通过表面钨掺杂大幅提升钯纳米立方体的燃料电池催化性能（英文）

发展兼具高活性和高稳定性的规整非铂电化学催化剂无论对于燃料电池的推广应用还是基础研究都具有重要意义.我们将钯纳米立方体(Pd nanocubes)作为晶种,使用表面掺杂的手段制备了一种表面结构规整的钨掺杂钯纳米立方体(W-doped Pd nanocubes).通过改变合成过程中所加入羰基钨前驱体的量以调控表面钨的原子比例,继而获得了钨原子比例分别为0%,0.8%,1.2%,1.5%的纳米立方体.所制W-doped Pd nanocubes/C催化剂在碱性条件下的氧还原反应中表现出优异性能,其中1.2%W-doped Pd nanocubes/C催化剂性能最佳,在0.9 VRHE时比活性达1.18 mA cm~(-2),质量活性达0.25 A mg~(-1)Pd,分别是商业Pt/C催化剂的4.7倍和2.5倍.研究表明,随着钨的掺杂量从0%增至1.5%,钨掺杂钯纳米立方体的d带中心从-2.49 eV逐渐降至-3.08 eV.同时,光电子能谱结果表明,随着钨掺杂量的增加,钯的3d峰位向低能逐渐偏移,说明了钨掺杂导致了电荷由钨转向钯.而d带中心的下移能够将更多的反键态拉下费米能级,继而导致反应中间体的吸附减弱.因此,由钨到钯的电荷转移导致的d带中心的下移,继而引起的反应中间体对催化剂的吸附作用变弱是氧还原催化活性增强的原因.而过高的W掺杂(1.5%)导致活性的降低也可以用Sabatier规则解释.在循环测试10000圈之后,1.2%W-doped Pd nanocubes/C催化剂的质量活性仅仅减少了14.8%,而商业Pt/C催化剂减少了40%,可见其具有极佳的稳定性.而且循环测试之后的透射电镜表征显示,相比于团聚严重的商业Pt/C催化剂,1.2%W-doped Pd nanocubes/C催化剂仍然分散良好,其形貌也几乎没有发生变化.此外,该催化剂对乙醇氧化反应也表现出优异的性能.在1.0 mol L~(-1)氢氧化钾和1.0 mol L~(-1)乙醇混合溶液中,测试峰电流达6.6 A mg~(-1)Pd,是Pd nanocubes/C催化剂的2.2倍,商业Pd/C催化剂的5.1倍.这同样得益于适量钨掺杂所导致的催化剂d带中心—下移引起的含碳中间体吸附的削弱.经过1000 s的稳定性测试,1.2%W-doped Pd nanocubes/C同样表现出高于商业Pd/C催化剂的稳定性.优异的氧还原和乙醇氧化性能表明所制1.2%W-doped Pd nanocubes/C是一种极具潜力的双功能燃料电池催化剂.

Boosting fuel cell catalysis by surface doping of W on Pd nanocubes

The development of active and durable non-Pt electrocatalysts with well-defined microstructure is of great importance to both fuel cell applications and fundamental understanding. Herein, we report a surface-doping process to prepare well-defined W-doped Pd nanocubes with a tunable atomic percent of W from 0 to 1.5% by using the Pd nanocubes as seeds. The obtained 1.2%W-doped Pd nanocubes/C exhibited greatly enhanced electrocatalytic performance toward oxygen reduction reaction in alkaline media, presenting an enhancement factor of 4.7 in specific activity and 2.5 in mass activity compared to the activity of a commercial Pt/C catalyst. The downshift of the d-band center due to a negative charge transfer from W to Pd intrinsically accounts for such improvement in activity by weakening the adsorption of reaction intermediates. Also, the 1.2%W-doped Pd nanocubes/C showed superior catalytic properties for the ethanol oxidation reaction, showing great potential for serving as a bifunctional electrocatalyst in fuel cells.