalysts since, although they are structurally related to natural porphyrin complexes, they offer the advantages of low cost, facile synthesis and good chemical stability. Moreover, their high tailorability and structural diversity mean Pcs have great potential for application in electrochemical devices. Here we review the structure and composition of Pcs, methods of synthesis of Pcs and their analogues, as well as applications of Pc-based heterogeneous electrocatalysts. Optimization strategies for Pc-based materials for electrocatalysis of ORR, CO₂RR, OER and HER are proposed, based on the mechanisms of the different electrochemical reactions. We also discuss the structure/composition-catalytic activity relationships for different Pc materials and Pc-based electrocatalysts in order to identify future practical applications. Finally, future opportunities and challenges in the use of molecular Pcs and Pc derivatives as electrocatalysts are discussed.

High Yield of CO and Synchronous S Recovery from the Conversion of CO2 and H2S in Natural Gas Based on a Novel Electrochemical Reactor

H₂S and CO₂ are the main impurities in raw natural gas, which needs to be purified before use. However, the comprehensive utilization of H₂S and CO₂ has been ignored. Herein, we proposed a fully resource-based method to convert toxic gas H₂S and greenhouse gas CO₂ synchronously into CO and elemental S by using a novel electrochemical reactor. The special designs include that, in the anodic chamber, H₂S was oxidized rapidly to S based on the I^-/I₃^- cyclic redox system to avoid anode passivation. On the other hand, in the cathodic chamber, CO₂ was rapidly and selectively reduced to CO based on a porous carbon gas diffusion electrode (GDE) modified with polytetrafluoroethylene and cobalt phthalocyanine (CoPc). A high Faraday efficiency (>95%) toward CO was achieved due to the enhanced mass transfer of CO₂ on the GDE and the presence of the selective CoPc catalyst. The maximum energy efficiency of the system was more than 72.41% with a current density of over 50 mA/cm², which was 12.5 times higher than what was previously reported on the H₂S treatment system. The yields of S and CO were 24.94 mg·cm^-2·h^-1 and 19.93 mL·cm^-2·h^-1, respectively. A model analysis determined that the operation cost of the synchronous utilization of H₂S and CO₂ method was slightly lower than that of the single utilization of H₂S in the existing natural gas purification technology. Overall, this paper provides efficient and simultaneous conversion of H₂S and CO₂ into S and CO.

Iron Phthalocyanine/Two-Dimensional Metal-Organic Framework Composite Nanosheets for Enhanced Alkaline Hydrogen Evolution

Hydrogen evolution reaction (HER) in alkaline medium is currently under scientific spotlight for generating clean H₂ fuel from electrochemical water splitting. However, alkaline HER suffers from sluggish reaction kinetics because of the additional energy required for water dissociation from catalysts in contrast to acidic HER. Herein, we report the development of two-dimensional metal-organic framework (2D MOF) Ni-1,4-benzenedicarboxylic acid-based composite nanosheets for superior performance in HER electrocatalysis. Iron phthalocyanine (FePc) molecules are uniformly anchored on the ultrathin 2D Ni-MOF, showing a substantially increased current density, improved activity, and enhanced durability in alkaline HER. On account of the ultralarge specific surface of Ni-MOF and the coupling effects between FePc and 2D MOFs, the resultant nanosheet catalyst FePc@Ni-MOF exhibits a low overpotential (334 mV) and satisfactory long-term stability (10 h) at a current density of 10 mA·cm^-2, which outperform those of pristine FePc, Ni-MOF, and the counterpart FePc@bulk-MOF. This study provides new insights into the synthesis of robust MOF-based nanosheet composites with high performance in catalysis.

Multilayer stabilization for fabricating high-loading single-atom catalysts

Metal single-atom catalysts (M-SACs) have emerged as an attractive concept for promoting heterogeneous reactions, but the synthesis of high-loading M-SACs remains a challenge. Here, we report a multilayer stabilization strategy for constructing M-SACs in nitrogen-, sulfur- and fluorine-co-doped graphitized carbons (M = Fe, Co, Ru, Ir and Pt). Metal precursors are embedded into perfluorotetradecanoic acid multilayers and are further coated with polypyrrole prior to pyrolysis. Aggregation of the metals is thus efficiently inhibited to achieve M-SACs with a high metal loading (~16 wt%). Fe-SAC serves as an efficient oxygen reduction catalyst with half-wave potentials of 0.91 and 0.82 V (versus reversible hydrogen electrode) in alkaline and acid solutions, respectively. Moreover, as an air electrode in zinc–air batteries, Fe-SAC demonstrates a large peak power density of 247.7 mW cm⁻² and superior long-term stability_. Our versatile method paves an effective way to develop high-loading M-SACs for various applications.

Metal single-atom catalysts offer great potential in bridging the gap between heterogeneous and homogeneous catalysis. Here the authors demonstrate a multilayer stabilization strategy for fabricating high-loading single-atom catalysts including non-precious and noble metals.

Enhancing the water splitting performance via decorating Co3O4 nanoarrays with ruthenium doping and phosphorization

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co₃O₄ nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm⁻² for HER and 342 mV at 50 mA cm⁻² for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

CoRuPO/NF shows low overpotentials in HER and OER.

From polymeric carbon nitride to carbon materials: extended application to electrochemical energy conversion and storage

As an emerging photocatalyst, polymeric carbon nitride (PCN) currently has drawn ever-increasing attention for electrochemical energy conversion and storage due to its graphite-like structure, metal-free characteristic and excellent structural tunability. Nonetheless, its practical applications are still hindered by the poor electrical conductivity induced irreversible capacity loss. Recently, PCN-derived carbon materials with improved conductivity have received increasing interest and made tremendous progress for advanced electrochemical energy conversion and storage. This review highlights the latest research advancements regarding the electrochemical energy conversion (hydrogen evolution reaction, oxygen reduction/evolution reaction, nitrogen reduction reaction, carbon dioxide reduction reaction, etc.) and storage (Li-ion batteries, Li-S batteries, supercapacitors, etc.) application from PCN to PCN-derived carbon materials. A perspective about the challenges and trends in the electrochemical application of PCN and PCN-derived carbon materials is also provided at the end of the review.

Hydrogen Evolution Reaction-From Single Crystal to Single Atom Catalysts

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

CoOx(OH)y/C nanocomposites in situ derived from Na4Co3(PO4)2P2O7 as sustainable electrocatalysts for water splitting

An original electrode design strategy for water splitting was considered. Electrodes covered by CoO_x(OH)_y/C nanocomposites were in situ fabricated. Assembled CoO(OH)/C∥Co(OH)₂/C system reveals excellent long-time stability (more than 50 hours at 10 mA cm⁻²) with the total overpotential of 0.6 V.