Hydrogen production from the electrooxidation of methanol and potassium formate in alkaline media on carbon supported Rh and Pd nanoparticles

Article abstract of DOI:10.1016/j.ica.2017.05.055

Small organic molecules such as alcohols and formate salts can be readily transformed into hydrogen and carbon dioxide through electrochemical reforming at low energy cost. In this article methanol and potassium formate are studied for hydrogen production in alkaline anion exchange membrane electroreformers using two anode electrocatalysts, nanoparticle Pd and Rh supported on carbon (5 wt%). Firstly, we report a study of the electrochemical activity of both catalysts in electrochemical test cells at 80 °C. Formate oxidation kinetics are found to be fast on both catalysts. Rh/C shows the best performance for methanol electrooxidation with an onset potential 200 mV lower than Pd/C and a specific activity almost double reaching the value of 2600 A g^?1_Rh. The energy cost and conversion efficiency for hydrogen production was determined in complete electrochemical reforming cells at 80 °C using both anode catalysts. The energy costs are low for both substrates (<14 KWh kg^?1_H2) with Pd/C producing hydrogen from potassium formate at an energy cost of 5 KWh kg^?1_H2. Considering both the energy consumption and conversion efficiency (substrate to hydrogen), it is shown that the Rh/C catalyst performs best with methanol as substrate.

Full text of DOI:10.1016/j.ica.2017.05.055

Accepted Manuscript
Research paper
Hydrogen production from the electrooxidation of methanol and potassium for-
mate in alkaline media on carbon supported Rh and Pd nanoparticles
M.V. Pagliaro, M. Bellini, J. Filippi, M.G. Folliero, A. Marchionni, H.A. Miller,
W. Oberhauser, F. Vizza
PII:
S0020-1693(17)30527-3
http://dx.doi.org/10.1016/j.ica.2017.05.055
ICA 17625
DOI:
Reference:
Inorganica Chimica Acta
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Revised Date:
Accepted Date:
5 April 2017
22 May 2017
25 May 2017
Please cite this article as: M.V. Pagliaro, M. Bellini, J. Filippi, M.G. Folliero, A. Marchionni, H.A. Miller, W.
Oberhauser, F. Vizza, Hydrogen production from the electrooxidation of methanol and potassium formate in alkaline
media on carbon supported Rh and Pd nanoparticles, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/
10.1016/j.ica.2017.05.055
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Hydrogen production from the electrooxidation of methanol and potassium formate in
alkaline media on carbon supported Rh and Pd nanoparticles
M. V. Pagliaro,1,2 M. Bellini,1 J. Filippi,1 M. G. Folliero,1,2 A. Marchionni,1 H. A. Miller,1* W.
Oberhauser1 and F. Vizza1*
1CNR-ICCOM, via Madonna del Piano 10, 50019, Sesto Fiorentino (FI), Italy
2Università di Siena, Dipartimento di Biotecnologie, Chimica e Farmacia, via Aldo Moro 2, Siena
53100, Italy.
Email: francesco.vizza@ccom.cnr.it; hamish.miller@iccom.cnr.it
Abstract
Small organic molecules such as alcohols and formate salts can be readily transformed into
hydrogen and carbon dioxide through electrochemical reforming at low energy cost. In this article
methanol and potassium formate are studied for hydrogen production in alkaline anion exchange
membrane electroreformers using two anode electrocatalysts, nanoparticle Pd and Rh supported on
carbon (5 wt%). Firstly, we report a study of the electrochemical activity of both catalysts in
electrochemical test cells at 80 °C. Formate oxidation kinetics are found to be fast on both catalysts.
Rh/C shows the best performance for methanol electrooxidation with an onset potential 200 mV
lower than Pd/C and a specific activity almost double reaching the value of 2600 A g-1Rh. The
energy cost and conversion efficiency for hydrogen production was determined in complete
electrochemical reforming cells at 80 °C using both anode catalysts. The energy costs are low for
both substrates (< 14 KWh Kg-1H2) with Pd/C producing hydrogen from potassium formate at an
energy cost of 5 KWh Kg-1H2. Considering both the energy consumption and conversion efficiency
(substrate to hydrogen), it is shown that the Rh/C catalyst performs best with methanol as substrate.

