title: Fabrication and characterisation of nickel/yttria stabilised zirconia cermet anodes for solid oxide fuel cells

authors: Brown, Michael Steven

abstract: The primary objective of this thesis was to study the Ni/YSZ system from powder preparation to electrochemical and morphological characterisation.

Nickel/yttria stabilised zirconia (YSZ) cermet systems are employed as anode materials in high temperature solid oxide fuel cell (SOFC) applications. The ionically conducting YSZ powder was modified, by sintering and milling to vary the particle distribution. This allowed the fabrication of cermet powders with varying particle sizes and therefore microstructures. Bimodal particle distributions were present for the milled YSZ, which indicated two particle sizes. The finest particles were individual YSZ particles of approximately 0.4 μm, and represented the grinding limit, which was independent of calcining temperature. The agglomerate size decreased and the amount of fine YSZ increased as milling times were extended.

A ‘paint’ consisting of the cermet powder (NiO/YSZ), a solvent, and a binder was developed in order to use a wet powder spraying (WPS®) technique, to apply the electrode layer to the electrolyte substrate. By this method, reproducible anodes with good morphological properties were produced. The slurry was prepared with ethanol as the solvent and a PVP binder, to form a stable suspension. 

Anode sintering temperature was studied with results indicating that a temperature of 1300 °C provided the optimum sintering effect. Anodes sintered at 1300 °C showed no agglomeration of NiO. There was no discernable increase of Ni particle size after reducing in hydrogen.

A number of Ni/YSZ cermet anodes consisting of 40 vol% nickel and 60 vol% YSZ were fabricated with varying thickness of the active layer. The anode materials were milled to the appropriate particle sizes, air-sprayed onto YSZ substrates and subsequently sintered to produce the anode component. The thicknesses ranged from 3.5 μm to 54 μm in order to find the minimum thickness of active layer for a high performance anode using the least material. The anodes were studied in an atmosphere of hydrogen, water and nitrogen in a 3-electrode setup. Impedance spectroscopy was carried out at a temperature of 1000 °C.

It was found that approximately 12 μm was the limiting thickness for a low polarisation resistance. Below a thickness of 12 μm, the polarisation resistance increased in an erratic manner as the reaction zone was reduced.

Ni/YSZ cermet anodes consisting of 90 vol% Ni and 10 vol% YSZ were fabricated in order to create an anode with significantly higher polarisation resistance. Hereby a structure-related impedance arc at high frequencies could be examined in detail.  The anode was studied in mixtures of hydrogen, water and nitrogen in a 3-electrode setup. Impedance measurements were carried out at temperatures ranging between 700°C and 1000°C. The present work confirmed that a high frequency arc from impedance spectroscopy data was indeed related to the structure of the cermet. 

Four types of Ni/YSZ anodes were characterised and compared to illustrate similarities and differences from state-of-the-art cermet anodes to coarse structure cermets to two-dimensional Ni anodes with significantly higher polarization resistance. The anode structure-dependent high frequency section of the impedance spectrum was studied.

The thesis concludes with recommendations for further investigations.

text: Fabrication and characterisation of nickel/yttria stabilised zirconia cermet anodes for solid oxide fuel cells The primary objective of this thesis was to study the Ni/YSZ system from powder preparation to electrochemical and morphological characterisation.

Nickel/yttria stabilised zirconia (YSZ) cermet systems are employed as anode materials in high temperature solid oxide fuel cell (SOFC) applications. The ionically conducting YSZ powder was modified, by sintering and milling to vary the particle distribution. This allowed the fabrication of cermet powders with varying particle sizes and therefore microstructures. Bimodal particle distributions were present for the milled YSZ, which indicated two particle sizes. The finest particles were individual YSZ particles of approximately 0.4 μm, and represented the grinding limit, which was independent of calcining temperature. The agglomerate size decreased and the amount of fine YSZ increased as milling times were extended.

A ‘paint’ consisting of the cermet powder (NiO/YSZ), a solvent, and a binder was developed in order to use a wet powder spraying (WPS®) technique, to apply the electrode layer to the electrolyte substrate. By this method, reproducible anodes with good morphological properties were produced. The slurry was prepared with ethanol as the solvent and a PVP binder, to form a stable suspension. 

Anode sintering temperature was studied with results indicating that a temperature of 1300 °C provided the optimum sintering effect. Anodes sintered at 1300 °C showed no agglomeration of NiO. There was no discernable increase of Ni particle size after reducing in hydrogen.

