H2O2 out of a new fuel-cell?

[Saugi]

A few years ago, the japans discovered a new way to produce H2O2 up to 3,5% in a new invented fuel-cell.

I wonder, if this method has established today and if we can make this work at home - which would be very interesting. Is someone here who has more informations about that?

This is the article about the new fuel-cell:

A new fuel-cell concept for the catalytic production of hydrogen peroxide
08 Aug 2003 - Hydrogen peroxide is an important industrial reagent, which is used in such processes as the environmentally friendly bleaching of paper and wastewater treatment. Current industrial methods for the bulk production of H2O2 are expensive, both in terms of energy and cost. A new method developed by Japanese researchers could form the basis of a new, substantially more economical process.

Ichiro Yamanaka's team has been working on the catalytic conversion of hydrogen and oxygen into hydrogen peroxide. A mixture of hydrogen and oxygen is highly explosive. Yamanaka and his co-workers thus chose a method that guarantees a controlled reaction, even though the two volatile reactants never come into direct contact: electrocatalytic conversion in a fuel cell. The special advantage of this concept is that the energy released in the reaction can be captured in the form of an electric current. The researchers have now further improved their original fuel cell concept.

The secret of their success is a three-phase interface within the cathode, the negative electrode. Rather than introducing oxygen in an electrolyte solution, as was done previously, a stream of oxygen gas is introduced directly onto the solid, but porous, cathode. The other side of the cathode contains a dilute sodium hydroxide solution as an electrolyte, which also enters the pores. This allows for higher oxygen concentration on the inner electrode surface, allowing in turn for a higher conversion. Hydrogen gas is directed in a similar way onto the equally porous anode.

A further crucial improvement lies in the enclosure of the electrolyte solution within cathode and anode areas by a semipermeable membrane. This solves another problem that plagued the previous version of the fuel cell; the hydrogen peroxide formed at the cathode no longer has access to the anode, where it would decompose to form water. Last but not least, the efficacy of the catalytic graphite electrodes was increased by the inclusion of various additives.

Even when air is used in place of pure -- expensive -- oxygen, the output of the fuel cell is high enough. This renders the concept an economically interesting alternative for the bulk production of hydrogen peroxide.

[megalomania]

A very interesting find. I did a little checking on professor Yamanaka, who is an associate professor in the Department of Applied Chemistry at Tokyo Institute of Technology. Based on his publications, all of his research is electrochemical in nature, with particular attention on hydrogen production and fuel cell technology, as well as oxidations.

He has four published journal articles about electrochemical hydrogen peroxide production, at least with English titles that I could read, only one of which I was able to obtain, the paper that Saugi’s news article referred to. The latest two articles only came out last year, one in Chemical Letters, which is a Japanese publication I do not have access to either electronically, or in the stacks, and the other has a Japanese title I can not read.

Here is the abstract from professor Yamanaka’s latest publication in Chemical Letters 35, 12, 1330-1331, (2006).


Electrocatalysis of Heat-treated Mn–Porphyrin/Carbon Cathode for Synthesis of H2O2 Acid Solutions by H2/O2 Fuel Cell Method
Ichiro Yamanaka1), Takeshi Onizawa1), Hirobumi Suzuki1), Noriko Hanaizumi1) and Kiyoshi Otsuka1)
1) Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology
(Received August 21, 2006)

Mn–porphyrin supported on active carbon, which was activated by heat-treatment in Ar, electrochemically catalyzed reduction of O2 to H2O2 by the H2/O2 fuel cell method. The electrocatalytic activities were strongly dependent on the heat-treatment temperatures. The maximum H2O2 concentration of 3.5 wt % with 47% current efficiency was obtained for the catalyst treated at 450 °C, and a TON (Mn) for the H2O2 formation was over 1000 h−1


On closer examination of the news article that Saugi posted shows a bit of a percentage discrepancy. The news article says the process can achieve a hydrogen peroxide concentration of 3.5%, but the journal article says the maximum concentration they obtained was 7% using an improved setup. Using pure oxygen they reached a concentration of 7% in only 2 hours at a current efficiency of 94%. Using air, instead of the much more expensive oxygen, they reached a concentration of 6.5% in 3 hours at a current efficiency of 88%.

