| 摘要: | 由於大氣中二氧化碳濃度逐漸增加而導致全球暖化，在這種情況
下，電化學二氧化碳還原反應(carbon dioxide reduction reaction, CO2RR)
則是減少二氧化碳排放最有效的方法之一。應用於CO2RR 之觸媒必
須滿足優秀的電化學性能、低成本以及良好的穩定性等要求。因此在
本研究中，製備了碳支撐氧化鋅與銀((ZnO)xAg)觸媒並將其作為
CO2RR 觸媒。在銀中添加氧化鋅不僅可以減少貴重金屬的使用，也可
以藉由修飾其電子結構來提高一氧化碳法拉第效率和選擇性。
本研究分為三個部分。在第一部分，製備了ZnO/Ag 原子比為3/1
和2/1 的(ZnO)xAg 觸媒。(ZnO)3Ag 具有與Ag 相同的一氧化碳法拉第
效率，但由於適量的氧化鋅添加造成表面和電子的修飾，其質量活性
高於Ag。
在第二部分中，氫氣熱處理被用以改善觸媒的CO2RR 性能。根據
X 光電子能譜儀和X 光吸收光譜儀的結果，氫氣熱處理可以部份還原
氧化物並調整化學狀態，所以能提高電化學效率。在-1.1 V 下，
(ZnO)3Ag-H 展現較好的一氧化碳法拉第效率(84.6 %)，在7 小時的穩
定性測試中效率衰退9.2 %，優於(ZnO)2Ag-H 的一氧化碳法拉第效率
(77.3 %, 衰減15.2 % /7 小時)。
第三部分研究了電解質對(ZnO)3Ag-H 的CO2RR 性能影響。在0.5
M 氯化鉀中，(ZnO)3Ag-H 表現出好的一氧化碳法拉第效率和穩定性
(89.0 %和衰退12.9 % /22 小時)相較於在0.1 M 碳酸氫鉀中(84.6 %和
衰退14.3 % /8 小時)和 0.1 M 氯化鉀中的表現(89.7 %和衰退14.0 %
/8 小時)，因為氯離子可以修飾銀的表面以形成更多的活性位點，並且
抑制CO2RR 的競爭反應-析氫。在濃度效應下，較多的氯離子會更有
效阻擋活性位點上的析氫反應，減緩其反應速率，而得到較佳的穩定
度。綜合以上的結果，本研究強調，透過適當的電解液調控和氫氣熱
處理，在銀觸媒中添加氧化鋅可以降低貴重金屬的成本，並在CO2RR
反應中提高一氧化碳法拉第效率和穩定性。;The gradual increase in the concentration of carbon dioxide (CO2) in
the atmosphere leads to global warming. In this event, electrochemical
carbon dioxide reduction reaction (CO2RR) is one of most effective
strategies to eliminate CO2 emissions. The catalysts applied for CO2RR
must meet the requirements such as excellence electrochemical
performance, low cost, and good stability. In this study, the carbonsupported
(ZnO)xAg catalysts are prepared and applied as CO2RR catalysts.
The addition of ZnO into Ag not only reduces the use of noble metals, but
it also modifies the electronic structure to enhance CO faraday efficiency
(FE) and selectivity.
This research is divided into three parts. In the first part, the binary
(ZnO)xAg catalysts with ZnO/Ag atomic ratios of 3/1 and 2/1 have been
prepared. (ZnO)3Ag shows the same CO FE as Ag, but its mass activity
(MA) is higher than that of Ag owing to the proper amount of ZnO addition,
which induces surface and electronic modification.
In the second part, H2 heat treatment is applied to promote the CO2RR
performance of the catalysts. According to X-ray photoelectron
spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) results, the
H2 heat treatment is able to partially reduce oxides and tune the chemical
state so that the electrochemical efficiency can be enhanced. (ZnO)3Ag-H
displays the best performance where the CO FE is 84.6 % and decays 9.2 %
/7 hrs at -1.1 V (vs. RHE), superior to (ZnO)2Ag-H with CO FE of 77.3 %
and 15.2 % decay/ 7 hrs.
In the third part, the electrolyte effect on the CO2RR performance of
(ZnO)3Ag-H is studied. In 0.5 M KCl, (ZnO)3Ag-H shows a better CO FE
and stability (89.0 % and 12.9 % decay/ 22 hrs) than those in 0.1 M KHCO3
(84.6 % and 14.3 % decay/ 8 hrs) and 0.1 M KCl (89.7 % and 14.0 % decay/
8hrs) because Cl- can modify Ag surface to form more active sites and
suppress the competitive hydrogen evolution reaction. In terms of the
concentration effect, more Cl- anions can block some active sites to slow
down the hydrogen evolution reaction more, and results in a better stability.
Based on the above results, this research highlights that with proper
electrolyte and H2 heat treatment, the addition of ZnOx into Ag catalysts can
decrease the cost of catalysts and enhance CO FE and stability during
CO2RR. |
