Electrocatalytic Activity of Cobalt Ferrite Nanoparticles for Solar Thermochemical Hydrogen Production

Neil%Verma,%Nicole%Pacheco,%and%Jan%B.%Talbot%Chemical%Engineering%Program,%UCSD,%La%Jolla,%CA%92093%

Department%of%NanoEngineering,%UCSD,%La%Jolla,%CA%92093%%

Conclusions !  Deposits from EPD of cobalt ferrite in 90% water/10% IPA with 0.5

mM CTAB showed the highest activity on graphite felt

!  Thick depositions with slight cracking tend to have better electrochemical activity compared to sparse depositions

!  Cobalt ferrite nanoparticles made via co-precipitation method

!  Particle size: 20 ± 5 nm !  Energy-dispersive x-ray spectroscopy (EDX) utilized to verify

composition of particles !  2 g/L cobalt ferrite nanoparticles put into different baths: 100%

ethanol (E), 90% water/10% isopropanol (IPA) with 0.5 mM (Clow) or 1 mM (Chigh) of surfactant hexadecyltrimethylammonium bromide (CTAB)

!  Improve anodic reaction of ammonium sulfite to ammonium sulfate utilizing cobalt ferrite nanoparticle electrocatalysts

!  Vary EPD conditions in order to improve the effectiveness of the electrocatalysts

!  Compare the impact of different EPD bath chemistries on electrochemical results

!  Analyze the effects of deposit morphology on electrocatalytic ability

!  Purpose of this research is to study the use of cobalt ferrite nanoparticles as an electrocatalyst for the solar sulfur-ammonia thermochemical cycle

!  Electrophoretic deposition (EPD) is used as a method to coat felt substrates with cobalt ferrite nanoparticles

!  EPD is a promising technique: – Apparatus is cost-effective and simple – Deposition thickness of nanoparticle coatings controlled by

deposition time and applied voltage

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Cur

rent

(mA

/cm

2 )

Applied Voltage (V vs. NHE)

CLow (40 V, 219 mA, 10.4 mg) E (40 V, 29 mA, 6.0 mg) CHigh (21 V, 59 mA, 14.6 mg) Blank Felt

Introduction1

Objectives

Electrochemical Activity on Graphite Felt Substrates

Scanning Electron Microscope Imaging

Synthesis of Cobalt Ferrite Nanoparticles

Electrophoretic Deposition Set-Up

!  EPD experimental conditions: – Applied voltage: 21-40 V – Deposition time: 1 min – Substrate: 6 mm thick graphite felt – 2 cm gap between electrodes – Deposits baked in vacuum oven

for 1 hr

!  Standard three-compartment electrode system: – Reference electrode: standard calomel electrode (SCE) – Working electrode: EPD deposit on graphite felt – Counter electrode: 8 cm2 graphite cloth

!  CLow and E samples were soaked 72 hr and CHigh soaked 24 hr in 2 M ammonium sulfite to increase reproducibility

!  Electrochemical activity determined from linear sweep voltammetry of 2 cm2 EPD deposits at a scan rate of 50 mV/s

Current density vs. applied voltage for electrochemical activity of EPD deposits on graphite felt in 2 M ammonium sulfite1

Substrate 100 mL beaker

Aluminum anode

Potentiostat (21-40 V) ΔV

Aluminum anode

Blank graphite felt

CLow (40 V, 219 mA, 1 min, 10.4 mg) on graphite felt

Co-precipitation of cobalt ferrite2

Oxidation of ammonium sulfite to ammonium sulfate1

Future Work !  Optimize EPD conditions in order to enhance electrochemical activity

of catalysts

!  Further explore the effects of morphology on electrocatalytic activity

References 1.  N. Pacheco, N. Verma, K. Haider, and J.B. Talbot, Electrophoretic Deposition of Nanoparticles as

Electrocatalysts for Electrolysis in the Solar Sulfur Ammonia Hydrogen Production, to be published in Key Engineering Materials (2015).

2.  Z. Zi, Y. Sun, X. Zhu, Z. Yang, J. Dai, and W. Song, Journal of Magnetism and Magnetic Materials, 321 (2009) 1251-1255.