1. 1. Introduction
One of the most important challenges for our society is to build a sustainable world economy
based on the use of clean and renewable energy. Hydrogen, thanks to its high specific energy
density and clean combustion to water, is an attractive alternative to our current dependence on
fossil fuels. Although hydrogen is the most abundant element in nature, it mostly exists combined
with other elements, so it must be produced using a primary source of energy.[1],[2] Irrespective of
how hydrogen is produced, these processes are endothermic and require a large amount of energy,
either provided as heat as in steam reforming or through electrochemical or photochemical
processes activated with suitable catalysts. [3]–[5] At present hydrogen is principally produced by
the steam reforming of hydrocarbons at high temperatures (700-1200 °C) with CO and CO2 as
waste products.[6]
Since the 1960s, hydrogen production by the dehydrogenation of formic acid or methanol,
through homogeneous or heterogeneous catalysis, has been widely investigated.[7] Different types
of catalysts have been developed, ranging from noble metals (iridium, palladium, platinum,
rhodium and ruthenium) to molybdenum and ruthenium complexes with monodentate phosphines
as ligands.[8], [9] These materials decompose formic acid to H2 and CO2, although in some cases
carbon monoxide (and water) is also formed through a side reaction. The presence of CO in the
product gas stream is problematic as small quantities can quickly poison fuel cell electrocatalysts.
[10]
Another method to produce hydrogen is through electrolysis; electrochemical routes are
particularly appealing in terms of sustainability, in fact using appropriate substrates, it is possible to
convert electrical energy directly into pure molecular hydrogen. [11]–[15] The most established
technology is water electrolysis, although this method has a high energy cost due to the high cell
voltages required to produce hydrogen (> 1.23 V RHE at room temperature).
Methanol and formic acid have been widely studied as potential fuels for Direct Fuel Cells
(DFCs) thanks to their low molecular weight, ease of transport and storage and high energy
densities. [16]–[18] There are only a very few works that report their use in electrolysis cells to
produce hydrogen through a technology known as electrochemical reforming.[19]–[21]
Electrochemical reforming produces hydrogen as low energy cost by replacing the anodic oxygen
evolution reaction with the oxidation of a sacrificial substrate (e.g. alcohol or formate). For
example, the electrical energy input for an electroreformer fed with ethanol consumes less than half
of that required to produce the same amount of hydrogen from water splitting.[11] In comparison to
catalytic reforming technologies where the product gas stream contains a mixture of H2 and CO2,

electrochemical reforming in alkaline media produces pure hydrogen at the cathode . This is
because the anode and cathode are separated by a membrane. Additionally, the CO2 produced from
the oxidation of the anolyte is transformed into carbonate by reaction with the strong base in the
electrolyte and hence cannot migrate to the cathode and mix with the hydrogen gas stream.
As alternative to formic acid, which is corrosive and dangerous to human health, formate salts
are less toxic, less volatile, and can be easily stored and transported. Moreover, as shown in a
number of recent reports, Direct Formate Fuel Cells (DFFCs) produce high power densities as the
kinetics of the formate oxidation reaction is very fast in alkaline media.[22]–[24]
In this article, we investigate the electrooxidation of methanol and formate in electrochemical
cells as well as in complete electrolysis cells at 80 °C. As electrocatalyst we study two carbon
supported nanoparticle based catalysts, Pd/C and Rh/C, each with a 5 wt% metal loading. This
study evaluates the energy efficiency and stability of the electrolysis process with methanol and
formate, using these two electrocatalysts. We demonstrate that with the use of these anode
electrocatalysts, it is possible to obtain high purity hydrogen (CO2 free) at low energy cost. An
energy analysis shows that Rh outperforms Pd both in terms of energy cost as well as conversion
efficiency. Considering the yield of hydrogen, methanol is preferable as substrate as more hydrogen
is obtained per molecule compared to formate while the energy cost remains the same.
2. 2. Experimental
2.1 Materials and methods
Carbon black (Vulcan XC-72) was purchased from Cabot Corp., USA. The alkaline anion
exchange membrane used was A201 obtained from Tokuyama Corp. (Japan). All metal salts and
reagents were purchased from Aldrich and used without further purification. All the solutions were
freshly prepared with doubly distilled deionized water. All materials preparation, except as stated
otherwise, were routinely performed under nitrogen atmosphere using standard airless technique.
The active metal surface area and average nanoparticle size were determined by a CO
chemisorption method, adapted to carbon supported materials, at 35°C by the use of an ASAP
2020C Instrument (Micromeritics Corp.). Before the measurements, the samples were treated at 120
°C with H2 for 12 hours.
The electrochemical measurements were carried out using a Parstat 2273 potentiostat-
galvanostat (Princeton Applied Research) equipped with a Model 616 Rotating Disk electrode
(PAR-Ametek). A 5 mm (A = 0.1963 cm2) teflon potted glassy-carbon disk electrode tip (PINETM)
was used as substrate for the deposition of the catalyst ink. Before the deposition, the glassy-carbon

