Low-cost Catalysts Research Articles

Hydrogen Peroxide Electrosynthesis in a Strong Acidic Environment Using Cationic Surfactants.

The two-electron oxygen reduction reaction (2e--ORR) can be exploited for green production of hydrogen peroxide (H2O2), but it still suffers from low selectivity in an acidic electrolyte when using non-noble metal catalysts. Here, inspired by biology, we demonstrate a strategy that exploits the micellization of surfactant molecules to promote the H2O2 selectivity of a low-cost carbon black catalyst in strong acid electrolytes. The surfactants near the electrode surface increase the oxygen solubility and transportation, and they provide a shielding effect that displaces protons from the electric double layer (EDL). Compared with the case of a pure acidic electrolyte, we find that, when a small number of surfactant molecules were added to the acid, the H2O2 Faradaic efficiency (FE) was improved from 12% to 95% H2O2 under 200 mA cm-2, suggesting an 8-fold improvement. Our in situ surface enhanced Raman spectroscopy (SERS) and optical microscopy (OM) studies suggest that, while the added surfactant reduces the electrode's hydrophobicity, its micelle formation could promote the O2 gas transport and its hydrophobic tail could displace local protons under applied negative potentials during catalysis, which are responsible for the improved H2O2 selectivity in strong acids.

Non-Noble Metal High-Entropy Alloy-Based Catalytic Electrode for Long-Life Hydrogen Gas Batteries.

The development of efficient, stable, and low-cost bifunctional catalysts for the hydrogen evolution/oxidation reaction (HER/HOR) is critical to promote the application of hydrogen gas batteries in large scale energy storage systems. Here we demonstrate a non-noble metal high-entropy alloy grown on Cu foam (NNM-HEA@CF) as a self-supported catalytic electrode for nickel-hydrogen gas (Ni-H2) batteries. Experimental and theoretical calculation results reveal that the NNM-HEA catalyst greatly facilitates the HER/HOR catalytic process through the optimized electronic structures of the active sites. The assembled Ni-H2 battery with NNM-HEA@CF as the anode shows excellent rate capability and exceptional cycling performance of over 1800 h without capacity decay at an areal capacity of 15 mAh cm-2. Furthermore, a scaled-up Ni-H2 battery fabricated with an extended capacity of 0.45 Ah exhibits a high cell-level energy density of ∼109.3 Wh kg-1. Moreover, its estimated cost reaches as low as ∼107.8 $ kWh-1 based on all key components of electrodes, separator and electrolyte, which is reduced by more than 6 times compared to that of the commercial Pt/C-based Ni-H2 battery. This work provides an approach to develop high-efficiency non-noble metal-based bifunctional catalysts for hydrogen batteries in large-scale energy storage applications.

Heteroatom-Doped Carbon-Based Catalysts Synthesized through a “Cook-Off” Process for Oxygen Reduction Reaction

The development of efficient and low-cost non-metallic catalysts is of great significance for the oxygen reduction reaction (ORR) in fuel cells. Heteroatom-doped carbon-based catalysts are one of the popular candidates, although their preparation method is still under exploration. In this work, single (CS)-, double (NCS)-, and triple (NBCS)-heteroatom-doped carbon-based catalysts were successfully prepared by a “cook-off” process. The morphology, elemental composition, and bonding structure of the catalysts were investigated by SEM, TEM, Raman spectra, BET, and XPS. ORR catalytic performance measurements suggested an activity trend of CS < NCS < NBCS, and NBCS demonstrated better methanol resistance and slightly higher stability than the commercial Pt/C catalyst, as evaluated with both rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) systems. The mechanism for the promoted performance was also proposed based on the conductivity of the catalysts. In this paper, the heteroatoms N, B, and S were co-doped into activated carbon using a simple, fast, and efficient preparation method with high electrical conductivity and also increased active sites, showing high electrocatalytic activity and good stability. This work provides a new approach to preparing highly active non-Pt catalysts for oxygen reduction reactions.

