V (V vs Ag/AgCl)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

Dark measurement

UV ON

Time (sec)

0 1000 2000 3000 4000 5000

I (m

A/c

m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

V (V vs Ag/AgCl)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Dark measurement

UV ON

Time (sec)

0 1000 2000 3000 4000 5000

I (m

A/c

m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

V (V vs Ag/AgCl)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Dark measurement

UV ON

AbstractInGaN/GaN core-shell structure have gained increasing interest as photo anodes for water-splitting due to their adjustable band gap, whichcan be tuned to absorb a wide range of the solar spectrum. Although promising, their stability in liquid environments has been hindering theiruse in photoelectrochemical (PEC) water-splitting. In an attempt to understand and evaluate these instabilities, we tested GaN nanorods indifferent electrolytes. Cyclic voltammetry and time dependant photocurrent data are presented, together with SEM images and EDX, beforeand after etching, to show the effect of the tests on the specimens. Despite these instabilities, our initial results, obtained on InGaN/GaNcore-shell nanorods structures showed promising results.

Evaluating the performance of GaN and InGaN/GaN core-shell nanorods structures as photo anodes in photoelectrochemical

water splittingV. Adamaki1, E. D. Le Boulbar2, A. Sergejevs2, C. Clarke2, C. R. Bowen1

1Mechanical Engineering Department, University of Bath, BA2 7AY, UK2Electrical Engineering Department, University of Bath, BA2 7AY, UK

InGaN/GaN core-shell nanorods

Photoelectrochemical (PEC) measurements

The research leading to the materials development and characterisation was from the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement no. 320963 on Novel Energy Materials, Engineering, Science and Integrated Systems (NEMESIS).

Energy Harvesting 2016

• 3-electrode electrochemical system• Ag/AgCl reference electrode and a

platinum wire as a counter electrode in 0.1M Na2SO4 electrolyte

• 6 wavelengths UV to visible light• Homogeneous illumination

GaN nanorods

4326 SQW_blue (455nm)

V vs Ag/AgCl (V)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

OFF

ON_blue

InGaN/GaN under blue light (451.22nm)

Wavelength (nm)

IPCE (%)0 V vs SHE

IPCE (%) 0.74 V vs SHE

451.22 1.23 13.4

527.18 1.34 10.7

593.57 0 0.84

629.62 0 0.18

!

After a few runs…

4335 6MQWs_blue (455nm)

V vs Ag/AgCl (V)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

-0.01

0.00

0.01

0.02

0.03

0.04

OFF

ON_blue

Reduced photocurrent under blue light (451.22nm)

583 nm2 μm

412 nm

Nanorodssites

• Electrochemically stable at 0 V vs SHE.• Nanorods etched when potential is applied• Test different electrolyte

At

0 V

vs

SHE

At

0.6

V v

s SH

EA

t 1

V v

s SH

E

Time (sec)

0 1000 2000 3000 4000 5000

I (m

A/c

m2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

V (V vs Ag/Ag/Cl)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

I (m

A/c

m2)

0.0

0.5

1.0

1.5

2.0

2.5

Dark measurement

UV ON

OFF

OFF

OFFOFF

ON

ON

ON

GaN nanorods

Line spectrum along the length of the InGaN/GaN core-shell

structure

0.0 0.5 1.0 1.5 2.0 2.5 3.0

distance (µm)

2.0

2.5

3.0

3.5

en

erg

y (

eV

)

1

10

100

1000

CL

inte

ns

ity (c

ou

nts

)

GaN/InGaN regrowth

Passivation layer

Metal maskPlasma etching

Nanorod array

Fabrication process

GaN under UV light (368 nm)

ON