Electrochemical potential tuned solar water splitting

Licht, Stuart; Halperin, Leonid; Kalina, Michael; Zidman, Martina; Halperin, Nadezhda

doi:10.1039/b309397b

Cited by 51 publications

(85 citation statements)

References 9 publications

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“…This was achieved in molten sodium hydroxide heated by sub-bandgap illumination at high solar efficiency in a cost effective manner. 9,10 One high temperature alternative, to water splitting in molten salts, is the developing field of solid oxide water splitting. 11 However, the molten electrolyte is advantageous by providing a significantly higher density of reactive water sites in prox- * Electrochemical Society Member.…”

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confidence: 99%

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Licht

Liu

Cui

et al. 2016

J. Electrochem. Soc.

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This study explores a new high temperature molten hydroxide domain to electrochemically split water into hydrogen fuel. Hydrogen fuel, if produced without greenhouse gas emissions, is a promising fuel for transportation. This study opens a pathway to low energy water splitting and the electrolytic production of hydrogen fuel without carbon dioxide emission. A wide range of pure and mixed alkali and alkali earth hydroxide electrolytes are explored at temperatures ranging from 200 to 700 • C. Higher temperature leads to improved (lower voltage) water splitting and improved rates of charge transfer, but carries challenges (increased rates of parasitic side reactions as the molten electrolytes dehydrate with increasing temperature). This study extends the range of hydrogen formation in alkaline electrolysis water splitting to over 600 • C, and demonstrates that lithium and/or barium hydroxide electrolytes remain hydrated at high temperatures, and in the high temperature domain are advantageous over sodium or potassium hydroxide electrolytes. In pure LiOH, the coulombic efficiency for hydrogen generation decreases with temperature and is measured respectively at η H 2 = 88%, 21%, 4% and 0%, respectively at 500, 600, 700 and 800 • Hydrogen has advantageous features compared to fossil fuels. It has a higher specific energy, is not polluting, has a combustion product of water, and in particular it does not emit the greenhouse gas carbon dioxide. Challenges of hydrogen storage are being addressed and hydrogen powered vehicles have been introduced to the commercial marketplace.1-4 Unfortunately, the predominant fraction of hydrogen generated today is produced by steam reformation of fossil fuel by reacting the fossil fuel with steam to release H 2 and CO 2 . Steam reformation is a substantial source of CO 2 emissions, negating the climate mitigation effect of using H 2 as a fuel. Thus, a process to efficiently generate hydrogen without carbon dioxide emissions is needed.The development of electrolytic splitting of water dates back to 1802. 5 The electrolysis of water produces hydrogen and oxygen directly without CO 2 emission (if the energy source used to generate the electricity did not release CO 2 ). Utilization of renewable or nuclear energy to generate the electricity for this electrolysis can drive this electrolytic water splitting to produce hydrogen as a fuel without carbon dioxide emissions. The most abundant of renewable energy resource for electrical generation is solar energy, and as early as 2001 we were driving stable solar electrolytic water splitting to hydrogen fuels at over 18% solar to chemical energy conversion by using efficient multiple bandgap solar cells.6 One of the challenges to the use of illuminated junctions to drive electrochemical or photoelectrochemical water splitting is that the bandgap of efficient semiconductors lies in the visible spectrum which generate a photo-potential less than the minimum needed rest potential of 1.23 volt required to split water to hydrogen and oxygen at room te...

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confidence: 99%

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Licht

Liu

Cui

et al. 2016

J. Electrochem. Soc.

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“…larger voltage drop. A source of error in measuring the total etch charge could be the additional electrolysis of H 2 O into H 2 and O 2 , which theoretically occurs already at 1-V potential difference to the reference electrode [22]. The premature stopping of the etching on the samples with a Cr adhesion layer is explained by the electrochemical etching also attacking the Fig.…”