surface was polished with different CT diamond suspensions that had progressively smaller particle
size (1 µm, 0.25 µm, 0.1 µm) and finally washed with distilled water. The catalyst ink consisted of
Rh/C or Pd/C (14 mg) and water (1.2 g). The resulting suspension was sonicated for 1 h with a
FALC sonic bath to reach a uniform suspension. The catalyst film was prepared by dispersing 8 µL
of the catalyst ink on the glassy-carbon electrode. The exact amount of ink deposited was
determined using an analytical balance. The final metal loading on the electrode is between 5 and 6
µg. Each electrode was dried for 30 min before the addition of 2.5 µL of a Nafion solution (0.5%)
and finally it was mounted on the rotating disk electrode shaft and immersed into the electrolyte
solution. The reference electrode was a commercial Ag/AgCl/KCl (1M). The counter electrode was
a platinum gauze enclosed in a glass tube with porous bottom. All the potentials reported are versus
the reversible hydrogen electrode (RHE). The electrochemical experiments were conducted at 80°C.
The CV experiments were registered in either 2M aqueous KOH or 2M KOH + 2M methanol or
potassium formate. All the solutions were prepared with Millipore water (18MΩcm) provided by a
milli-Q labo apparatus (Nihon Millipore Ltd.). Solutions were first treated by bubbling high-purity
N2 before measurements.
The MEAs (membrane electrode assemblies) were composed of a nickel foam support
coated with a Rh/C or Pd/C catalyst as anode, a commercial Tokuyama A-201 anion-exchange
membrane, and a commercial 40 wt% Pt/C (Aldrich) catalyst supported on carbon cloth as cathode.
The anode ink was prepared by mixing Rh/C or Pd/C (C=Vulcan XC-72) with a 5% aqueous
suspension of PTFE to form a think catalyst paste which is spread onto a 5 cm2 Ni-foam support
(Heze Tianyu Technology Development Co, China) in order to obtain a catalyst coated electrode
with a metal loading of 1 mg cm-2. The cathodic ink was prepared in a 5 mL high density
polyethylene vial, mixing 200 mg of the commercial Pt (40 wt.%)/C in 450 mg of distilled water,
790 mg of 1-propanol and 1.56 g of the ionomer Nafion® (5 wt.% in 2-propanol). The mixture was
suspended with three pulses of ultrasound, 20 W power at the frequency of 20 kHz (Bandelin Sonor
pulse UW 2200 SERIES). Finally this paste was spread onto a carbon cloth W1S1005 (CeTech Co.
Ltd.) gas diffusion layer, with a Meyer rod (n°150) obtaining a 0.4 mg cm-2 Pt loading.
The active electroreformer cell was purchased from Scribner-Associates (USA). The MEAs
were assembled by mechanically pressing together the anode, cathode and membrane within the cell
hardware. The cell temperature was regulated at 80 °C using a Scribner 805e fuel cell station. The
aqueous fuel solution (2M KOH + 2M methanol or potassium formate) was delivered to the anode
at 1 mL min-1. Voltage scans and galvanostatic curves were determined using an ARBIN BT-2000
5A-4 channels instrument. Polarization experiments were recorded by applying a linear voltage
ramp with a 10 mV s-1 scan rate between 0.2 to 0.8V. Chronopotentiometry experiments were