The setup does not strike me as something very OTC, but if one were to buy the electrodes and build the cell they could manufacture their own hydrogen peroxide in a very compact and energy efficient setup. I imagine this would be of particular interest to model rocket enthusiasts who consume rather large quantities of hydrogen peroxide, and who have their own distillation or concentration apparatus.

The only raw materials consumed in the reaction are air and electricity, the most plentiful OTC substances besides dirt and water. Sodium hydroxide is used as an electrolyte, but I am not sure it is consumed.

Since I doubt my describing the Cliff’s notes version of the setup would do it justice, I’ll just reproduce that snippet. There are no actual experimental details per se, just a description of the setup. I don’t know much about applied electrochemistry, but I gather these techniques are quite well known to the authors, so they feel no need to describe the experimental procedures. I am trying to learn about electrochemistry in greater detail this summer, but I am having trouble finding that ultimate book where they tell you HOW to do the reactions. I found plenty of analytical fluff and theoretical mumbo jumbo.

The article from Angewandte Chemie International Edition (the thank god they finally publish in English edition), 42, 3653-3655 (2003)

Direct and Continuous Production of Hydrogen Peroxide with 93% Selectivity Using a Fuel-Cell System
Ichiro Yamanaka,* Takeshi Onizawa, Sakae Takenaka, and Kiyoshi Otsuka

We propose a new concept and a new fuel-cell setup for the synthesis of H2O2 in order to increase the concentrations of O2 at the cathode at atmospheric pressure. Our idea is an application of a three-phase boundary (gaseous O2, aqueous electrolyte, and solid cathode) for the formation of H2O2, (Figure 1b). If a porous membrane electrode is used, a high partial pressure of O2 (101 kPa, 45 mm) can be applied directly to the active site at the three-phase boundary.[12]

Therefore, the reduction of O2 to H2O2 should be accelerated, and the successive reduction of H2O2 to H2O should be decelerated.

The porous cathode was prepared from carbon powder (vapor-grown carbon-fiber (VGCF), 13 m2 g_1, Showa-Denko Co.) and poly(tetrafluoroethylene) powder (PTFE, Daikin Co.) by the hot-press method.[13] The anode was also prepared from VGCF, PTFE, and Pt-black powders by the hot-press method. Pure O2 (20 mLmin_1) and H2 (20 mLmin_1) were supplied. The yield of H2O2 was determined by titration against KMnO4, and the current efficiency was calculated based on the two-electron reaction. The current efficiency corresponds to H2O2 selectivity based on H2.

It is well known that graphite electrodes are active for the electrolysis of O2 to H2O2 in alkaline solution.[2,3] We chose VGCF as the cathode material because it has good graphitic structure and high chemical stability. First, the one-compartment cell (system 1) was used for the direct synthesis of H2O2 over the VGCF cathode with NaOH solutions (2 molL_1) at 298 K (Figure 2a). The concentration of H2O2 increased with reaction time and showed an upper limit of 2.2 wt% at 2 h. The current density gradually decreased with reaction time and was almost constant (70 mAcm_2) at 2 h (Figure 2b). Therefore, current efficiency (H2 selectivity) decreased with reaction time from 80% at 10 min to 38% at 2 h. In other words, the H2O2 yield decelerated with reaction time.

Although the one-compartment fuel cell described above (Figure 1b) was indeed effective for the production of more concentrated H2O2 solutions, the final current efficiency of 38% was not enough. We assumed that catalytic decomposition or reduction of H2O2 over Pt-black is occurring. Therefore, the electrolyte compartment was divided into two compartments (1.18 mL each) separated by a cation
membrane (Nafion-117, DuPont) to prevent diffusion of H2O2 from the cathode to the anode sides (system 2). Cationic species can pass from one side to the other but anionic species cannot. In alkaline solution hydrogen peroxide is present as HO2_.[2, 3] Therefore, we assumed that the diffusion of HO2_ could be controlled by the Nafion membrane.

