Zhen Yu Koh - Academia.edu (original) (raw)

Papers by Zhen Yu Koh

Journal of Materials Chemistry A, 2014

ABSTRACT We report a novel method to prepare cuprous sulfide counter electrodes by ion exchange o... more ABSTRACT We report a novel method to prepare cuprous sulfide counter electrodes by ion exchange of ZnS. The ZnS film is deposited on a porous ITO electrode beforehand by successive ionic layer adsorption and reaction, and converted into cuprous sulfide upon ion exchange for a short period of time. Using the cuprous sulfide counter electrodes, CdSe-sensitized solar cells exhibit a much higher photovoltaic performance as compared to their platinum counterpart, achieving a power conversion efficiency of 4.78%. Such an ion exchange process is promising to fabricate other sulfide counter electrodes, such as PbS, CoS, etc.

Biosensing II, 2009

A successful detection of inherently weak Raman signal from molecules is possible with giant enha... more A successful detection of inherently weak Raman signal from molecules is possible with giant enhancement of signal by the process of surface-enhanced Raman scattering (SERS). The SERS-induced enhancement is typically achieved when the molecules adsorbed onto the surface of a noble-metal substrate with nanometric roughness. Such SERS-substrate could be economically fabricated by convective assembly of polystyrene beads followed by metal deposition. The characterization of mono-metallic substrate showed that the SERS enhancement factor increases with increasing thickness of Ag or Au, with Ag-substrate giving the greatest SERS enhancement. However, the formation of silver oxide layer could reduce the shelf-life of the Ag-substrate. Alternatively, Au is also used as the coating material owing to its chemical inertness and biocompatibility. Despite the decent enhancement of the Au-substrate, Au-layer was found to be unstable after prolonged incubation in crystal violet solution. The inherent deficiency in adhesiveness of Au to the glass limits its use as a reliable and cost-effective substrate. In an attempt to improve the SERS-substrate, bimetallic substrate was fabricated by depositing the Au-film, as a protective layer, on the Ag-substrate. In this case, the top layer of Au of the bimetallic substrate remained intact after chemical treatment. Furthermore, the bimetallic substrate was shown to give comparable level of enhancement as an Ag-substrate by choosing a proper thickness ratio of the bimetallic layers. The result suggests that the design of bimetallic substrate could be optimized to maximize the SERS enhancement while retaining a decent stability after laser illumination and chemical treatment. Our findings suggest that bimetallic substrates are potentially useful for a reliable SERS-based biosensing.

Metal film over nanosphere (MFON) has been employed as a reproducible and predictable SERS-active... more Metal film over nanosphere (MFON) has been employed as a reproducible and predictable SERS-active device in biosensing applications. In addition to its economic fabrication process, such substrate can be further processed to a prism-structure with increased SERS enhancement and wider Plasmon tunability. In this work, we investigate an alternative coating method to deposit a larger area of well-ordered PS beads with different sizes (ø=100nm and 400nm) onto a glass. The result suggests that the proposed well-coating technique can be suitably used to form closely-packed PS beads with diameter less than 100nm for developing MFON substrates.

The Journal of Physical Chemistry C, 2014

Nonvolatile electrolyte solutions are necessary for dye-sensitized solar cells (DSCs) with good l... more Nonvolatile electrolyte solutions are necessary for dye-sensitized solar cells (DSCs) with good long-term stability. Such electrolytes usually contain room-temperature ionic liquids (RTILs) and consequently possess higher viscosity and ionic strength than the volatile electrolytes used in current champion cells. In this study, we systematically investigated the effect of an RTIL additive on the performance of DSCs employing either a classical Ru-complex dye or a recently developed organic D-A-π-A dye, in combination with either I − /I 3 − or [Co(bpy) 3 ] 2+/3+ as redox mediator. Using impedance spectroscopy and transient absorption measurements under various background illumination intensities, recombination and regeneration kinetics were examined. Recombination is accelerated in the I − /I 3 − devices upon addition of RTIL, regardless of the dye used, but it is retarded in the [Co(bpy) 3 ] 2+/3+ devices. Addition of RTIL slowed regeneration in I − /I 3 − devices for both sensitizers, marginally accelerated it for [Co(bpy) 3 ] 2+/3+ with the Ru-complex dye, and did not significantly affect it for [Co(bpy) 3 ] 2+/3+ with the D-A-π-A dye. We show that these findings cannot be explained by diffusion limitations caused by increased solution viscosity or by a shift in the TiO 2 conduction band relative to the electrolyte redox level. These findings should be useful for future optimization of RTIL-based DSCs.