Section: Etch Characterizationmentioning

confidence: 99%

Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices

Sterner

Roxhed

Stemme

et al. 2011

J. Microelectromech. Syst.

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Abstract-This paper presents a novel electrochemically assisted wet-etching method for maskless selective removal of metal layers. This method has been developed as the key process step for enabling the fabrication of low-loss 3-D micromachined silicon-oninsulator-based radio-frequency microelectromechanical systems transmission line components, consisting of a silicon core in the device layer covered by a gold metallization layer. For this application, the full-wafer sputtered metallization layer must be locally removed on the handle layer to guarantee for a well-defined and low-loss coplanar-waveguide propagation mode in the slots of the transmission line. It is not possible to use conventional photolithography or shadow masking. Gold areas to be etched are biased by a 1.2-V potential difference to a saturated calomel reference electrode in a NaCl(aq) solution. The measured etch rate of the proposed local electrochemically biased etching process is 520 nm/min, and no detectable etching was observed on unbiased areas even after a 1-h etch. The suitability of different adhesion layers has been investigated, and Ti-based adhesion layers were found to result in the highest yield. The new etching method has been successfully applied for the fabrication of transmission lines with integrated microswitches, lowering the insertion loss of the waveguide at 10 GHz from 1.3 to 0.3 dB/mm. The issue of unwanted thin metallic connections caused by secondary deposition during sputtering is discussed but found not to significantly affect the process yield. Finally, local removal of gold on isolated features even within the device layer is presented for locally removing the metallization on stoppers of laterally moving electrostatic actuators, to drastically reduce the mechanical wear on stopper tips.[ 2010-0326]Index Terms-Coplanar waveguide (CPW), radio-frequency (RF) microelectromechanical systems (MEMS), transmission lines.

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“…The electrolysis potential is measured as the voltage between the anode and the cathode at constant current. We have previously reported on STEP cathode or oxygen anode potentials in a variety of molten carbonates [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] During electrolysis, the iron product accumulates at the cathode, which is subsequently removed and cooled. Details of STEP electrolysis are provided in references [5][6][7][8].…”

Section: Electrolysismentioning

confidence: 99%

“…Fundamental, electrochemical, and impurity effects on STEP iron have been investigated [8], and the general effects of alkali earth and hydroxide on STEP processes in molten carbonates have been reported [14][15][16][17][18][19][20]. The fundamental increase in solar electrolysis efficiency with the use of solar thermal has been analyzed for CO 2 and H 2 O splitting theoretically [10][11][12] and experimentally [13][14][15] and the fundamental endogenic decrease in electrochemical potential with the increasing temperature demonstrated for a number of STEP processes [10][11][12][13][14][15][16][17][18][19][20]. The requisite solar thermal heating for any given process will depend on the current density, which controls the overpotential and the net difference between the thermoneutral potential and the applied electrolysis potential.…”

Section: Introductionmentioning

confidence: 99%

“…The general solar thermal electrochemical process (STEP) of sunlight to decrease (endogenic) electrolysis potentials leads to high solar energy conversion efficiencies [6][7][8][9][10][11]. A variety of other STEP electrolyses have been demonstrated to decrease CO 2 including the production of cement, ammonia, fuels, and carbon for the direct removal of atmospheric or smokestack carbon dioxide [10][11][12][13][14][15][16][17][18][19][20]. Fundamental, electrochemical, and impurity effects on STEP iron have been investigated [8], and the general effects of alkali earth and hydroxide on STEP processes in molten carbonates have been reported [14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Sustainable Electrochemical Synthesis of Large Grain- or Catalyst-Sized Iron

Wang

Licht

2016

J. Sustain. Metall.

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Electrolytic production of iron in molten salts by splitting iron oxide into iron metal and O 2 is a low-carbon footprint alternative to the massive CO 2 emissions associated with conventional carbothermal iron production and permits. This study advances a CO 2 -free method for iron production, by modifying iron electrosynthesis in molten Li 2 CO 3 to control iron product particle size and by decreasing the electrolyte extracted with the pure iron product. We present the first study of electrolytic iron micro-morphology as formed from iron, and demonstrate it is strongly influenced by the deposition conditions. Particle size and morphology are critical characteristics in a variety of metal applications. In this study, large (*500 lm) iron particles are formed at low current densities during extended electrolysis, or at high Fe(III) concentrations, and small (*10 lm) at high current density and low Fe(III). Deposited Fe is fiber shaped from equal molals of Fe 2 O 3 and Li 2 O, but particle-like from electrolytes with surplus Li 2 O. Iron is formed at high current efficiency, and the observed electrolysis potential decreases with (i) the decreasing current density, (ii) addition of Li 2 O, (iii) the increasing anode area, and (iv) the increasing temperature.

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Electrochemical potential tuned solar water splitting

Cited by 51 publications

References 9 publications

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Comparison of Alternative Molten Electrolytes for Water Splitting to Generate Hydrogen Fuel

Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices

Sustainable Electrochemical Synthesis of Large Grain- or Catalyst-Sized Iron

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