CO Impurities Research Articles

Ru-embedded TiO2-x with rich Ru-Ti bonds and triggered oxygen vacancies for boosted and sustained hydrogen oxidation and evolution electrocatalysis in alkaline medium

The sluggish hydrogen energy conversion kinetics in alkaline medium and the complete passivation under high anodic potential as well as the easy detachment of active sites from the carbon substrate are three critical challenges of Ru-based electrocatalysts for their practical application. Herein, Ru (single atoms and nanoclusters)-embedded TiO2-x (RuSA-RuNC/TiO2-x) well solves above-mentioned urgent problems simultaneously. Specifically, the optimal RuSA-RuNC/TiO2-x electrocatalyst delivers a mass activity of 1620 A gRu–1 and a low overpotential of 24 mV at 10 mA cm−2 in alkaline hydrogen oxidation and evolution reactions (HOR/HER), respectively. More importantly, the Ru/TiO2-x can unprecedentedly catalyze the HOR up to a potential of 1.2 V vs. RHE without deactivation and almost maintain unchanged after accelerated stability tests of 10,000 CVs or the presence of 100 ppm CO impurity. Confirmed by in/ex-situ experimental measurements and computational analyses, the enhancement in performance is attributed mainly to the construction of high-density Ru-Ti bonds, maintaining the unblocked charge transfer from TiO2 to Ru and achieving more low-valence Ru species. The observed Ti3+ species on oxygen vacancies derived from the original structure and in-situ formation during the electrochemical reaction would be preferentially oxidized, further protecting Ru sites and aiding in the electrocatalytic process. Benefiting from Ru-Ti bonds and triggered oxygen vacancies, Ru could serve as exclusive optimal H adsorption sites and cooperate with the OHad on Ti sites, rapidly and stably accelerating hydrogen energy conversion.

Enhancing CO tolerance in hydrogen oxidation reaction through synergy of surface-modified MoOx with PtRu alloy

Even trace amounts of CO impurities present in low-cost crude hydrogen can severely poison Pt-based catalysts. For proton exchange membrane fuel cells (PEMFCs), the development of hydrogen oxidation reaction (HOR) catalysts capable of enduring CO contamination is of significant economic importance. In this study, we propose a new strategy to synergistically enhance the CO tolerance of PtRu alloys by incorporating MoOx. The MoOx modified on PtRu/C catalysts can initiate the oxidation of CO adsorbed on its surface at potentials as low as 0.125 V. The synergy effect of MoOx and bifunctional PtRu ensures sufficient HOR stability even under hydrogen containing high CO concentrations. The resulting PtRu-MoOx/C catalyst exhibits a 4.6-fold increase in the remained HOR current compared with commercial PtRu/C, after two hours in a hydrogen environment containing 10,000 ppm CO. Under typical testing condition of H2/1,000 ppm CO, PtRu-MoOx/C maintains over 80% of the initial current density even after ten hours, significantly outperforming PtRu/C (30%) and most previously reported catalysts.

Atomic insights into the corrosion behavior of Fe-Cr alloys in supercritical CO2 environment

In this work, the corrosion process of Fe-Cr alloys in flowing CO2 was simulated using molecular dynamics within an extended ReaxFF force field. The effects of Cr content, temperature variations, impurity gases and vacancy defects were discussed. The corrosion process was dominated by oxidation and carburization reactions, with the oxidation rate higher than carburization rate, resulting in the formation of a carbide layer within the central region between two oxide layers. The increase in Cr content tended to decelerate corrosion, while raising temperature aggravated the corrosion of Fe-Cr alloy. The presence of O2 and SO2 impurities was found to thicken the corrosion layer, in contrast to the effects of CO and H2O impurities. A notable finding highlighted the positive influence of 2% vacancy defects in enhancing the corrosion resistance of the Fe-Cr alloy. The Al2O3 coating achieved a good corrosion protection by inhibiting the dissociation of CO2.