Physical Chemistry Chemical Physics, 2012

Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobilit... more Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobility are essential for efficient charge separation and collection in PbS-sensitized solar cells. In the present study, mesoscopic SnO(2) was investigated as an alternative photoanode to the commonly used TiO(2) and examined comprehensively in PbS-sensitized liquid junction solar cells. To exploit the capability of PbS in an optimized structure, cascaded nPbS/nCdS and alternate n(PbS/CdS) layers deposited by a successive ionic layer adsorption and reaction method were systematically scrutinized. It was observed that the surface of SnO(2) has greater affinity to the growth of PbS compared with TiO(2), giving rise to much enhanced light absorption. In addition, the deposition of a CdS buffer layer and a ZnS passivation layer before and after a PbS layer was found to be beneficial for efficient charge separation. Under optimized conditions, cascaded PbS/CdS-sensitized SnO(2) exhibited an unprecedented photocurrent density of 17.38 mA cm(-2) with pronounced infrared light harvesting extending beyond 1100 nm, and a power conversion efficiency of 2.23% under AM 1.5, 1 sun illumination. In comparison, TiO(2) cells fabricated under similar conditions showed much inferior performance owing to the less efficient light harnessing of long wavelength photons. We anticipate that the systematic study of PbS-sensitized solar cells utilizing different metal oxide semiconductors as electron transporters would provide useful insights and promote the development of semiconductor-sensitized mesoscopic solar cells employing panchromatic sensitizers.

Journal of Raman Spectroscopy, 2012

We investigate the plasmonic enhancement arising from bimetallic (Au/Ag) hierarchical structure a... more We investigate the plasmonic enhancement arising from bimetallic (Au/Ag) hierarchical structure and address the fundamental issues relating to the design of multilayered nanostructures for surface-enhanced Raman scattering (SERS) spectroscopy. SERSactive nanosphere arrays with Ag underlayer and Au overlayer were systematically constructed, with the thickness of each layer altered from 40 to 320 nm. The SERS responses of the resultant bimetallic structures were measured with 2-naphthalenethiol dye as the test sample. The results confirm the dependency of SERS enhancement on the thickness ratio (Au : Ag). Compared with Au-arrays, our optimized bimetallic structures, which exhibit nanoprotrusions on the nanospheres, were found to be 2.5 times more SERS enhancing, approaching the enhancement factor of an Ag-array. The elevated SERS is attributed to the formation of effective hot-spots associated with increased roughness of the outer Au film, resulting from subsequent sputtering of Au granules on a roughened Ag surface. The morphology and reflectance studies suggest that the SERS hot-spots are distributed at the junctions of interconnected nanospheres and over the nanosphere surface, depending on the thickness ratio between the Au and Ag layers. We show that, by varying the thickness ratio, it is possible to optimize the SERS enhancement factor without significantly altering the operating plasmon resonance wavelength, which is dictated solely by the size of the underlying nanospheres template. In addition, our bimetallic substrates show long-term stability compared with previously reported Ag-arrays, whose SERS efficiency drops by 60% within a week because of oxidation. These findings demonstrate the potential of using such a bimetallic configuration to morphologically optimize any SERS substrate for sensing applications that demand huge SERS enhancement and adequate chemical stability.