Elucidating the structure-activity relationship of the bimetallic Ni-Cu catalysts for CO2 hydrogenation

The conversion of carbon dioxide (CO2) into high-value products plays a critical role in mitigating atmospheric CO2 levels. Recently, low-cost Ni-based catalysts have been garnering attention due to their exceptional hydrogenation ability. This study focuses on the synthesis of Cu-Ni bimetallic catalysts for CO2 hydrogenation and the systematic evaluation of the relationship between structural evolution and catalytic activity. Through investigation of the selectivity regulation of Cu on Ni-based catalysts, it was discovered that the addition of Cu led to a significant shift in catalytic activity and selectivity. Specifically, the Cu addition transitioned the reaction from being CH4-selective to CO-selective. Moreover, the introduction of Cu preferentially generated a Cu-Ni alloy during the reaction, which resulted in a significant number of *CO species with strong adsorption strength at the interface. Consequently, the subsequent hydrogenation of these *CO species was impeded, rendering the catalyst CO-selective.

Solvent-free synthesis of foam board-like CoSe2 alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation

Singlet oxygen (1O2) is a highly effective reactive species in selectively oxidizing organic pollutants. However, it is still challenging to rationally design robust catalysts for the selective generation of 1O2. Herein, the coordination and engineering architecture of the foam board-like CoSe2 alloy were facilely constructed through a green solvent-free method and displayed almost 100% 1O2 production selectivity. The CoSe2 alloy showed excellent catalytic ability for the efficient and fast removal of organic pollutants via peroxymonosulfate (PMS) activation compared with previously reported cobalt-based catalysts. The CoSe2/PMS system exhibited strong resistance for a broad pH range (3.0–11.0) and various coexisting inorganic ions owing to the advantage of the strong bonding of Co-Se in CoSe2 alloy. Mechanism studies revealed that 1O2 was the only reactive oxygen species in the CoSe2/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe2, and the production pathway of 1O2 was PMS* → *OH → *O → 1O2. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of 1O2 by PMS activation on CoSe2 alloy. These findings provide a rational strategy for preparing a series of low-cost transition metal-based alloy catalysts for PMS activation to achieve high-efficiency 1O2 production in the elimination of organic pollutants.

Biomass-derived nitrogen-doped carbons activated by zinc halides for electrocatalytic oxygen reduction reaction

Biomass-derived carbon materials are certified to be excellent catalysts for oxygen reduction reaction (ORR) and their ORR activity is severely affected by activators. For this reason, three zinc halides (ZnF2, ZnBr2, and ZnI2) and ZnCl2 used as activators for the formation of pea pod-derived carbon materials are systematically investigated for the first time. The presence of ZnX2 significantly changes the morphology of biomass-derived carbon materials and effectively increases the specific surface area, surface defect and doping content of N. These factors effectively promote the ORR activity of the product, especially PPBrNC. The four resulted carbons show high onset potential, half-wave potential and limiting current density that is comparable with Pt/C, and the obvious 4-electron reduction pathway is displayed in ORR process. Meanwhile, the ultra-high stability and methanol tolerance make it a potential non-precious metal catalyst. Therefore, ZnX2 is a class of low-cost and excellent chemical activators for the preparation of biomass-derived carbon materials and can provide a new idea for exploring low-cost, efficient and stable ORR catalysts.

Photo-Fenton efficient degradation of organic pollutants over S-scheme ZnO@NH2-MIL-88B heterojunction established for electron transfer channel