High density ultra-small Cu nanoparticles with abundant oxygen vacancies for efficient hydrogen evolution from MeOH/H2O

Efficient release of H2 with negligible CO impurities from sustainable MeOH/H2O has become a promising goal for on-board hydrogen generator. However, hydrogen release kinetics still face challenges. In this work, the Cu/ZnO/CeO2 catalyst with high density ultra-small Cu nanoparticles and abundant oxygen vacancies were prepared for intensifying hydrogen evolution in aqueous phase reforming of methanol (APRM). The optimized 55% Cu/ZnO/CeO2 catalyst (Cu NPs of 3.8 nm, Cu loading of 55.89 wt%, oxygen vacancies of 2.316 × 1015 spins g−1) exhibited an excellent H2 evolution rate of 58.39 μmolgcat−1 s−1 even at low temperature of 210 °C, which was 2.1-fold enhancement than that of commercial Cu/ZnO/Al2O3 catalyst. Characterizations and experiments revealed that ZnO/CeO2 intensified the strong metal-support interaction (SMSI), which anchored the Cu NPs, generated abundant oxygen vacancies and adjusted electronic structure to form Cu0-Cu+-Ov active sites for facilitating the kinetics of APRM.

Carbon monoxide impurities in hydrogen detected with resonant photoacoustic cell using a mid-IR laser source

We report on a photoacoustic sensor system based on a differential photoacoustic cell to detect the concentration of CO impurities in hydrogen. A DFB-QCL laser with a central wavelength of 4.61 µm was employed as an exciting source with an optical power of 21 mW. Different concentrations of CO gas mixed with pure hydrogen were injected into the photoacoustic cell to test the linear response of the photoacoustic signal to the CO concentration. The stability of the long-term operation was verified by Allan-Werle deviation analysis. The minimum detection limit (MDL, SNR=1) results 8 ppb at 1 s and reaches a sub-ppb level at 100 s of integration time. Dynamic response of the system is linear and has been tested up to the concentration of 6 ppm. Saturation conditions are expected to be reached for CO concentration larger than 100 ppm.

Effects of chemisorption impurities on hydrogen diffusion mechanism from Pd(100) surface into subsurface

The impurities exhibit a remarkable impact on adsorption, absorption, and diffusion behavior of hydrogen on catalyst surface, and prompt an essential ongoing challenge on security and development strategy in hydrogen production, separation, purification, and utilization. Given this, S and CO impurities accompanied with or without atomic hydrogen, i.e. S, S + H, CO, and CO + H, were focused to discreetly elucidate their influences on microscopic mechanism for hydrogen travelling into Pd(100) subsurface in terms of spatial orientations and distinct coverages. All viable minimum energy pathways were thoroughly explored by climbing image nudged elastic band method, in which substrate relaxation and reconstruction effects were considered. Quantum results manifest that S or CO overwhelmingly changes structural and electrical properties of metal surface, and thus facilitates hydrogen diffusion, except for ones on H3 site at 0.25 ML coverage. Whereas, H in both S + H and CO + H shows inhibition effect by increasing barrier and blocking active surface site.

Understanding the Effects of Transition Metal Impurities on Nickel (oxy) Hydroxide Electrocatalysts in Alkaline Media