performed applying a constant electrolysis current of 125mA until the cell voltage reached the value
of 0.65 V. The fuel solutions after each experiment were quantitatively and qualitatively analyzed
by 13C{1H} NMR spectroscopy and HPLC. A UFLC Shimadzu Chromatograph equipped with
refraction index detector (RID) was used; the column is a GRACE- Alltech OA-1000 Organic
Acids (300mm x 6.5 mm), thermostated at 65°C. The eluent is 0.01 N H2SO4; and the eluent flow is
0.4 mL min-1. NMR spectra were acquired with a with a Bruker Avance DRX 400 spectrometer.
Chemical shifts (δ) are reported in ppm relative to TMS (1H and 13C NMR spectra). Deuterated
solvents (Sigma-Aldrich) used for NMR measurements were dried with activated molecular sieves;
1,4-dioxane was used as internal standard for product quantification.
2.2 Synthesis of electrocatalysts
The detailed synthesis of Rh/C (Rh =5 wt%) and Pd/C (Pd =5 wt%) anode electrocatalysts has been
already reported in our previous works[25], [26]. Briefly, as follows:
Rh/C: Vulcan XC-72 (3.8 g) was suspended in 640 mL of ethylene glycol and sonicated for 80
min. Then the suspension was mechanically stirred (400 rpm) for 1 h under a N2 atmosphere. A
solution of 740 mg of RhCl3•6H2O in water (160 mL) was added dropwise to the suspension under
stirring. Subsequently an alkaline solution of 15.8 g of NaOH in water (80 mL) and ethylene glycol
(200 mL) was introduced to the reactor and the resulting mixture was heated at 120 °C for 3 h.
After cooling to room temperature the resulting solid product was collected by filtration and washed
with water to neutral pH and lastly dried in vacuum oven at 40 °C. Yield of Rh/C: 80%.
Pd/C: Vulcan XC-72 (4.5 g) was suspended in 250 mL ethylene glycol and sonicated for 20 min.
Then a solution of 50 mL of H2O, 50 mL of ethylene glycol and 6 mL of HCl (37%,) with dissolved
445 mg of PdCl2 were added drop by drop to the resulting solution under stirring in a N2 stream. An
alkaline solution of 5 g of NaOH in H2O (10 mL) and ethylene glycol (35 mL) was introduced into
the reactor which then was heated at 125°C for 3 h. After cooling to room temperature the resulting
solid product was collected by filtration and washed with water to neutral pH and lastly dried in
vacuum oven at 40 °C. Yield of Pd/C: 94 %.