A number of Ni/YSZ cermet anodes consisting of 40 vol% nickel and 60 vol% YSZ were fabricated with varying thickness of the active layer. The anode materials were milled to the appropriate particle sizes, air-sprayed onto YSZ substrates and subsequently sintered to produce the anode component. The thicknesses ranged from 3.5 μm to 54 μm in order to find the minimum thickness of active layer for a high performance anode using the least material. The anodes were studied in an atmosphere of hydrogen, water and nitrogen in a 3-electrode setup. Impedance spectroscopy was carried out at a temperature of 1000 °C.

It was found that approximately 12 μm was the limiting thickness for a low polarisation resistance. Below a thickness of 12 μm, the polarisation resistance increased in an erratic manner as the reaction zone was reduced.

Ni/YSZ cermet anodes consisting of 90 vol% Ni and 10 vol% YSZ were fabricated in order to create an anode with significantly higher polarisation resistance. Hereby a structure-related impedance arc at high frequencies could be examined in detail.  The anode was studied in mixtures of hydrogen, water and nitrogen in a 3-electrode setup. Impedance measurements were carried out at temperatures ranging between 700°C and 1000°C. The present work confirmed that a high frequency arc from impedance spectroscopy data was indeed related to the structure of the cermet. 

Four types of Ni/YSZ anodes were characterised and compared to illustrate similarities and differences from state-of-the-art cermet anodes to coarse structure cermets to two-dimensional Ni anodes with significantly higher polarization resistance. The anode structure-dependent high frequency section of the impedance spectrum was studied.

The thesis concludes with recommendations for further investigations.

year: 1998

title: Do research assessment exercises raise the returns to publication quality? Evidence from the New Zealand market for academic economists

authors: Gibson, John

subjects: research assessment

abstract: Many countries have introduced research assessment exercises to help measure and raise the quality of research in their university sector. But there is little empirical evidence on how these exercises, such as the Quality Evaluation of the Performance Based Research Fund (PBRF) in New Zealand and the recently aborted Research Quality Framework (RQF) in Australia, affect the signals that researchers observe in the academic labour market. Since these assessments aim to raise research quality, individual academics should perceive rising returns to publication quality at the expense of the returns to quantity. Data we collected on the rank and publication records of New Zealand academic economists prior to the introduction of the PBRF and just after the second assessment round are used to estimate the changing returns to the quantity and quality of journal articles.

text: Do research assessment exercises raise the returns to publication quality? Evidence from the New Zealand market for academic economists Many countries have introduced research assessment exercises to help measure and raise the quality of research in their university sector. But there is little empirical evidence on how these exercises, such as the Quality Evaluation of the Performance Based Research Fund (PBRF) in New Zealand and the recently aborted Research Quality Framework (RQF) in Australia, affect the signals that researchers observe in the academic labour market. Since these assessments aim to raise research quality, individual academics should perceive rising returns to publication quality at the expense of the returns to quantity. Data we collected on the rank and publication records of New Zealand academic economists prior to the introduction of the PBRF and just after the second assessment round are used to estimate the changing returns to the quantity and quality of journal articles.

year: 2008-08

title: Birds vs. Clams: Assessing the impacts of South Island pied oystercatcher predation on Toheroa at Ripiro Beach, New Zealand

authors: Vallyon, Lolita-Maria Dolores

abstract: Managing the recovery of interacting species, such as predator and prey, is one of the most challenging factors of an ecosystem-based conservation approach. The actions taken to protect one species may be in conflict with the actions necessary to protect another. For example, the recovery of a predator in an ecosystem can lead to a significant conservation conflict between the protected predator and its protected prey. In these instances, research is required to determine whether a perceived conflict is in fact happening in order to inform proper management decisions. In New Zealand, a conservation conflict exists between an endemic, recovering shorebird, the South Island pied oystercatcher (Haematopus ostralegus finschi), and an endemic surf clam, the toheroa (Paphies ventricosa) at Ripiro Beach, Northland. The toheroa was overharvested until the populations collapsed, with commercial and recreational harvesting bans put in place by the 1970s. The toheroa has continued to decline, and the cause is currently unknown. Oystercatcher predation has been implicated as the reason toheroa populations have not recovered. There have even been calls to cull the birds to protect the clams. Currently, there is no information that would facilitate conservation management in determining the appropriate action to take. My thesis aimed to investigate the claims surrounding this perceived interspecific conflict. It sought to examine the predator-prey interactions between the two species by answering the following three questions: 1) what are the spatio-temporal associations between oystercatchers and toheroa, 2) what is the composition of the oystercatcher’s diet, and 3) what size toheroa are the birds taking? 
Bird surveys were conducted to examine the distribution of oystercatchers monthly from March 2019 to February 2020. Oystercatcher foraging behaviour was observed to collect information on prey type and prey location. Feeding holes left by oystercatcher bills at predation sites were examined to determine oystercatcher predation success. A population survey was conducted on toheroa beds exposed to oystercatcher predation versus control beds to assess if there were differences in the density and size structure between toheroa populations. 