Nickel-based materials are widely used as critical components of electrochemical energy devices, including alkaline electrolyzers, capacitors, and alkaline batteries. These materials are often preferred because of their availability and low cost compared to precious metals, which makes them excellent candidates for accomplishing the decarbonization goals and electrifying our society. However, several studies have demonstrated that the incorporation of trace impurities from commercial alkaline electrolytes induces significant changes in the intrinsic activity, pseudocapacitance, and stability of Ni-based materials, resulting in erroneous descriptions of their performance. Thus, having a better understanding of the effects of these impurities will lead to practical ways to prevent or control their impact on electrochemical energy devices.In this work, we study the incorporation of transition metals (i.e., Fe, Co, Cu) that form insoluble hydroxides in alkaline media over nickel (oxy) hydroxide electrocatalysts. We systematically examine how these trace impurities modify the OER activity, stability, and the pseudocapacitive properties of NiOOH. As depicted in Figure 1, KOH electrolytes containing trace impurities of Fe and Co induce significant changes in the OER onset potential of Ni(OH)2/NiOOH electrocatalysts, according to the irreversible charge increase measured through coulovoltammetry (QV) curves. Moreover, distinct redox peaks can be seen for each scenario. After aging in purified KOH electrolyte (Fig. 1a), the cyclic voltammogram (CV) of Ni(OH)2/NiOOH exhibits four oxidation peaks that can be ascribed to a mixture of both α and β structural phases (Fig. 1b) while aging in Fe-unpurified KOH promotes the α phase and shifts the redox peak anodically (Fig. 1c). Aging in Co-unpurified KOH promotes a more ordered β structural phase without changing the OER activity significantly (Fig. 1d), which is desirable for pseudocapacitive materials. Additional experiments examining the OER activity, stability, and capacitance provide valuable insights into these impurities, and specific strategies to prevent and minimize their effects will be discussed. Overall, this work illustrates the importance of tracking trace metal impurities in alkaline electrolytes to minimize undesirable effects in electrochemical energy devices. Figure 1

Mg-incorporated sorbent for efficient removal of trace CO from H2 gas

Removal of trace CO impurities is an essential step in the utilization of Hydrogen as a clean energy source. While various solutions are currently employed to address this challenge, there is an urgent need to improve their efficiency. Here, we show that a bead-structured Mg, Cu, and Ce-based sorbent, Mg13CuCeOx, demonstrates superior removal capacity of trace CO from H2 with high stability. The incorporation of Mg boosts sorption performance by enhancing the porous structure and Cu+ surface area. Remarkably, compared to existing pelletized sorbents, Mg13CuCeOx exhibits 15.5 to 50 times greater equilibrium capacity under pressures below 10 Pa CO and 31 times longer breakthrough time in removing 50 ppm CO in H2. Energy-efficient oxidative regeneration using air at 120 °C allows its stable sorption performance over 20 cycles. Through in-situ DRIFTS analysis, we elucidate the reaction mechanism that Mg augments the surface OH groups, promoting the formation of bicarbonate and formate species. This study highlights the potential of MgCuCeOx sorbents in advancing the hydrogen economy by effectively removing trace CO from H2.

Co-adsorption of H2+nCO+mO2 on α-Fe (110): Effect on hydrogen adsorption, dissociation and diffusion

Hydrogen enriched compressed natural gas contains CO and O2 impurities, which have a coupling effect on hydrogen adsorption, dissociation and diffusion. First principles plane wave calculations have been used to study the co-adsorption and mutual interaction of H2+nCO + mO2 on Fe (110) plane. The results show that it’s easier for pre-adsorbed nCO + mO2 to form high surface coverage compared with pre-adsorbed nCO or mO2. The CO and O2 increased H2 dissociation barrier (Edis−b), and high coverage of nCO, mO2 and nCO + mO2 increased the hydrogen dissociation activation energy (Edis). With the coverage increased, the diffusion barrier (Edif) of H atom into Fe (110) decreased from 1.01eV to 0 by nCO and increased from 1.01eV to 2.14eV by mO2. The Edif was controlled by CO under low coverage and was controlled by O2 under high coverage when nCO + mO2 pre-adsorbed: the deformation charge density and state density analysis show that in H2+nCO + mO2 system, H atom is in an electron gain state at low coverage, which is similar to H in pre-adsorbed nCO, and H is in an electron loss state at high coverage, which is similar to H in pre-adsorbed mO2.The Edif probably related to the charge interaction of Hx− and Hy+ with Fez+.The C, O and H formant peaks from density of states show the influence of C and O on hydrogen invasion in orbital energy.