3. 3. Results and discussion
3.1.Chemisorption measurements
The active surface area and the mean nanoparticle size for both the Rh/C and Pd/C electrocatalysts
were calculated by a CO chemisorption method; the respective values are reported in Table 1.
Table 1: Chemisorption data.
Electrocatalyst
Rh/C
Mean Nanoparticle Size (nm)
Metal Specific Surface Area (m2 g-1
)
Metal
5
9
76
52
Pd/C
These values are consistent with what has been found by the use of other physical and
electrochemical characterization techniques in previous reports. For the Rh/C catalyst, an average
particle size was estimated from a statistical count using TEM images and gave a value of 2.2 nm.
CO stripping voltammetry gave a value for the ECSA of 75 m2 g-1Rh.[26] A recent TEM
investigation of the Pd/C catalyst showed a NP distribution of 2-10 nm.[25]
3.2.Half-cell testing
The electrochemical activity of Pd/C and Rh/C was investigated using cyclic voltammetry (CV)
studies in electrochemical three electrode test cells. All the experiments were performed in N2-
saturated aqueous solutions, and using a metal loading on the glassy carbon substrate of 25-35 µg
cm-2. Firstly, we studied the electrochemical behavior of both catalysts (without fuel) in 2 M KOH
at 80°C (Fig. 1). The potentials reported in the cyclic voltammetry curves reported versus RHE are
calculated according to the Ag|AgCl|KClsat electrode temperature dependence as described in the
supplementary of our previous work.[26]
The different transitions observed in each CV can be assigned by comparison with literature
data.[25], [26] In the case of Pd/C, starting from the low potential region, on the anodic sweep we
first see a large broad peak (A’) with a shoulder attributable to the oxidative desorption of
hydrogen. Subsequently there is a small peak (A’’) at 0.4 V which can be assigned to the formation
of Pd(I) hydroxide species (Pd-OH).[27] This is followed by the formation of an oxide layer (A’’’)
on the palladium surface that is associated with a gentle increase in the anodic current density. On
the reverse cathodic scan, a well-defined peak (C’) at 0.85 V is attributed to the reduction of Pd
surface oxides species. At potentials between 0.1 and 0.2 V there is a large cathodic current (C’’)

associated to the adsorption of hydrogen on the Pd surface and then hydrogen evolution. [22], [25],
[28].
Fig. 1 CVs of Rh/C (ꢀ) and Pd/C (•) in N2 saturated 2M KOH at 80°C and a scan rate of 50 mV s-1.
The CV of Rh/C in KOH 2M at 80 °C corresponds to data recently reported in the literature.
[25], [26] The anodic peaks can be assigned to hydrogen desorption (A’ at 0.1 V), the formation of
RhxOHy (A’’ at 0.3 V) and RhxOy (A’’’ at 0.6 V). In the reverse scan there are peaks for the
reduction of the oxide layer (0.35 V) and for hydrogen adsorption (0.05 V).[29]–[31]
We also studied the electrochemical oxidation activity by cyclic voltammetry of both
catalysts in 2M KOH + 2M potassium formate (Figure 2, A and B) and 2M KOH + 2M methanol
(Figure 2, C and D) in the potential range of 0-1.20 V vs. RHE at the temperature of 80 °C and at a
scan rate 50 mV s-1. Fig. 2A shows formate oxidation activity of Pd/C. The onset potential is low at
about 0.2 V, and there is a specific activity of 2.1 mA µg-1Pd, for the forward going peak (important
electrochemical data is also reported in Table 2). We have recently reported a cyclic voltammetry

study of a Pd/C electrocatalyst (Pd = 20 wt%) with potassium formate in alkaline media at room
temperature.[22] The peak current density for potassium formate oxidation was at least three times
lower compared to this work even with a much higher Pd loading. This confirms the positive effect
of increased temperature on oxidation kinetics of alcohols in alkaline media. In the case of methanol
Fig. 2 C, Pd/C has a higher onset potential representing the more difficult nature of methanol
oxidation. In both CVs (A and C) the reverse scan shows an anodic peak corresponding to fresh
oxidation of the fuel after reduction of the surface Pd oxides.[32] Regarding the electrochemical
activity of rhodium, with both fuels the onset potentials are lower than Pd (see data reported in
Table 1). The oxidation peak on the forward scan is much higher for methanol than formate
reaching a specific current value of 2.6 mA µg-1Rh (Fig. 2 D).
Fig. 2 CVs of Pd/C in 2M KOH + 2M Potassium Formate (A) and 2M KOH + 2M Methanol (C),
and Rh/C in 2M KOH + 2M Potassium Formate (B) and 2M KOH + 2M Methanol (D). Scan rate of
50 mV s-1.