Combining photocatalysts with Fenton technology can improve the catalytic properties of materials and achieve efficient degradation of organic pollutants. However, preparing low-cost catalysts using simple methods remains a challenge. This paper selected a more environmentally friendly and cost-effective semiconductor material, zinc oxide, for the modification of NH2-MIL-88B and prepared a new S-scheme heterojunction photo-Fenton catalyst ZnO@NH2-MIL-88B (ZMFe-x) by a simple solvothermal method. Moreover, the Zn-O-Fe bonds that were formed between the interfaces enabled a fast channel for the photoelectron transport that was created by photoexcitation from the ZnO conduction band to the NH2-MIL-88B valence band. This allowed the ZMFe-x catalysts to have better removal performance for organic pollutants in the photo-Fenton reaction. The dominating role of hydroxyl radicals in the degradation procedure was determined by ESR analysis and free radical trapping experiments, and the degradation mechanisms and pathway of contaminants were predicted by intermediate analysis and DFT calculations. This study provides a stable and effective new strategy for preparing MOFs catalysts for removing various pollutants.

Le Chatelier’s principle to stabilize intrinsic surface structure of oxygen-evolving catalyst for enabling ultra-high catalytic stability of zinc-air battery and water splitting

Well-designed highly active intrinsic surface structure of a catalyst for oxygen evolution reaction (OER) often faces the problem of corrosion dissolution, which severely deteriorates its catalytic stability, and breaking this activity-stability trade-off has always been a huge and long-term challenge. Herein, we employ Le Chatelier’s principle to address this dissolution problem of the catalyst to maintain its intrinsic surface structure for highly efficient and ultra-stable OER. Taking highly active but susceptible oxygen vacancy-rich Co-W oxide as the model catalyst for alkaline OER, its dissolving kinetics is significantly passivated by introducing homo ions into the electrolyte to regulate the dissolution equilibrium, thus achieving ultralong operating stability without sacrificing its high activity. The theoretical calculations and in-situ experimental results unravel the underlying mechanism of this strategy, that is, the homo ions (tungstate ions) can be preferentially adsorbed on the catalyst surface to construct a local non-corrosive environment, thus effectively stabilizing the well-designed unsaturated active cobalt sites to maintain the intrinsic surface structure of the catalyst and preventing them from being reconstructed or transformed toward the unfavorable direction. Importantly, this strategy is also effective in zinc-air battery and electrolytic water splitting, achieving ultra-stable performance over 1200 h, which is of great importance for promoting the practical applications of low-cost non-noble metal-based catalysts in energy devices.

A Sulfur-Doped Copper Catalyst with Efficient Electrocatalytic Formate Generation during the Electrochemical Carbon Dioxide Reduction Reaction.

Catalysts involving post-transition metals have shown almost invincible performance on generating formate in electrochemical CO2 reduction reaction (CO2 RR). Conversely, Cu without post-transition metals has struggled to achieve comparable activity. In this study, a sulfur (S)-doped-copper (Cu)-based catalyst is developed, exhibiting excellent performance in formate generation with a maximum Faradaic efficiency of 92 % and a partial current density of 321 mA cm-2 . Ex situ structural elucidations reveal the presence of abundant grain boundaries and high retention of S-S bonds from the covellite phase during CO2 RR. Furthermore, thermodynamic calculations demonstrate that S-S bonds can moderate the binding energies with various intermediates, further improving the activity of the formate pathway. This work is significant in modifying a low-cost catalyst (Cu) with a non-metallic element (S) to achieve comparable performance to mainstream catalysts for formate generation in industrial grade.

Copper oxide nanofibers obtained by solution blow spinning as catalysts for oxygen evolution reaction

In this work, we report copper oxide nanofibers (CuO – N) synthesized by Solution Blow Spinning (SBS) for oxygen evolution reaction (OER), and their comparison with a control sample based on a commercial powder (CuO – C). Both materials were characterized by various techniques, including X-ray diffraction (XRD), magnetometry, scanning electron microscopy (SEM), and spectroscopy (Fourier transform infrared (FT-IR), Raman and X-ray photoelectron (XPS)) to determine the purity, microstructural and surface chemical properties. Subsequently, the performance of copper oxide catalysts in a 1.0 M KOH solution was investigated. Copper oxide with nanofiber morphology (CuO – N) exhibited a small overpotential of 385 mV @ 10 mA cm−2 and a Tafel coefficient of only 76 mV dec−1, i.e., fast kinetics for water splitting, a result that is modulated by oxygen vacancies (O2/O1 = 0.83). The oxygen vacancies are due to the presence of Cu1+ in the lattice. The analyses of the magnetization measurements at 5 K suggest a larger amount of Cu1+ in sample CuO – N. Therefore, this work sheds light on how to design low-cost nanofibrous catalysts based on abundant transition metals in the earth's crust by SBS, an economical and scalable technique, which is promising for energy applications.