Synergic effect investigation of carbon monoxide and other compositions on the high temperature proton exchange membrane fuel cell

The high temperature proton exchange membrane fuel cell integrated with the methanol steam reformer is a promising technology because it avoids the challenges of high pressure hydrogen storage and refueling. The high temperature fuel cell can tolerate the CO content in the methanol reformate with acceptable performance degradation. However, the synergic effects of CO and other impurities in the methanol reformate on the fuel cell performance need further investigation. This study thoroughly evaluates performances of the high temperature proton exchange membrane fuel cell fed in by mixture of H2, CO and other impurities such as CH3OH, H2O and CO2. The transient voltage, polarization curve, and electrical impedance spectroscopy are in-situ measured. The distribution of relaxation times method is used to characterize different time constants in the impedance spectroscopy. Meanwhile, the equivalent circuit model is developed to represent various reaction processes. The results show that the presence of CH3OH with CO in the fuel gas benefits the fuel cell performance at low current densities but aggravates the CO poisoning at high current densities. The addition of H2O with CO decreases both the Ohmic and anodic charge transfer resistances. The combination of CO2 and CO could enhance the effect of CO poisoning. Moreover, the multi-component methanol reformate test results suggest that the coexistence of multiple impurities in the methanol reformate have positive effect on the fuel cell performance.

Valorisation of sulphate rich effluents by electrodialysis

ABSTRACT As part of a route for the valorisation of liquid effluents from copper metallurgical plants, the recovery and generation of sulphuric acid using electrodialysis from synthetic sulphate-rich solutions, similar to those of copper electrometallurgy, was investigated. Sulphate-bearing solution, having sulphuric acid ranging from 45 to 180 g/L and copper from 0 to 40 g/L, and having impurities of Co (0.2 g/L) and Fe (3.0 g/L), were electrodialysed at various current densities at several temperatures. A recovery of sulphuric acid of 0.5 kg/h/m2 was obtained at 300 A/m2 and 55°C, with a final concentration of 216 g/L of high purity H2SO4 with a SEC of 1.95 kWh/kg. Electrodialysis at 700 A/m2 resulted in an acid rate recovery of 1.5 kg/h/m2, with a final concentration of 328 g/L, and a SEC of 2.46 kWh/kg. The mass transport of metal ions and the effect of solution’s viscosity on acid recovery are discussed..

Highly Effective Pt-Co/ZSM-5 Catalysts with Low Pt Loading for Preferential CO Oxidation in H2-Rich Mixture

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH3COO)2 impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N2 sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H2-rich mixture (1%CO + 1%O2 + 49%H2 + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts.

Development of In Situ Formed Metal Pyrophosphates (MP2O7, Where M = Sn, Ti, and Zr)/PA/PBI Based Composite Membranes for Fuel Cells

AbstractDevelopment of high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) at elevated temperatures is important for the enhancement of tolerance toward CO impurities and for the development of non‐precious metal catalysts. The key challenge in such HT‐PEMFCs is the high temperature polymer electrolyte membranes. Herein, the development of in situ formed metal pyrophosphates (MP2O7, where M = Sn, Ti, and Zr) in phosphoric acid doped polybenzimidazole (PA/PBI) composite membranes for HT‐PEMFCs is reported. The formation mechanism of MP2O7, and characteristics of MP2O7/PA/PBI composite membranes are studied in detail. In contrast to the rapid decay in performance of pristine PA/PBI membrane cells, the in situ formed MP2O7/PA/PBI composite membranes show significantly higher proton conductivity, improved performance, and stability at elevated temperatures of 200–250 °C. The best results are obtained on the in situ formed SnP2O7/PA/PBI composite membrane cells, exhibiting a high peak power density of 476 mW cm−2 and proton conductivity of 51.3 mS cm−1 at 250 °C. The excellent durability of SnP2O7/PA/PBI composite membrane is due to the uniform distribution of in situ formed SnP2O7 nanoparticles in PBI membranes and the formation of a gel‐like region, thin and irregular amorphous layer on the SnP2O7 with the high acid retention ability. This effectively alleviates the PA leaching at elevated temperatures of the new HT‐PEMFCs.