Table 2 Relevant electrochemical parameters of CVs of Pd/C and Rh/C with Potassium Formate
and Methanol at 80°C and a scan rate of 50 mV s-1. a Current density normalized to metal loading
Pd/C
Rh/C
a
a
Fuel
Eonset
Eforward peak
Jpeak
Eonset
Eforward peak
Jpeak
(V vs. RHE) (V vs. RHE) (mA µg-1
)
(V vs. RHE) (V vs. RHE) (mA µg-1
)
Pd
Rh
Formate
0.20
0.62
0.81
0.90
2.1
1.5
0.30
0.42
0.52
0.65
0.9
2.6
Methanol
3.3.Electrolysis cell testing
Nickel foam (4 cm2) coated with either of the Rh/C or Pd/C catalyst inks was used as anode
electrode (1 mgmetal cm2) in the electrolyzer equipped with an anion exchange membrane
(Tokuyama A201) and a Pt/C on carbon cloth cathode (0.4 mgPt cm-2). The fuel, fed to the anode,
was an aqueous solution (30 mL) of 2M KOH and 2M potassium formate or 2M KOH and 2M
methanol.
The electrolysis cell performance were evaluated using both potentiodynamic scans and
galvanostatic experiments at 80°C. The experiments were repeated three times, using the same cell
and only changing the fuel with a fresh solution. Every cycle of experiments consisted of a voltage
scan, undertaken in the potential range from 0.2 to 0.8V at 10 mV s-1, followed by a galvanostatic
experiment (at a costant electrolysis current of 125 mA). The cell potential was monitored and the
experiment was stopped when it reached 0.65 V. The first cycle of the voltage scans are reported in
Fig. 3. The Rh/C cell reached a higher maximum current density with both methanol and potassium
formate compared to Pd/C. The values of peak current density are reported in
Table 3. The electrochemical activity of both Pd/C and Rh/C was stable over all the three cycles
confirming the stability of the anode materials during electrooxidation.

Fig. 3 First cycle of the potentiodynamic experiments of Pd/C with 2M KOH + 2M Formate (A)
and 2M KOH + 2M Methanol (C), and of Rh/C 2M KOH + 2M Formate (B) and 2M KOH + 2M
Methanol (D). Scan rate of 10 mV s-1. Cell temperature 80 °C.
Table 3 Relevant electrochemical parameters of the cell at 80°C using Pd/C or Rh/C as anode and
2M KOH + 2M Formate or 2M KOH + 2M Methanol as fuel.
Pd/C
Rh/C
Energy
Energy
Jmax
Conversion
H2 produced
(Nm3 m-2)
consumption
(KWh Kg-1H2)
Jmax
(mA cm-2)
Conversion
H2 produced
(Nm3 m-2)
consumption
(KWh Kg-1H2)
Fuel
(mA cm-2)
(%) [mmol]
(%)[mmol]
Formate
460
580
75 [45]
38 [23]
2.5
3.8
5
510
780
79 [47]
51 [31]
2.6
4.8
8
Methanol
14
12

Fig. 4 First cycle of the galvanostatic experiments of Pd/C with 2M KOH + 2M Potassium Formate
(A) and 2M KOH + 2M Methanol (C), and of Rh/C 2M KOH + 2M Potassium Formate (B) and 2M
KOH + 2M Methanol (D). Constant current of 125 mA. Cell temperature 80 °C.
The galvanostatic experiments, shown in Fig. 4, were performed to determine the energy
efficiency and conversion efficiency of the system for hydrogen production. For each cycle, 30 mL
of fresh fuel was provided to the anode compartment of the cell. A constant current (125 mA) was
set to the cell and the change in potential was recorded over time until it reached a value of 0.65 V.
The same experiment was repeated three times changing only the fuel solution. The reproducibility
of the experiment during time confirmed the stability of the catalysts (see Figures S1 and S2 in the
Supporting information). With potassium formate, the only possible product that can be formed is
carbonate; in the case of methanol, from 13C{1H}NMR analysis of the fuel exhausts, we found that
with Pd/C 100% of CO32- was obtained while Rh/C oxidizes methanol to 85% of CO32- and 15% of
formate. On the basis of this selectivity, and the number of moles of electrons exchanged during the
experiment, we have calculated the conversion % of the fuel and the quantity of hydrogen produced
(see
Table 3). The energy consumption was also calculated from the integration of the
instantaneous charging power over duration time of the experiment. All the obtained values,
reported in
Table 3, are under 14 KWh Kg-1H2. Pd/C presents the best performance with formate as fuel
showing a value of 5 KWh Kg-1H2. The Faradic efficiency, defined as the ratio between the