Journal of Materials Chemistry, 2012

ABSTRACT Semiconductor-sensitized TiO2 solar cells employing CdSe as a light absorber demonstrate... more ABSTRACT Semiconductor-sensitized TiO2 solar cells employing CdSe as a light absorber demonstrate superior photovoltaic performance to the best-performing cascaded CdS/CdSe cells with practically identical optical density in the study. A careful comparison between CdSe and CdS/CdSe sensitized cells reveals that while CdS can greatly promote the subsequent growth of CdSe in the cascade electrodes and hence light harvesting, the presence of a CdS buffer layer impedes the injection of electrons from CdSe to TiO2 and accelerates charge recombination at the TiO2/sensitizer interface. As a result, better performance was achieved with CdSe-sensitized solar cells when light absorption is identical to that of CdS/CdSe cells, making the CdS buffer layer redundant. CdSe-sensitized TiO2 solar cells incorporating light scattering layers and an aqueous polysulfide electrolyte yielded an unprecedented power conversion efficiency of up to 5.21% under simulated AM 1.5, 100 mW cm-2 illumination.

Journal of Biomedical Optics, 2009

The control of image contrast is essential toward optimizing a contrast enhancement procedure in ... more The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography ͑OCT͒. In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2ϫ 10 9 particles/ ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor ͑EGFR͒ surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

Chemical Communications, 2014

We demonstrate an efficient D-A-π-A sensitizer with a benzothiadiazole-cyclopentadithiophene [cor... more We demonstrate an efficient D-A-π-A sensitizer with a benzothiadiazole-cyclopentadithiophene [corrected] moiety as the spacer in a triphenylamine organic dye for dye-sensitized solar cells. The dye has a broad visible light absorption range up to 800 nm. A power conversion efficiency >9% has been achieved using a [Co(bpy)3](2+/3+)-based electrolyte.

Advanced Materials, 2013

We demonstrate a novel bulk heterojunction structure based on a mesoporous TiO2 substrate, PbS qu... more We demonstrate a novel bulk heterojunction structure based on a mesoporous TiO2 substrate, PbS quantum dots (QDs), and a ZnS dielectric medium. The galena PbS QD arrays embedded in an amorphous ZnS matrix are adopted to fill up the mesoporous TiO2 electrode with an in situ approach, i.e., successive ionic layer adsorption and reaction. The inorganic ZnS resembles the capping material normally used in colloidal QDs to control the size of PbS.

Advanced Functional Materials, 2014

ACS Nano, 2011

Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar c... more Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar cells is relatively slow when compared to electron transfer from CdSe to TiO 2 . Controlled exposure of cadmium chalcogenide surfaces to copper ions followed by immersion in sulfide solution promotes development of the interfacial Cu x S layer, which mediates hole transfer to polysulfide electrolyte by collection of photogenerated holes from CdSe. In addition, Cu x S was also found to interact directly with defect states on the CdSe surface and quench emission characteristic of electron traps resulting from selenide vacancies. Together these effects were found to work in tandem to deliver 6.6% power conversion efficiency using Mn-doped CdS and CdSe cosensitized quantum dot solar cells. Development of an n−p interfacial junction at the photoanode−electrolyte interface in quantum dot solar cells unveils new means for designing high efficiency liquid junction solar cells.

ACS Applied Materials & Interfaces, 2013

A nickel salt−urea−H 2 O ternary system has been developed for the large-scale synthesis of hiera... more A nickel salt−urea−H 2 O ternary system has been developed for the large-scale synthesis of hierarchical α-Ni(OH) 2 microspheres, the solid precursor for the subsequent topotactic transition to NiO upon calcination. In this facile synthetic system, hierarchical structure is self-assembled under the cooperative direction of urea and anions in nickel salts. Thus, simply tuning the Ni salts leads to the selective construction of urchin and flowerlike hierarchical α-Ni(OH) 2 and NiO microspheres consisting of radial 1D nanowires and 2D nanoplates, respectively. The obtained NiO microspheres possessing accessible nanopores, excellent structural stability and large surface area up to 130 m 2 /g show promising electrochemical performance in anodic lithium storage for lithium-ion battery.