Pt Single Atoms on CrN Nanoparticles Deliver Outstanding Activity and CO Tolerance in the Hydrogen Oxidation Reaction.

The large-scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H2 feed. In this context, the development of CO-tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000ppm of CO in H2 feed. The excellent CO-tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO-tolerant catalysts for HOR.

CO-tolerant RuNi/TiO2 catalyst for the storage and purification of crude hydrogen

Hydrogen storage by means of catalytic hydrogenation of suitable organic substrates helps to elevate the volumetric density of hydrogen energy. In this regard, utilizing cheaper industrial crude hydrogen to fulfill the goal of hydrogen storage would show economic attraction. However, because CO impurities in crude hydrogen can easily deactivate metal active sites even in trace amounts such a process has not yet been realized. Here, we develop a robust RuNi/TiO2 catalyst that enables the efficient hydrogenation of toluene to methyl-cyclohexane under simulated crude hydrogen feeds with 1000–5000 ppm CO impurity at around 180 °C under atmospheric pressure. We show that the co-localization of Ru and Ni species during reduction facilitated the formation of tightly coupled metallic Ru-Ni clusters. During the catalytic hydrogenation process, due to the distinct bonding properties, Ru and Ni served as the active sites for CO methanation and toluene hydrogenation respectively. Our work provides fresh insight into the effective utilization and purification of crude hydrogen for the future hydrogen economy.

First-Principles Study of the Effect of Titanium Doping on Carbon Monoxide Poisoning Properties of Zirconium-Cobalt Alloys

It is very important to study impurity gas poisoning in ZrCo alloy because it is associated directly with the performance of ZrCo alloy as a hydrogen storage material. In this work, the effects of atomic replacement on the mechanism and properties of CO impurity gas poisoning in doped (Ti) ZrCo hydrogen storage alloys were investigated using the first principles method, based on the pseudopotential plane wave method. The adsorption energy, lattice constant, density of states, and charge density difference of the compounds before and after doping were calculated. Then, surface adsorption models of the ZrCo and Zr0.8Ti0.2Co alloys were established with the assistance of a conventional model. The resulting adsorption energy values of the clean surface and the surface adsorption energy values in the presence of CO impurity gases manifested that the Ti element-doped Zr0.8Ti0.2Co alloy was more susceptible to CO gas poisoning compared to ZrCo, which was consistent with the existing experimental results. In addition, by analyzing the conventional model, the electrons from the doped atoms overlapped with the surrounding electrons of C atoms, the phenomenon of orbital hybridization occurred, and the interactions increased. Consequently, Ti doping was not conducive to ZrCo to improve the ability to resist CO poisoning. The research results of this paper have laid a good foundation for the study of the effect of Ti doping on the antitoxicity performance.

Measurement of NO<sub><i>x</i></sub> concentration at ppb level in high-purity gases based on chemiluminescence method

High-purity gases are widely used in semiconductor device manufacturing and fuel cell industries. However, the impurities have a significant influence on the processing accuracy directly. Thus, it is particularly necessary to carry out the concentration diagnosis of key trace impurity gases. In this work, an integrated system for the simultaneous detection of trace NO/NO<sub><i>x</i></sub> is designed based on the chemiluminescence spectrum theory and the catalytic conversion mechanism of nitrogen oxides. The test experiments reveal that the measurement system has the advantages of high linearity (<i>R</i><sup>2</sup> = 0.99967), high sensitivity, low detection limit (~25 ppt), and easy operation. Subsequently, the measurement method for NO<sub><i>x</i></sub> with different high-purity gases are established considering the quenching effects of different background gases on fluorescence and phosphorescent. The detection system is then used to measure the ppb-level NO<sub><i>x</i></sub> impurities in four commonly used high-purity gases (Ar, O<sub>2</sub>, CO<sub>2</sub>, N<sub>2</sub>) in the laboratory. The results show that the NO impurity in CO<sub>2</sub> gas is the highest, approximately 9 ppb,but relatively low, 0–4 ppb, in the other high-purity gases. The NO<sub>2</sub> impurities in all four high-purity gases are very low (< 6 ppb). Finally, the NO<sub><i>x</i></sub> impurity content values in high-purity gases are evaluated and analyzed based on the gas preparation and purification approach. The aim of the work is to provide a reliable diagnostic approach and data basis of the impurity composition for the fuel cell, semiconductor and other cutting-edge technological fields.