Results did not support the hypothesis that the oystercatchers are the cause behind the limited recovery of the toheroa, but they did indicate that the birds may be having localised impacts. There was limited overlap with toheroa, as the birds were found predominantly at the southern half of Ripiro Beach and were only associated with two major toheroa beds. Observations found that bivalves are a significant food resource for oystercatchers and the birds have a high predation success rate. There was a significant difference in the density and size structure between toheroa populations in beds that were oystercatcher predation sites and those at no-predation sites. However, even in the areas with the most intense oystercatcher predation, toheroa have persisted over time. While there potentially is a small local impact, overall, the South Island pied oystercatcher is not responsible for the continuing decline of the toheroa across the whole of Ripiro Beach and are not causing devastation as claimed. 
The perceived conservation conflict between the two endemic species is likely incorrect. This research demonstrates the importance of acquiring information on interacting species prior to management action to protect one of those species. Information presented in this thesis can be used to support conservation managers in making informed decisions to protect both the toheroa and the South Island pied oystercatcher.

text: Birds vs. Clams: Assessing the impacts of South Island pied oystercatcher predation on Toheroa at Ripiro Beach, New Zealand Managing the recovery of interacting species, such as predator and prey, is one of the most challenging factors of an ecosystem-based conservation approach. The actions taken to protect one species may be in conflict with the actions necessary to protect another. For example, the recovery of a predator in an ecosystem can lead to a significant conservation conflict between the protected predator and its protected prey. In these instances, research is required to determine whether a perceived conflict is in fact happening in order to inform proper management decisions. In New Zealand, a conservation conflict exists between an endemic, recovering shorebird, the South Island pied oystercatcher (Haematopus ostralegus finschi), and an endemic surf clam, the toheroa (Paphies ventricosa) at Ripiro Beach, Northland. The toheroa was overharvested until the populations collapsed, with commercial and recreational harvesting bans put in place by the 1970s. The toheroa has continued to decline, and the cause is currently unknown. Oystercatcher predation has been implicated as the reason toheroa populations have not recovered. There have even been calls to cull the birds to protect the clams. Currently, there is no information that would facilitate conservation management in determining the appropriate action to take. My thesis aimed to investigate the claims surrounding this perceived interspecific conflict. It sought to examine the predator-prey interactions between the two species by answering the following three questions: 1) what are the spatio-temporal associations between oystercatchers and toheroa, 2) what is the composition of the oystercatcher’s diet, and 3) what size toheroa are the birds taking? 
Bird surveys were conducted to examine the distribution of oystercatchers monthly from March 2019 to February 2020. Oystercatcher foraging behaviour was observed to collect information on prey type and prey location. Feeding holes left by oystercatcher bills at predation sites were examined to determine oystercatcher predation success. A population survey was conducted on toheroa beds exposed to oystercatcher predation versus control beds to assess if there were differences in the density and size structure between toheroa populations. 

Results did not support the hypothesis that the oystercatchers are the cause behind the limited recovery of the toheroa, but they did indicate that the birds may be having localised impacts. There was limited overlap with toheroa, as the birds were found predominantly at the southern half of Ripiro Beach and were only associated with two major toheroa beds. Observations found that bivalves are a significant food resource for oystercatchers and the birds have a high predation success rate. There was a significant difference in the density and size structure between toheroa populations in beds that were oystercatcher predation sites and those at no-predation sites. However, even in the areas with the most intense oystercatcher predation, toheroa have persisted over time. While there potentially is a small local impact, overall, the South Island pied oystercatcher is not responsible for the continuing decline of the toheroa across the whole of Ripiro Beach and are not causing devastation as claimed. 
The perceived conservation conflict between the two endemic species is likely incorrect. This research demonstrates the importance of acquiring information on interacting species prior to management action to protect one of those species. Information presented in this thesis can be used to support conservation managers in making informed decisions to protect both the toheroa and the South Island pied oystercatcher.

year: 2020