Journal of Materials Chemistry A, 2014

ABSTRACT We report a novel method to prepare cuprous sulfide counter electrodes by ion exchange o... more ABSTRACT We report a novel method to prepare cuprous sulfide counter electrodes by ion exchange of ZnS. The ZnS film is deposited on a porous ITO electrode beforehand by successive ionic layer adsorption and reaction, and converted into cuprous sulfide upon ion exchange for a short period of time. Using the cuprous sulfide counter electrodes, CdSe-sensitized solar cells exhibit a much higher photovoltaic performance as compared to their platinum counterpart, achieving a power conversion efficiency of 4.78%. Such an ion exchange process is promising to fabricate other sulfide counter electrodes, such as PbS, CoS, etc.

Biosensing II, 2009

A successful detection of inherently weak Raman signal from molecules is possible with giant enha... more A successful detection of inherently weak Raman signal from molecules is possible with giant enhancement of signal by the process of surface-enhanced Raman scattering (SERS). The SERS-induced enhancement is typically achieved when the molecules adsorbed onto the surface of a noble-metal substrate with nanometric roughness. Such SERS-substrate could be economically fabricated by convective assembly of polystyrene beads followed by metal deposition. The characterization of mono-metallic substrate showed that the SERS enhancement factor increases with increasing thickness of Ag or Au, with Ag-substrate giving the greatest SERS enhancement. However, the formation of silver oxide layer could reduce the shelf-life of the Ag-substrate. Alternatively, Au is also used as the coating material owing to its chemical inertness and biocompatibility. Despite the decent enhancement of the Au-substrate, Au-layer was found to be unstable after prolonged incubation in crystal violet solution. The inherent deficiency in adhesiveness of Au to the glass limits its use as a reliable and cost-effective substrate. In an attempt to improve the SERS-substrate, bimetallic substrate was fabricated by depositing the Au-film, as a protective layer, on the Ag-substrate. In this case, the top layer of Au of the bimetallic substrate remained intact after chemical treatment. Furthermore, the bimetallic substrate was shown to give comparable level of enhancement as an Ag-substrate by choosing a proper thickness ratio of the bimetallic layers. The result suggests that the design of bimetallic substrate could be optimized to maximize the SERS enhancement while retaining a decent stability after laser illumination and chemical treatment. Our findings suggest that bimetallic substrates are potentially useful for a reliable SERS-based biosensing.

Metal film over nanosphere (MFON) has been employed as a reproducible and predictable SERS-active... more Metal film over nanosphere (MFON) has been employed as a reproducible and predictable SERS-active device in biosensing applications. In addition to its economic fabrication process, such substrate can be further processed to a prism-structure with increased SERS enhancement and wider Plasmon tunability. In this work, we investigate an alternative coating method to deposit a larger area of well-ordered PS beads with different sizes (ø=100nm and 400nm) onto a glass. The result suggests that the proposed well-coating technique can be suitably used to form closely-packed PS beads with diameter less than 100nm for developing MFON substrates.

The Journal of Physical Chemistry C, 2014

Nonvolatile electrolyte solutions are necessary for dye-sensitized solar cells (DSCs) with good l... more Nonvolatile electrolyte solutions are necessary for dye-sensitized solar cells (DSCs) with good long-term stability. Such electrolytes usually contain room-temperature ionic liquids (RTILs) and consequently possess higher viscosity and ionic strength than the volatile electrolytes used in current champion cells. In this study, we systematically investigated the effect of an RTIL additive on the performance of DSCs employing either a classical Ru-complex dye or a recently developed organic D-A-π-A dye, in combination with either I − /I 3 − or [Co(bpy) 3 ] 2+/3+ as redox mediator. Using impedance spectroscopy and transient absorption measurements under various background illumination intensities, recombination and regeneration kinetics were examined. Recombination is accelerated in the I − /I 3 − devices upon addition of RTIL, regardless of the dye used, but it is retarded in the [Co(bpy) 3 ] 2+/3+ devices. Addition of RTIL slowed regeneration in I − /I 3 − devices for both sensitizers, marginally accelerated it for [Co(bpy) 3 ] 2+/3+ with the Ru-complex dye, and did not significantly affect it for [Co(bpy) 3 ] 2+/3+ with the D-A-π-A dye. We show that these findings cannot be explained by diffusion limitations caused by increased solution viscosity or by a shift in the TiO 2 conduction band relative to the electrolyte redox level. These findings should be useful for future optimization of RTIL-based DSCs.