Rational Photodeposition of Cobalt Phosphate on Flower-like ZnIn2S4 for Efficient Photocatalytic Hydrogen Evolution.

The high electrons and holes recombination rate of ZnIn2S4 significantly limits its photocatalytic performance. Herein, a simple in situ photodeposition strategy is adopted to introduce the cocatalyst cobalt phosphate (Co-Pi) on ZnIn2S4, aiming at facilitating the separation of electron-hole by promoting the transfer of photogenerated holes of ZnIn2S4. The study reveals that the composite catalyst has superior photocatalytic performance than blank ZnIn2S4. In particular, ZnIn2S4 loaded with 5% Co-Pi (ZnIn2S4/5%Co-Pi) has the best photocatalytic activity, and the H2 production rate reaches 3593 μmol·g-1·h-1, approximately double that of ZnIn2S4 alone. Subsequent characterization data demonstrate that the introduction of the cocatalyst Co-Pi facilitates the transfer of ZnIn2S4 holes, thus improving the efficiency of photogenerated carrier separation. This investigation focuses on the rational utilization of high-content and rich cocatalysts on earth to design low-cost and efficient composite catalysts to achieve sustainable photocatalytic hydrogen evolution.

Controlled doping of ultralow amounts Ru on Ni cathode for PEMWE: Experimental and theoretical elucidation of enhanced performance

Proton exchange membrane water electrolysis (PEMWE) is an environmentally benign technology for large-scale hydrogen production. Despite many catalysts being developed to replace Pt, successful development of low-cost catalysts that meet the balance of performance and durability is limited. In this work, atomically dispersed Ru on Ni catalyst-integrated porous transport electrodes were fabricated by a simple electrodeposition. With a trace amount of Ru (< 0.05 mgRu·cm−2), the Ni98.1Ru1.9 cathode catalyst exhibited an overpotential of 35 mV at –10 mA·cm−2 with excellent stability. Density functional theory calculation revealed that the high performance was driven by optimized adsorption strength and improved mobility of hydrogen on the catalyst surface. The Ni98.1Ru1.9 electrode was further verified in a PEMWE cell and resulting performance (6.0 A·cm−2 at 2.25 Vcell) and stability (0.13 mV·h−1 decay rate at 1 A·cm−2) surpassed previously reported non-Pt and even Pt electrodes, demonstrating its readiness as an advanced cathode to replace Pt.

Degradation of the cytostatic drug bicalutamide by photo-assisted catalytic wet peroxide oxidation

The presence of cytostatic drugs, such as bicalutamide (BICA), in aquatic compartments reveals the necessity of developing efficient processes for their elimination in wastewater treatment plants (WWTP). This work explores for the first time the use of natural magnetite as a low-cost catalyst in the photo assisted — catalytic wet peroxide oxidation (UV-CWPO) of BICA. For this purpose, real WWTP secondary effluents were spiked with 100 μg/L BICA and subjected to UV-CWPO. Preliminary runs comparing UV photolysis, UV/H2O2, CWPO and UV-CWPO confirmed the synergistic effect of UV radiation and the CWPO process employing magnetite. Afterwards, a parametric study was performed evaluating the influence of the pH, catalyst load, H2O2 dosage, temperature and water matrix. Under optimum operating conditions (pH 0: 6, [magnetite]: 375 mg/L and [H2O2]: 75 mg/L), 99.7 % BICA degradation and 60.7 % mineralization were reached after 30 min in WWTP effluent. UV-CWPO also proved to be effective in hospital wastewater. Catalyst activity was studied in 5 consecutive runs, showing great stability for both BICA removal and TOC elimination. Finally, phytotoxicity tests revealed a lower toxicity in the UV-CWPO effluent compared to the untreated stream. Hence, UV-CWPO proved to be a feasible to eliminate risky cytostatic drugs in relevant environmental matrices.