discharge capacity and the theoretical discharge capacity, has been calculated from galvanostatic
experiments. In the case of formate oxidation to carbonate, it is equal to 74% for Pd/C and 78% for
Rh/C; and in the case of methanol oxidation values of 38% for Pd/C and 48% for Rh/C were
obtained. The faradaic efficiencies obtained for methanol were lower than formate. We believe this
was mostly due to loss of methanol through crossover from the anode solution and evaporation at
the cathode as no methanol was found in the fuel solution after the experiments. From the
13C{1H}NMR analysis of the fuel exhausts we have demonstrated that Pd/C and Rh/C have
different selectivity for methanol oxidation: Pd/C leads to 100% of carbonate, and Rh/C to 85% of
carbonate and 15% of formate. The complete oxidation of methanol to CO32- involves six electrons.
For both electrocatalysts, there are two possible pathways of electrooxidation of methanol, firstly
through the formation of formate (scheme 1 path a and e) and its direct oxidation to carbonate, and
an indirect pathway through the formation of poisoning species (COad) and finally of carbonate
(path b and d).[16] In our study, given the fast kinetics with which formate is oxidized to carbonate
and the presence of formate as intermediate, we can assume that the most likely path is the one
(path a) that avoids poisoning intermediates. This is in agreement with what is reported in the
literature, indeed formate has been identified as an active intermediate for the direct oxidation of
methanol on Pt electrodes. [33]
Scheme 1: Methanol oxidation process in alkaline medium.[16]
Conclusions
In this paper, we report a study of the electrooxidation performance of Pd/C and Rh/C
catalysts, in alkaline media at 80 °C. The two fuels studied were potassium formate and methanol.
The electrochemical measurements show for both metals low onset potentials, and high specific
current densities. In particular, Pd/C with formate, exhibits an onset of 200 mV and a specific
activity of 2100 A g-1Pd; while Rh/C has an excellent activity for methanol oxidation, showing an

onset potential 200 mV lower than Pd/C and a specific activity almost double reaching the value of
2600 A g-1
.
Rh
In complete electrolysis cells, high current densities for hydrogen production are obtained at
low cell potentials. Indeed, the energy costs are very low for both substrates (< 14 KWh Kg-1H2).
Pd/C with formate shows 5 KWh Kg-1H2. Taking into account both the energy consumption and
conversion efficiency then we can conclude that the Rh/C catalyst performs best with methanol as
substrate.
In summary, we report for the first time a complete study of alkaline alcohol electrolyzers fed with
methanol and formate. We have evaluated the energy consumption for the production of CO2-free
hydrogen, demonstrating the ability of the Rh/C and Pd/C anode catalysts to perform the complete
oxidation of methanol, without being subject to CO poisoning, confirmed by their stability over
continued testing.
This technology is an important example of novel strategies for the conversion of waste
biomass into valuable biofuels e.g. hydrogen. Today, in fact, there is a need to search for more
sustainable fuels to develop a carbon-neutral energy economy, and hydrogen is an excellent
candidate for becoming a next-generation bio-fuel.[34] Technologies such as electroreforming can
be easily integrated into a future energy system not based upon oil, which are based upon the
exploitation of local sources of biomass.
ACKNOWLEDGMENTS
The Ente Cassa di Risparmio di Firenze (project EnergyLab).
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Highlights:
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Rh and Pd nanoparticles supported on carbon were studied for the electrooxidation of
formate and methanol
The electrooxidation of methanol and formate to hydrogen was investigated in complete
electrolysis cells
The energy consumption for the production of CO2-free hydrogen was determined.