其实是一回事啊 就是把文章的创新点写清楚  因为能否发表除了英语和格式达到要求外就是要求创新

why the journal should publish it？

We believe that the findings of this study are relevant to the scope of your journal and will be of interest to its readership.

个人认为第二条其实是让你说下你文章的研究背景和研究意义，在此背景下我们的工作有利于实现什么什么的。。。。。。
关于cover letter 个人认为遵循事实就好，不能一味的谦虚要突出自己文章的创新性和研究价值，不过分夸大就好。望一切顺利！

Submission of a manuscript must be accompanied by a cover letter that addresses the following
questions: What is the novelty of this work? Is the paper appealing to a popular or scientific audience?
Why the authors think the paper is important and why the journal should publish it? Has the article
been checked by a native tongue speaker with expertise in the field? Are you available as a reviewer
for at least three other articles for Applied Energy during the current year? In addition to answering
those five questions, the authors should also describe in one or two paragraphs the significance of
their work and what new information is described in the manuscript，

主要写研究内容怎么跟这个期刊主旨契合的

是所有的杂志都这五个问题，我也刚写了，个人认为还是你解决了什么难题吧，我发给老师看了，她也没说有问题。

还是着重说下文章的亮点和应用