Evaluation of functional layers thinning of high temperature polymer electrolyte membrane fuel cells after long term operation.

The operation related degradation processes of high temperature polymer electrolyte membrane fuel cell operated with hydrogen-rich reformate gas are studied. CO impurities from the reformate gas are strongly adsorbed by the catalyst surface, leading to poisoning and thus, reduction of the overall performance of the cell. Most of the studies are performed in a laboratory set-up by applying accelerated stress tests. In the present work, a high temperature polymer electrolyte membrane fuel cell is operated in a realistic configuration for 12 000 h (500 days). The fuel cell contains as electrocatalyst Pt in the cathode and a Pt-Ru alloy in the anode. The study of the degradation occurring in the functional layers, i.e. in different regions of cathode, anode and membrane layer, is carried out by scanning electron microscopy, (scanning) transmission electron microscopy and energy dispersive X-ray spectroscopy. We observed a thinning of the functional layers and a redistribution of catalyst material. The thinning of the cathode side is larger compared to the anode side due to harsher operation conditions likely causing a degradation of the support material via C corrosion and/or due to a degradation of the catalyst via oxidation of Pt and Ru. A thinning of the membrane caused by oxidation agents is also detected. Moreover, during operation, catalyst material is dissolved at the cathode side and redistributed. Our results will help to design and develop fuel cells with higher performance.

CO-Tolerant PEMFC Anodes Enabled by Synergistic Catalysis between Iridium Single-Atom Sites and Nanoparticles.

Proton-exchange membrane fuel cells (PEMFCs) are limited by their extreme sensitivity to trace-level CO impurities, thus setting a strict requirement for H2 purity and excluding the possibility to directly use cheap crude hydrogen as fuel. Herein, we report a proof-of-concept study, in which a novel catalyst comprising both Ir particles and Ir single-atom sites (IrNP @IrSA -N-C) addresses the CO poisoning issue. The Ir single-atom sites are found not only to be good CO oxidizing sites, but also excel in scavenging the CO molecules adsorbed on Ir particles in close proximity, thereby enabling the Ir particles to reserve partial active sites towards H2 oxidation. The interplay between Ir nanoparticles and Ir single-atom centers confers the catalyst with both excellent H2 oxidation activity (1.19 W cm-2 ) and excellent CO electro-oxidation activity (85 mW cm-2 ) in PEMFCs; the catalyst also tolerates CO in H2 /CO mixture gas at a level that is two times better than that of the current best PtRu/C catalyst.

CO‐Tolerant PEMFC Anodes Enabled by Synergistic Catalysis between Iridium Single‐Atom Sites and Nanoparticles

AbstractProton‐exchange membrane fuel cells (PEMFCs) are limited by their extreme sensitivity to trace‐level CO impurities, thus setting a strict requirement for H2 purity and excluding the possibility to directly use cheap crude hydrogen as fuel. Herein, we report a proof‐of‐concept study, in which a novel catalyst comprising both Ir particles and Ir single‐atom sites (IrNP@IrSA‐N‐C) addresses the CO poisoning issue. The Ir single‐atom sites are found not only to be good CO oxidizing sites, but also excel in scavenging the CO molecules adsorbed on Ir particles in close proximity, thereby enabling the Ir particles to reserve partial active sites towards H2 oxidation. The interplay between Ir nanoparticles and Ir single‐atom centers confers the catalyst with both excellent H2 oxidation activity (1.19 W cm−2) and excellent CO electro‐oxidation activity (85 mW cm−2) in PEMFCs; the catalyst also tolerates CO in H2/CO mixture gas at a level that is two times better than that of the current best PtRu/C catalyst.