高效可见光非金属碳化硼光阴极的微、宏观形貌控制合成及光电化学水分解研究

Exploring efficient, stable and low-cost photoelectrode materials is one of the hot issues in the field of photoelectrochemical (PEC) water splitting. Metal-free photocatalysts were discovered as a new group of photocatalysts and photoelectrode materials recently. We reported a novel metal-free photocatalyst ‘boron carbides B4C’ which could be adopted as photocathode materials for PEC water reduction. It has received considerable attention due to its visible-light activity and PEC stability. However, the commercial B4C used in previous report suffers from irregular morphology, low PEC activity and extremely high temperature of crystallization. In addition, the mechanism of PEC water reduction for the new photocathode materials B4C is still unknown. To solve the above-mentioned problems, the present project proposes to fabricate B4C/C photocathodes with controllable macro-morphologies by in-situ growing B4C on different free-standing carbon electrodes. The free-standing C electrodes also serve as C sources for the in-situ growing of B4C. By investigating the mechanism of in-situ growing B4C on different C electrodes, the micro-morphologies of B4C/C photocathodes can be controlled. The inherent relations between the micro-/macro-morphologies of B4C/C photocathodes and their PEC performances can be established. The influence of PEC reaction conditions on the PEC performances of B4C/C photocathodes will also be studied. Therefore, the mechanism of PEC water reduction for the new B4C photocathode materials can be disclosed. The fabricated B4C/C photocathodes will also bestow a new property of PEC water reduction on the traditional functional carbon materials, which means the B4C/C will possess multi-functional properties. Conclusively, by conducting the present proposal, we will obtain valuable experimental references for the synthetic methodologies of B4C, the characteristics and mechanism of PEC water reduction for B4C, and the exploration of new multi-functional carbon materials.

高效、稳定、廉价的光电极材料是光电化学（PEC）水分解的研究热点。非金属光催化剂是近年发现的一类新型光催化剂和光电极材料。项目申请人报道了新型非金属光催化剂碳化硼（B4C）的PEC光阴极水还原性能，因其可见光活性、PEC性质稳定而受到广泛关注。然而商用B4C结晶温度高、无规则形貌、活性低，且其PEC水分解机理尚不明了。针对上述问题，本研究提出以不同形貌的可伫立碳电极为碳源原位生长B4C，制备宏观形貌可控的B4C/C光阴极。研究B4C的原位生长机理，并对其微观形貌进行控制。建立B4C/C的微、宏观形貌以及PEC反应条件与其PEC性能之间的内在关系，揭示其PEC水还原机理。B4C/C还将赋予传统碳基功能材料PEC水分解性能，形成新型复合功能碳基材料。本项目的开展将为B4C的合成方法学、B4C的PEC水还原性能和机理以及新型碳基复合功能材料的开发提供丰富的实验和理论依据。

非金属光催化剂是近年发现的一类新型光催化剂和光电极材料。碳化硼（B4C）是一种典型的富硼类非金属光催化剂，由于合成这种材料所需要的条件比较苛刻，比如结晶温度较高，使其难以进一步被广泛使用。本项目的研究分两个部分展开。首先，考察了系列过渡金属（铁、钴、镍、铜、锌）催化剂来降低碳化硼结晶温度。发现采用镍的效果最好，能够在850℃下合成出介孔碳化硼，且比表面积高达130.55 m2 g-1，是商业碳化硼的27倍。通过光催化还原CO2和羟基自由基测试，进一步考察了采用镍作为催化剂在不同温度下制备的碳化硼光催化性能，发现950°C下合成的碳化硼具有最高的光催化活性。结果表明碳化硼的结晶度和比表面积都会影响其光催化性能。本研究为晶体B4C的低温合成提供了重要参考。在第一部分研究结果的基础上，本项目采用柔性碳纤维布（carbon cloth, 简写作CC）为基底，首先用电镀法在碳布表面沉积镍颗粒作为降低B4C结晶温度的催化剂。其次，采用化学气相沉积法（CVD），利用碳布为碳源，在碳布表面原位生长制得B4C负载的碳布柔性光阴极（CC/B4C），该制备方法有效保持了碳纤维布的柔韧性。最后，在制得的CC/B4C表面掺杂少量的Mo，作为光电化学分解水的助催化剂，制得CC/B4C-Mo复合柔性光阴极。光电化学测试结果表明，在-0.8V（相对于甘汞电极），一个模拟太阳光条件下，柔性CC/B4C-Mo光阴极的光电流密度为155 μA cm-2，分别比CC/B4C和对比样CC/B4C/Au高出55.0%和19.2%。因此，Mo比贵金属Au能更有效的提高碳化硼的光电化学性能。综上所述，本项目圆满完成了既定目标，为B4C的合成方法学、B4C的PEC水还原性能和机理以及制备新型碳基复合功能材料提供了丰富的实验和理论依据。