An organic–inorganic hybrid method to fabricate bimetallic phosphide nanospheres as efficient electrocatalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) serves as a crucial half reaction in electrolytic water splitting. Pt is deemed to the most active HER electrocatalyst, but the scarcity and high cost of Pt limit its massive application. Developing efficient, low-cost and well-structured HER catalysts is quite vital for advancing the development of water electrolysis technology. Herein, we present a facile organic–inorganic hybrid method to achieve a novel bimetallic phosphide of MoP-RuPx/NPC catalyst, showing superior electrocatalytic activity with an overpotential of 24 and 94 mV at 10 mA cm−2 in alkaline and acid media, respectively. Moreover, MoP-RuPx/NPC also exhibits an outstanding electrochemical stability with a negligible degradation in HER activity after long-term stability measurements. The eminent electrocatalytic performance of MoP-RuPx/NPC catalyst should be ascribed to the high surface specific area, multiple heterogeneous interfaces, strong electronic synergistic effect between MoP and RuPx, and abundant defects. The organic–inorganic hybrid strategy implemented in this work can be used for synthesizing other bimetallic phosphide catalysts.

Molecular sieve-like wood achieves efficient chiral catalysis

Molecular sieve catalysts have been adopted in chiral catalytic reactions due to their high specific surface area, nano-scaled pores and effective separation, however, the problems like low utilization ratio of channels, difficult modification, long period and complex preparation, and no economic benefits reduce its widely application. In this paper, natural wood was employed as raw material to preserve the cellulose skeleton rich in poly‑hydroxyl and the multistage porous channels of nanometer, micron and millimeter by simple treatment. A low-cost, high-yield and high-selectivity chiral catalyst could be obtained from wood with chiral catalytic sites. The in situ grafting method retains the well-developed multistage pore structure of wood, enhances the mass transfer and possesses universal applicability to different aldol condensation reactions. The asymmetric reaction of cyclohexanone and p-nitrobenzaldehyde is catalyzed by grafting readily available amino acids such as threonine, with a yield of 82% and selectivity of 57%. Molecular sieve-like wood possesses the advantages of low economic cost and good catalytic performance, which provides a potential possibility to replace traditional molecular sieve catalyst.

Constructing fully exposed Pt atomically dispersed catalysts for enhanced multifunctional selective hydrogenation reactions

Constructing highly efficient and low-cost catalysts is essential for the selective hydrogenation reaction. Herein, we developed fully exposed Pt atomically dispersed catalysts (PtAD/C-Al2O3) by a simple carbon modified strategy. Importantly, the co-existence of Pt-O1C2 single atoms and Pt nanoclusters in the PtAD/C-Al2O3 system could exhibit excellent catalytic activity in the selective hydrogenation of quinoline and p-nitrophenol. Notably, the quinoline conversion and the corresponding selectivity of 1,2,3,4-tetrahydroquinoline is 99.6 % and 99.3 %, respectively. Meanwhile, the turnover frequency of PtAD/C-Al2O3 (1081 h−1) is 3.8 and 5.7 times higher than that of Pt single-atom catalysts (PtSA/C-Al2O3) and Pt nanoparticles (PtNPs/C-Al2O3), respectively, during quinoline hydrogenation. Besides, the rate constant of PtAD/C-Al2O3 could reach 192.5 min-1mgPt-1 for p-nitrophenol hydrogenation, which is much better than most of the reported catalysts. Mechanism studies revealed the synergistic effect between Pt-O1C2 single atoms and Pt nanoclusters acts as the main role in enhancing the hydrogenation activity. Specifically, Pt single atoms sites mainly adsorb and activate quinoline molecules, while Pt nanoclusters boost the dissociation of H2 molecules to H atoms. This work paves an origin carbon modified method to construct Pt atomically dispersed catalysts for efficient multifunctional hydrogenation.