Physical Chemistry Chemical Physics, 2012

Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobilit... more Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobility are essential for efficient charge separation and collection in PbS-sensitized solar cells. In the present study, mesoscopic SnO(2) was investigated as an alternative photoanode to the commonly used TiO(2) and examined comprehensively in PbS-sensitized liquid junction solar cells. To exploit the capability of PbS in an optimized structure, cascaded nPbS/nCdS and alternate n(PbS/CdS) layers deposited by a successive ionic layer adsorption and reaction method were systematically scrutinized. It was observed that the surface of SnO(2) has greater affinity to the growth of PbS compared with TiO(2), giving rise to much enhanced light absorption. In addition, the deposition of a CdS buffer layer and a ZnS passivation layer before and after a PbS layer was found to be beneficial for efficient charge separation. Under optimized conditions, cascaded PbS/CdS-sensitized SnO(2) exhibited an unprecedented photocurrent density of 17.38 mA cm(-2) with pronounced infrared light harvesting extending beyond 1100 nm, and a power conversion efficiency of 2.23% under AM 1.5, 1 sun illumination. In comparison, TiO(2) cells fabricated under similar conditions showed much inferior performance owing to the less efficient light harnessing of long wavelength photons. We anticipate that the systematic study of PbS-sensitized solar cells utilizing different metal oxide semiconductors as electron transporters would provide useful insights and promote the development of semiconductor-sensitized mesoscopic solar cells employing panchromatic sensitizers.

Journal of Raman Spectroscopy, 2012

We investigate the plasmonic enhancement arising from bimetallic (Au/Ag) hierarchical structure a... more We investigate the plasmonic enhancement arising from bimetallic (Au/Ag) hierarchical structure and address the fundamental issues relating to the design of multilayered nanostructures for surface-enhanced Raman scattering (SERS) spectroscopy. SERSactive nanosphere arrays with Ag underlayer and Au overlayer were systematically constructed, with the thickness of each layer altered from 40 to 320 nm. The SERS responses of the resultant bimetallic structures were measured with 2-naphthalenethiol dye as the test sample. The results confirm the dependency of SERS enhancement on the thickness ratio (Au : Ag). Compared with Au-arrays, our optimized bimetallic structures, which exhibit nanoprotrusions on the nanospheres, were found to be 2.5 times more SERS enhancing, approaching the enhancement factor of an Ag-array. The elevated SERS is attributed to the formation of effective hot-spots associated with increased roughness of the outer Au film, resulting from subsequent sputtering of Au granules on a roughened Ag surface. The morphology and reflectance studies suggest that the SERS hot-spots are distributed at the junctions of interconnected nanospheres and over the nanosphere surface, depending on the thickness ratio between the Au and Ag layers. We show that, by varying the thickness ratio, it is possible to optimize the SERS enhancement factor without significantly altering the operating plasmon resonance wavelength, which is dictated solely by the size of the underlying nanospheres template. In addition, our bimetallic substrates show long-term stability compared with previously reported Ag-arrays, whose SERS efficiency drops by 60% within a week because of oxidation. These findings demonstrate the potential of using such a bimetallic configuration to morphologically optimize any SERS substrate for sensing applications that demand huge SERS enhancement and adequate chemical stability.