When we tested the two-compartment reactor the concentration of H2O2 increased with the reaction time and reached 4.2 wt% after 2 h with a high current efficiency of 93.7% (Figure 2a). The separation of the lectrolyte compartment was very effective for H2O2 production. In contrast to system 1, however, the current density in the system 2 decreased remarkably with reaction time (Figure 2 b), which is a serious problem. We have observed that the electrolyte volumes in the cathode and the anode smoothly increased and decreased, respectively, with charge passed. It could be estimated that six to seven molecules of H2O diffused from the anode to the cathode per each electron passed. In system 2, H2O coordinated to Na+ should be carried from the anode to the cathode. The decrease in the amount of electrolyte in the anode should cause the decrease in the current density.

To fill up the anode, the NaOH electrolyte was injected (1.5 mLh_1) with a microsyringe pump (system 3). The stability of current density was considerably improved (Figure 2b). The concentration of H2O2 smoothly increased and reached 6.0 wt% after 2 h with a high current efficiency of 93.5%(Figure 2a). The upper limit of the concentration of H2O2 was observed after 2 h, but the H2O2 yield increased linearly with reaction time. The upper limit of the H2O2 concentration was due to the increase in the volume of the H2O2 solution. That is, system 3 produced H2O2 solution at a concentration of 6 wt% continuously with high current efficiencies >90%.

To further optimize the production of H2O2 the ratedetermining step in the system 3 was studied electrochemically. The open circuit voltage of the system 3 was 0.919 V (cathode potential: _0.102 V, anode potential: _1.021 V vs Agj AgCl). The over potential of cathode was 0.550 V and that of anode was 0.230 V at 70 mAcm_2. IR drop of the electrolyte was 0.095 V (electric resistance of NaOH electrolyte: 1.35 Wcm) and that of the Nafion membrane was 0.044 V (resistance of Nafion in NaOH: 34.6 Wcm). These data suggest that the cathode reaction, the reduction of O2 to H2O2, limits the reaction rate of the system 3.

We have improved the electrocatalytic activity of the VGCF cathode by including several additives. We found that the addition of a small amount of carbon-black materials, Black Pearls 2000 (1475 m2 g_1, Cabot Co) and Valcan XC-72 (254 m2 g_1, Cabot Co.), to the VGCF cathode increased the current density and the formation rate of H2O2 by a factor of more than 1.4 with high current efficiency. We chose cathode components of VGCF (70 mg), XC72 (10 mg), and PTFE powder (7 mg) after many tests, because high activity and good reproducibility were obtained. The time course of H2O2 formation by the cell using the new cathode and anode (system 4) was shown in Figure 3. The concentration of H2O2 increased rapidly, comparable to that in system 3, and reached 7.0 wt%with 94% current efficiency at 2 h. The rate of H2O2 formation (2.0 mmolh_1cm_2) in system 4 was 1.7 times greater than that in system 3 (1.2 mmolh_1cm_2). The current density of system 4 (100 mAcm_2) was comparable to that of the electrolysis method (80–120 mAcm_2).[2,3]

In all of the experiments described pure oxygen (P(O2)=1atm) was used for the synthesis of H2O2. If we could use air (P(O2)=0.21atm), production costs could be cut tremendously. When air was used for system 4, the concentration of H2O2 increased smoothly with reaction time and reached 6.5 wt% with 88% current efficiency at 3 h. The formation rate of H2O2 (1.3 mmolh_1cm_2) and a current density (78 mAcm_2) were slightly reduced when air was used, but performance was still very good. This result suggests that the fuel-cell method (system 4) has a great advantage for the industrial production of H2O2.

In conclusion, the H2/O2 fuel-cell method showed very good performance for the selective and continuous synthesis of H2O2 because gaseous O2 could be supplied directly to the active site (the three-phase boundary) in the cathode, and the successive reduction of H2O2 over the anode could be avoided. If the apparent surface area of the electrodes of the system 4 could be increased to 1m 2 with the same performance (current density: 100 mAcm_2 (1000 Am_2) and current efficiency: 93%), aqueous alkaline solutions of 7 wt% H2O2 could be produced continuously at a rate of 8.3 Lh_1m_2.