Net Energy Balance Assessment of a Coupled Photoelectrochemical H2
Production and Hydrogenation Device
Xinyi Zhang1, Keisuke Obata1, Michael Schwarze2, Reinhard Schomäcker2, Roel van de
Krol1, Fatwa F. Abdi1
1Institute
for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-MeitnerPlatz 1, 14109 Berlin, Germany
2Technische Universität Berlin, Department of Chemistry, TC8, Straße des 17. Juni 124, 10623 Berlin,
German
*xinyi.zhang@helmholtz-berlin.de
Abstract
Photoelectrochemical (PEC) water splitting is a promising renewable energy technology to
produce green hydrogen for the future fossil-fuel-free society. Over the past decade, research
on PEC water splitting devices has achieved significant improvements in the demonstrated
solar-to-hydrogen (STH) efficiencies. The improved efficiencies have led to the development
of large-scale devices [1,2] and the coupling of hydrogen production with the synthesis of
valuable chemicals [3][4]. The co-generation approach offers a potential route towards
achieving a levelized cost of hydrogen (LCOH) that is competitive with the current market
price of hydrogen and increases the overall economic feasibility of the PEC technology.
This study evaluates the potential of co-producing hydrogen and methyl succinic acid (MSA)
by coupling the hydrogenation of itaconic acid (IA) into MSA inside a PEC water splitting
reactor. We used a PEC device that uses BiVO4 as the top absorber and a silicon solar cell as
the bottom absorber, as reported previously [1,5]. To address the feasibility of this approach,
a net energy balance assessment is conducted, and the results are compared with the
benchmark values for conventional MSA production. We follow the Techno-Economic
Assessment & Life Cycle Assessment Guidelines for CO2 Utilization (Version 1.1) which
provides a specific protocol for multi-functional PEC devices [6]. Life cycle inventory (LCI)
values from the literature and Ecoinvent database [7] are used to construct the target
scenarios in Simapro v9.2.0.
Our results show that the energy demand of our PEC device is ca. 3800 MJ/m2, and the most
energy intensive components are the photoelectrode (~70%) and the Nafion membrane (8%).
Under the base case condition (i.e., STH = 5%, device longevity = 10 years) and when H2 is the
only product, a negative net energy balance of ca. -160 MJ/m2/year is obtained. However,
with a coupled hydrogenation reaction, a zero net energy balance (i.e., energy breakeven)
can already be achieved when only 2% of the produced H2 moleculed are converted into
MSA(see red circle in Fig. 1a). Figure 1b shows the cumulative energy demand to produce one
kg of MSA under a more optimistic scenario, in which the H2-to-MSA conversion efficiency is
0.4. Under this condition, the net energy production is ca. 3500 MJ/m2/year, which translates
to a cumulative energy demand of ca. 13 MJ/kg of MSA (see red circle in Fig. 1b). This is much
lower compared to MSA produced using conventional hydrogenation methods (i.e., ~90
MJ/kg MSA), which underlines the attractiveness of the coupled PEC approach.
Finally, we analyze the potential for further improvement of the net energy balance. We
explore possibilities of replacing device components (e.g., photoelectrode, membrane) and
assess the impact to the net energy balance of the device. The result of this optimization study
will be presented, and the most effective strategy will be outlined.
Figure 1. Colormap of (a) the required H2-to-MSA conversion efficiency to achieve energy
breakeven and (b) the cumulative energy demand (MJ) to produce 1 kg of MSA when the
molar H2-to-MSA conversion efficiency is 0.4 for various STH efficiencies and device
longevities.
Keywords: water splitting, (photo)electrochemistry, net energy assessment, coupled catalysis,
hydrogenation
References
[1]
Ahmet IY, Ma Y, Jang JW, Henschel T, Stannowski B, Lopes T, Vilanova A, Mendes A, Abdi FF,
Van De Krol R. Demonstration of a 50 cm2 BiVO4 tandem photoelectrochemical-photovoltaic
water splitting device. Sustain Energy Fuels. 2019;3(9):2366–79.
[2]
Tolod KR, Hernández S, Russo N. Recent advances in the BiVO4 photocatalyst for sun-driven
water oxidation: Top-performing photoanodes and scale-up challenges. Catalysts. 2017;7(1).
[3]
Mei B, Mul G, Seger B. Beyond Water Splitting: Efficiencies of Photo-Electrochemical Devices
Producing Hydrogen and Valuable Oxidation Products. Adv Sustain Syst. 2017;1(1–2).
[4]
Luo H, Barrio J, Sunny N, Li A, Steier L, Shah N, Stephens IEL, Titirici MM. Progress and
Perspectives in Photo- and Electrochemical-Oxidation of Biomass for Sustainable Chemicals
and Hydrogen Production. Adv Energy Mater. 2021;11(43).
[5]
Abdi FF, Han L, Smets AHM, Zeman M, Dam B, Van De Krol R. Efficient solar water splitting by
enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode. Nat
Commun [Internet]. 2013;4:1–7. Available from: http://dx.doi.org/10.1038/ncomms3195
[6]
Zimmermann AW, Wang Y, Wunderlich J, Buchner GA, Schomäcker R, Müller LJ, Langhorst T,
Kätelhön A, Bachmann M, Sternberg A, Bardow A, Armstrong K, Michailos S, McCord S,
Zaragoza AV, Styring P, Marxen A, Naims H, Cremonese L, Strunge T, Olfe-Kräutlein B, Faber
G, Mangin C, Mason F, Stokes G, Williams E, Sick V. Techno-Economic Assessment & Life Cycle
Assessment Guidelines for CO2 Utilization (Version 1.1). 2020;(September).
[7]
Jungbluth N, Stucki M FR. Photovoltaics. In Sachbilanzen von Energiesystemen: Grundlagen
für den ökologischen Vergleich von Energiesystemen und den Einbezug von Energiesystemen
in Ökobilanzen für die Schweiz. ecoinvent report No. 6-XII. Swiss Cent Life Cycle Invent
Dübendorf, CH. 2009;16–69(6–XII).