Journal of Materials Chemistry, 2012

ABSTRACT Semiconductor-sensitized TiO2 solar cells employing CdSe as a light absorber demonstrate... more ABSTRACT Semiconductor-sensitized TiO2 solar cells employing CdSe as a light absorber demonstrate superior photovoltaic performance to the best-performing cascaded CdS/CdSe cells with practically identical optical density in the study. A careful comparison between CdSe and CdS/CdSe sensitized cells reveals that while CdS can greatly promote the subsequent growth of CdSe in the cascade electrodes and hence light harvesting, the presence of a CdS buffer layer impedes the injection of electrons from CdSe to TiO2 and accelerates charge recombination at the TiO2/sensitizer interface. As a result, better performance was achieved with CdSe-sensitized solar cells when light absorption is identical to that of CdS/CdSe cells, making the CdS buffer layer redundant. CdSe-sensitized TiO2 solar cells incorporating light scattering layers and an aqueous polysulfide electrolyte yielded an unprecedented power conversion efficiency of up to 5.21% under simulated AM 1.5, 100 mW cm-2 illumination.

Journal of Biomedical Optics, 2009

The control of image contrast is essential toward optimizing a contrast enhancement procedure in ... more The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography ͑OCT͒. In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2ϫ 10 9 particles/ ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor ͑EGFR͒ surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

Chemical Communications, 2014

We demonstrate an efficient D-A-π-A sensitizer with a benzothiadiazole-cyclopentadithiophene [cor... more We demonstrate an efficient D-A-π-A sensitizer with a benzothiadiazole-cyclopentadithiophene [corrected] moiety as the spacer in a triphenylamine organic dye for dye-sensitized solar cells. The dye has a broad visible light absorption range up to 800 nm. A power conversion efficiency >9% has been achieved using a [Co(bpy)3](2+/3+)-based electrolyte.

Advanced Materials, 2013

We demonstrate a novel bulk heterojunction structure based on a mesoporous TiO2 substrate, PbS qu... more We demonstrate a novel bulk heterojunction structure based on a mesoporous TiO2 substrate, PbS quantum dots (QDs), and a ZnS dielectric medium. The galena PbS QD arrays embedded in an amorphous ZnS matrix are adopted to fill up the mesoporous TiO2 electrode with an in situ approach, i.e., successive ionic layer adsorption and reaction. The inorganic ZnS resembles the capping material normally used in colloidal QDs to control the size of PbS.

Advanced Functional Materials, 2014

ACS Nano, 2011

Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar c... more Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar cells is relatively slow when compared to electron transfer from CdSe to TiO 2 . Controlled exposure of cadmium chalcogenide surfaces to copper ions followed by immersion in sulfide solution promotes development of the interfacial Cu x S layer, which mediates hole transfer to polysulfide electrolyte by collection of photogenerated holes from CdSe. In addition, Cu x S was also found to interact directly with defect states on the CdSe surface and quench emission characteristic of electron traps resulting from selenide vacancies. Together these effects were found to work in tandem to deliver 6.6% power conversion efficiency using Mn-doped CdS and CdSe cosensitized quantum dot solar cells. Development of an n−p interfacial junction at the photoanode−electrolyte interface in quantum dot solar cells unveils new means for designing high efficiency liquid junction solar cells.

ACS Applied Materials & Interfaces, 2013

A nickel salt−urea−H 2 O ternary system has been developed for the large-scale synthesis of hiera... more A nickel salt−urea−H 2 O ternary system has been developed for the large-scale synthesis of hierarchical α-Ni(OH) 2 microspheres, the solid precursor for the subsequent topotactic transition to NiO upon calcination. In this facile synthetic system, hierarchical structure is self-assembled under the cooperative direction of urea and anions in nickel salts. Thus, simply tuning the Ni salts leads to the selective construction of urchin and flowerlike hierarchical α-Ni(OH) 2 and NiO microspheres consisting of radial 1D nanowires and 2D nanoplates, respectively. The obtained NiO microspheres possessing accessible nanopores, excellent structural stability and large surface area up to 130 m 2 /g show promising electrochemical performance in anodic lithium storage for lithium-ion battery.