Modeling TiO2/UV–vis bacterial inactivation: Useful tools for reactor optimization and design

Heterogeneous photocatalysis applying TiO2 based catalysts has been widely studied for removing inorganic and organic compounds from water and for bacterial inactivation. This available and low-cost catalyst has demonstrated to be effective in the removal of organic pollutants and inactivation of pathogenic bacteria from water. The design of proper types of industrial-scale photoreactors has not been yet successfully implemented, probably due to the conceptual complexity of modeling this process in real wastewater. As a result, TiO2 based photocatalysis is still considered an effective but energetic-inefficient process. In this work, Escherichia coli (gram-positive) and Enterococcus sp (gram-negative) were selected for studying the kinetics of TiO2 photocatalysis. Since several approaches, such as fist-order kinetics, are not truly representative of the bacterial inactivation process, the experimental data were fitted to different mathematical models, such as Gompertz model, which has demonstrated to describe the process properly. Moreover, the effect of the main variables of the process in the inactivation kinetic constant of the Gompertz model has ben studied. More precisely, light intensity, water matrix, catalyst concentration and bacteria have been under study and their effect has been included in the kinetic equation. Finally, operational and construction parameters of a 20 m3/d annular photoreactor for bacterial inactivation has been successfully optimized applying the proposed kinetic model.

Fe-Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media.

NiFe-based oxo-hydroxides are highly active for the oxygen evolution reaction but require complex synthesis and are poorly durable when deposited on foreign supports. Herein we demonstrate that easily processable, Earth-abundant and cheap Fe-Ni alloys spontaneously develop a highly active NiFe oxo-hydroxide surface, exsolved upon electrochemical activation. While the manufacturing process and the initial surface state of the alloys do not impact the oxygen evolution reaction performance, the growth/composition of the NiFe oxo-hydroxide surface layer depends on the alloying elements and initial atomic Fe/Ni ratio, hence driving oxygen evolution reaction activity. Whatever the initial Fe/Ni ratio of the Fe-Ni alloy (varying between 0.004 and 7.4), the best oxygen evolution reaction performance (beyond that of commercial IrO2) and durability was obtained for a surface Fe/Ni ratio between 0.2 and 0.4 and includes numerous active sites (high NiIII/NiII capacitive response) and high efficiency (high Fe/Ni ratio). This knowledge paves the way to active and durable Fe-Ni alloy oxygen-evolving electrodes for alkaline water electrolysers.

Ce Single-Atom Incorporation Enhances the Oxygen Evolution Reaction of Co3O4 in Acid.

Oxygen evolution reaction (OER) plays an important role in energy conversion processes such as water electrolysis and metal-air batteries. At present, finding a high-performance and low-cost catalyst for the OER in acidic media remains a great challenge. It is therefore important to develop efficient, robust, and inexpensive electrocatalysts by replacing noble metal-based catalysts with transition-metal electrocatalysts. Herein, we propose a facile method for incorporating Ce-metal single atoms into Co3O4 nanosheets to boost their OER activity and stability. Owing to the enhanced charge transfer and improved electronic structure resulting from Ce incorporation, the obtained Ce single-atom-doped Co3O4 nanosheet exhibits greatly enhanced OER performance. It achieves a 10 mA cm-2 current density under a low overpotential of 348 mV in a 0.5 M H2SO4 solution with excellent stability, outperforming the state-of-the-art non-noble electrocatalysts recently reported in acid.

From byproducts to bioresources: cocoa shell solid-state fermentation lipase as a low-cost esterification catalyst

From byproducts to bioresources: cocoa shell solid-state fermentation lipase as a low-cost esterification catalyst